So, what is it that makes an engine accelerate?

[steelcomp]

I've been waiting a LONG time for the opportunity to present itself to open this can of worms. This is the grand daddy of all questions regarding engine performance, and I'm really curious as to who thinks what. What is it about an engine that makes it accelerate? Why does one engine accelerate better, or faster than another comparable engine from point A to point B? Lets face it...this is what wins races, not dyno numbers. So, is it horsepower? Torque? Both? Neither? :idea:
Let 'er rip. :D

[Morg]

To quote a wise man "Money$$$$$$$$$$$$$$$$$$$$$$$"
I'm sure this thread will take a few turns

[MikeF]

Usually.............this.
http://i22.ebayimg.com/01/i/05/c7/66/39_1.JPG
:p

[Infomaniac]

have you ever searched Torque vs HP on this site?
LOL
So the engine accelerating or the vehicle?

[bottom feeder]

Here is my engine accelerater
http://www.***boat.com/image_center/data/520/1501LOUD_BUTTON-med.JPG
Sorry its not a more complex answer

[Oldsquirt]

I see the answer being contained in Sir Isaac Newton's First Law of Motion: An object at rest tends to remain at rest, and an object in uniform motion tends to remain in uniform motion, absent the application of an unbalanced force.

[steelcomp]

have you ever searched Torque vs HP on this site?
LOL
So the engine accelerating or the vehicle?
What's the difference? A load is a load. What makes one engine accelerate a given "load" from point A to point B faster than another? If the rpm range you anticipate operating in is, for instance, from 3000 to 6000rpm, won't the combination that will pull the "known load" from the bottom to the top the quickest ALWAYS be the engine to run regardless of HP? So what makes the difference?

[steelcomp]

I see the answer being contained in Sir Isaac Newton's First Law of Motion: An object at rest tends to remain at rest, and an object in uniform motion tends to remain in uniform motion, absent the application of an unbalanced force.
Think acceleration rate...

[MikeF]

So what makes the difference?
Traction!

[BUSBY]

ok ... wait a minute ... I have to warm up my fingers ...

[Carnivalride]

Now you've gone and done it, there's a lot of variables here!
Bore, stroke, rotating mass, port velocities, compression, flame fronts, lobe designs, scavenging, on and on. :hammerhea :hammerhea :hammerhea
This is awful technical for me this time at night I'll have to think about this and revisit when I'm more awake. :eek: :messedup: :idea: :idea:

[BUSBY]

Well I started thinking about this the other day when posting on the other thread ... and I suppose I'll start with a brief brief on the relationship between a connecting rod and it's crankshaft because I think it's important to engine acceleration.
It seems simple at first to think that when the crankshaft is at 0 (top dead center) ... with the piston is all the way up ... and when the crankshaft is at 180 (bottom dead center) the piston is all the way down. That part's easy.
What happens when the crankshaft is at 90? You'd think that the piston is halfway down the bore, right? Well that's not exactly true. The angularity of the rod at that point brings the piston down a little bit further - the connecting rod length is the hypotenuse of a triangle where the short side is the sideways distance from the center of the cylinder to the center of the crankpin.
What does this mean to an engine tuner? Well ... there are several issues to discuss: ignition timing, combustion chamber growth rate, vacuum production, camshaft events, etc.
The first thing I'd like to address is the chamber growth rate. Because a piston in a 1.5:1 rod ratio motor moves down from TDC a little bit quicker in a given amount of crank rotation, a short rod combo will increase the chamber size quicker, creating more vacuum, bringing greater pull through the intake port, setting up a high velocity charge for later on in the stroke. Because a short rod combo pulls harder through the ports, it will develop torque at a lower RPM than a long rod motor ... all else being kept equal. At higher RPM, it will run out of breath sooner since it is pulling harder through the ports ... so a long rod combo should make more horsepower by making more torque higher up in the RPM range.
God I love this stuff ...
Another issue is that because the 1.5:1 motor's piston moves faster near TDC than does a 2:1 motor ... the intake valve opening should be given consideration. Because the 1.5 motor develops stronger vacuum ... the intake valve could be opened later to take advantage of the greater pull. Or, because the exhaust gasses are being forced out a little harder (piston approaching top of stroke quicker) one of two things could happen: Either there will be a higher residual pressure in the combustion chamber because there is a bottleneck downstream in the exhaust and the intake should be opened later to allow the pressure to equalize; or there will be a greater scavenging effect from the higher velocity exhaust gas in a header primary, allowing the intake to be opened earlier.
Generally ... I believe and could be wrong ... the short rod motor can deal with greater valve overlap than a long rod motor.
Because the long rod motor's piston moves away from BDC faster than does the short rod motor's piston, the intake valve MUST be closed sooner in a long rod motor ... or else you run the risk of pushing the fresh charge right back out the intake port and losing dynamic compression. The exhaust valve should also be opened later.
Chamber growth rate is something that should be very interesting to people looking at their ignition: the 1.5:1 motor's combustion chamber grows quicker leaving TDC than does a 2.0:1 motor, which allows more room for the expanding combustion gasses, which lowers the early cylinder pressure slightly. This means a short rod motor needs slightly more ignition timing to develop peak cylinder pressure earlier than in a long rod motor. Furthermore, because the piston is moving fastest when the rod and crank are at 90* from one another, and because that happens sooner with a short rod motor, higher cylinder pressure at that point will create the greatest leverage on the crankshaft.
A friend of mine Matt and I talk for days about this ... and it is the basis of the engine and it's acceleration IMO ... one thing to remember is that an engine is an air pump it sucks it in and spits it out ... it's all about how easy you make it happen.
My fingers are now tired.

[steelcomp]

- the connecting rod length is the hypotenuse of a triangle where the short side is the sideways distance from the center of the cylinder to the center of the crankpin. Not always, and in fact, only part of the time. The amount of time this is true is directly related to the rod/str. ratio.

[BUSBY]

oh so picky ... I told you ... my fingers are tired ...

[BUSBY]

Not always, and in fact, only part of the time. The amount of time this is true is directly related to the rod/str. ratio.
Wait a minute ... the amount of time (while related to the rod/str ratio) is meaningless ... the amount of time is a determined only by RPM ... how little of the time it is there has nothing to do with the degree/angle ...

[MikeF]

Not always, and in fact, only part of the time. The amount of time this is true is directly related to the rod/str. ratio.
When the rod and crank throw are at a true 90deg. :rollside:

[steelcomp]

Wait a minute ... the amount of time (while related to the rod/str ratio) is meaningless ... the amount of time is a determined only by RPM ... how little of the time it is there has nothing to do with the degree/angle ...OK...sorry...I meant time in crank degrees of rotation. But you're right...I'm just bein picky. It's really irrelevant weather it's the long leg or short leg.
BTW...you're all f'd up with this short rod fantasy you have. :argue:

[steelcomp]

When the rod and crank throw are at a true 90deg. :rollside:Impossible for the rod to be the hypo. if the rod and throw are @ 90*.

[BUSBY]

BTW...you're all f'd up with this short rod fantasy you have. :argue:
Hey now ... I don't have any fantasy about your short rod! We're talkin' engines here ... not what your deficiencies are.
If you want a more rapid RPM ramp, you'll need a short stroke/short rod/big bore motor, period. It's been proven. You'll never change the facts ... including how short you might be.

[boatslayer]

:confused:

[Oldsquirt]

Think acceleration rate...
Since acceleration itself is a rate , specifically the rate at which velocity changes versus time, I assume by this you are referring to the rate at which acceleration changes versus time.
Well I started thinking about this the other day when posting on the other thread ... ..........
.......................
......My fingers are now tired.
For years I've had a lot of similar stuff rattling around in my poor brain. I've always assumed that the engineers somewhere must have written the necessary formulas to relate the expansion rate of the burning gas to piston position and speed, to cylinder pressure, to crank angle, etc, etc. Got to be a big Kray somewhere capable of running simulations, right? :D

[Oldsquirt]

Impossible for the rod to be the hypo. if the rod and throw are @ 90*.
Correct. At this point the hypotenuse would be the line from crank centerline to piston pin centerline.

[Norseman]

I've been waiting a LONG time for the opportunity to present itself to open this can of worms. This is the grand daddy of all questions regarding engine performance, and I'm really curious as to who thinks what. What is it about an engine that makes it accelerate? Why does one engine accelerate better, or faster than another comparable engine from point A to point B? Lets face it...this is what wins races, not dyno numbers. So, is it horsepower? Torque? Both? Neither? :idea:
Let 'er rip. :D
Steel;
Engine don't accelerate, vehicles do. But some do increase RPM faster than others..... :) :)

[steelcomp]

Since acceleration itself is a rate , specifically the rate at which velocity changes versus time, I assume by this you are referring to the rate at which acceleration changes versus time.
For years I've had a lot of similar stuff rattling around in my poor brain. I've always assumed that the engineers somewhere must have written the necessary formulas to relate the expansion rate of the burning gas to piston position and speed, to cylinder pressure, to crank angle, etc, etc. Got to be a big Kray somewhere capable of running simulations, right? :D
Old...yes, this is all about acceleration over time, since we're trying to get from point A to point B in the least amount of time as possible. Increasing velocity is increasing acceleration, etc, but that's symantics AFA my question.
What makes an engine accelerate? Your second paragraph touches on where I think this will eventually go.
Busby, in his not-so-eloquent terms says it's the short rod that helps. (I'll get back to you and your short jokes later, pal.) There's too many other things to consider to say that the rod ratio by itself is going to "make" an engine accelerate or not. But where's the motivation coming from? I'm thinking more in terms with what's going on in the combustion chamber. Good burn vs. better burn, vs. best burn. In this sense, Daryl Morgan may have a point.

[steelcomp]

Hey now ... I don't have any fantasy about your short rod! We're talkin' engines here ... not what your deficiencies are.
If you want a more rapid RPM ramp, you'll need a short stroke/short rod/big bore motor, period. It's been proven. You'll never change the facts ... including how short you might be.
I'll say this.
OK...No I won't.
However, in regards to your "short" comment, think about it this way, BIG guy. Put you in your boat, run it. Now put ME in your boat.
Advantage who? :yuk: :D

[cstraub]

For an engine to accerate: Correct sequence of events....

[BUSBY]

Busby, in his not-so-eloquent terms says it's the short rod that helps. (I'll get back to you and your short jokes later, pal.) There's too many other things to consider to say that the rod ratio by itself is going to "make" an engine accelerate or not. But where's the motivation coming from? I'm thinking more in terms with what's going on in the combustion chamber. Good burn vs. better burn, vs. best burn.
Well ... I agree 100% ... but when we're speaking about an internal combustion engine, we're speaking about volumetric effiency, right? And how does the stuff get into the chamber in the first place? By the pistons downward motion creating a vacuum. If the rate of the downward motion directly effects the VE, then the rod ratio it very important in equating what your goals are when building an engine. In a not so eloquent term ... I will explain to you Scott that this is the first stroke ... the intake stroke ... the beginning of how we make an engine run.
Once you grasp this idea ... we'll work on the next stroke ... compressing what we've filled the cylinder with ... it's called the "compression stroke", let me know when you're ready Scott ... in your post you were moving onto things way too quick, kinda prematurely, but you might be used to that ...

[BUSBY]

For an engine to accerate: Correct sequence of events....
hey ... I didn't get to page two yet ... I see you have already started speaking about what I am getting to ...

[cstraub]

When a swimmer finds his stroke and kick rythum he or she is fast.....
When a cyclist finds his pedeling rythum he or she is fast. . .
When a runner finds his stride he or she is fast. . .
When an engine has a tuned induction and exhaust path, it is fast. . .

[BUSBY]

When a swimmer finds his stroke and kick rythum he or she is fast.....
When a cyclist finds his pedeling rythum he or she is fast. . .
When a runner finds his stride he or she is fast. . .
When an engine has a tuned induction and exhaust path, it is fast. . .
well put ... timing is everything ...

[MikeF]

Impossible for the rod to be the hypo. if the rod and throw are @ 90*.
What I was getting at was,
The piston would be moving at it's fastest speed at this point at a given rpm. :boxed: And by that time the BANG has already done most of it's work.

[BUSBY]

I hate to have to quote myself ...
What happens when the crankshaft is at 90? You'd think that the piston is halfway down the bore, right? Well that's not exactly true. The angularity of the rod at that point brings the piston down a little bit further - the connecting rod length is the hypotenuse of a triangle where the short side is the sideways distance from the center of the cylinder to the center of the crankpin.
Pythagoras was a Greek mathematician who lived about 2500 years ago, and who developed the most famous formula in geometry, possibly in all of mathematics! He proved that, for a right triangle, the sum of the squares of the two sides that join at a right angle equals the square of the third side. The third side--the side opposite the right angle--is called the hypotenuse of the right triangle. The two shorter sides are usually called "legs."
This formula is called the Pythagorean Theorem in honor of Pythagoras. It is usually written as the equation below, where a and b are the measures of the legs of the triangle and c is the measure of the hypotenuse.
http://www.***boat.com/image_center/data/520/2358formula.gif
So with my original post of the crank being at 90* (from TDC) ... the hypotenuse would have to be the rod angle :squiggle:
http://www.***boat.com/image_center/data/520/2358hypotenuse.gif

[Oldsquirt]

So with my original post of the crank being at 90* (from TDC) ... the hypotenuse would have to be the rod angle :squiggle:
http://www.***boat.com/image_center/data/520/2358hypotenuse.gif
Ummm, don't you mean rod length? :)

[MikeF]

Picture this,
http://www.***boat.com/image_center/data/500/1532358hypotenuse1.gif
Large black circle is crank journal.
Red circle is rod journal.
Yellow circle is piston pin.
Piston speed should be at it's max in this position. Yes/no. Or is it at 90deg to the bore? :boxed:

[Norseman]

Picture this,
http://www.***boat.com/image_center/data/500/1532358hypotenuse1.gif
Large black circle is crank journal.
Red circle is rod journal.
Yellow circle is piston pin.
Piston speed should be at it's max in this position. Yes/no. Or is it at 90deg to the bore? :boxed:
Mike;
Piston speed is Zero at TDC
Maxium piston speed should be at two points relative to crankshaft rotation about 75 degrees and about 285 degrees of crankshaft rotation
Maximum piston acceleration will be about 10 degrees before and after top dead center.
Bob

[MikeF]

Mike;
Piston speed is Zero at TDC
Of course. :rollside:

[Beer-30]

I've been waiting a LONG time for the opportunity to present itself to open this can of worms. This is the grand daddy of all questions regarding engine performance, and I'm really curious as to who thinks what. What is it about an engine that makes it accelerate? Why does one engine accelerate better, or faster than another comparable engine from point A to point B? Lets face it...this is what wins races, not dyno numbers. So, is it horsepower? Torque? Both? Neither? :idea:
Let 'er rip. :D
Throttle position!!
LOL. :D

[BUSBY]

Ummm, don't you mean rod length? :)
No ... I meant angle, refering to the diagram the length of the rod was irrelevant ... just trying to make sure that we were all speaking of the same angle/segment of the triangle ...

[BUSBY]

What happened to Scott? I'm ready to talk about the next stroke! Compressing what we brought in ... and what effects heat plays ...

[Oldsquirt]

No ... I meant angle, refering to the diagram the length of the rod was irrelevant ... just trying to make sure that we were all speaking of the same angle/segment of the triangle ...
Yeah, I know what you were getting at, just busting your butt about calling a straight line(the hyp) an angle. :)
BTW, as interesting as I find this, it's giving me flashbacks to my physics, geometry, trigonometry and, worst of all, calculus courses taken 30-something years ago. :D

[BUSBY]

Yeah, I know what you were getting at, just busting your butt about calling a straight line(the hyp) an angle. :)
BTW, as interesting as I find this, it's giving me flashbacks to my physics, geometry, trigonometry and, worst of all, calculus courses taken 30-something years ago. :D
tell me about it ... my brain hurts ... and to think when falling asleep in High School because it was so boring, I didn't know I would have to relearn it in college and then actually want to use it later in life ... :messedup:

[Norseman]

tell me about it ... my brain hurts ... and to think when falling asleep in High School because it was so boring, I didn't know I would have to relearn it in college and then actually want to use it later in life ... :messedup:
What's scary is that we actually want to use it!!!!!
I never believed the teachers that said that one day this stuff would be useful. But I knew everything when I was in high school.
My kids don't believe me that they will need it later either!!! :rolleyes: :rolleyes:
Of course now they can use programable calculators and computers to work the numbers. We weren't so lucky back in the day!!!

[BUSBY]

My kids don't believe me that they will need it later either!!! :rolleyes: :rolleyes:
Tell me about it ... they think I'm the uncool one! :rolleyes:
My son is 11 now ... wait 5 more years ... he'll be all up in my garage ... and I'll have to kick his ass!

[steve d]

Are you only talking about reciprocating and valve geometry or will you let the fuel to air ratio factor in?....Steve

[LakesOnly]

What is it about an engine that makes it accelerate? Why does one engine accelerate better, or faster than another comparable engine from point A to point B? Is it horsepower? Torque? Both? Neither? :idea:Neither. For me, it's usually that large breasted woman onshore and looking at my boat that gets my motor runnin' hard... http://southwindjetboats.com/forum/upload/html/emoticons/boobies.gif
LO
p.s. Sorry 'Comp... :D ...Friday night, ya know... :D

[Norseman]

Tell me about it ... they think I'm the uncool one! :rolleyes:
My son is 11 now ... wait 5 more years ... he'll be all up in my garage ... and I'll have to kick his ass!
I've been trying to get my 11 year old into the garage to work on a couple of projects. So far no good. I'm sure he'll get into it shortly.
His sister is 15 and just wants to see a finished convert in the driveway with her name on it... :cry: :cry:

[Bobbo541]

Dam i got a headache just reading this.

[steelcomp]

I'm Baa-aack! Wow. you guys been busy...talkin a lot of jibberish. :rolleyes:
Brian, don't lecture me, junior. All your engineering ain't going to impress me.
Intake
Compression
Power
Exhaust
Two of these are trying to create the third, and one is a result of three.
Does anyone know what was behind Bill Elliot's domination when he ran his million dollar year?
How about Bob Glidden's Boss 429 based, record shattering pro stock days?
The two have a very common denominator.
It's in the power stroke.
Sure, the intake has to be "effecient", and the squeez is important, but the combustion process, and what takes place in that chamber when the mix is fired, is really all that matters. Figure out how to control that, and make it do what you want it to do, and the rest is elementary. Long rod, short rod, it dosen't matter...you can tailor intake and exhaust to acomodate both, but what you can't do, is allow enough time at TDC, on the compression stroke, to do what needs to be done, with a rod ratio in the 1.5-1.6 range, no matter how good it sucks. :D
Brian, you read what I sent you on Pro Stock Motor...did you take a minute to compute the compression on that motor?

[steelcomp]

the connecting rod length is the hypotenuse of a triangle
BTW...this is your quote, saying that the rod length, not angle, was the hypotenuse of the triangle formed by the three points of piston pin c/l, rod journal c/l, and main journal c/l, as in Mike F's diagram. Again, not always true, and the time in degrees of rotation that it is true is directly proportional to the ratio of the rod/stroke. I'm sure there's a formula somewhere that would tell exactly at what degree the crank needs to be at, depending on the stroke, and length of the rod, for it to become the hypo. of the triangle.

[Moneypitt]

Basically what makes an engine rev is AIR......Everything is associated with the amount of air you can pull through an engine. The more AIR you pull, the more it wants, until terminal velocity is attained, end of acceleration........MP

[BUSBY]

Scott ... Scott ... Scott ...
Don't let me have to break out the goods ... I've forgotten more information than you've probably learned ... :D
But I've taken the stance at this point that it's the X-mas season ... and schooling you should wait unit after the New Year ... that or I've had too much to drink and I feel sorry for you.
We'll work on Compression, Power & Exhaust when I return ... but remember ... all that matters is volumetric efficiency!
Have a great holiday! :D

[steelcomp]

Well ... I agree 100% ... but when we're speaking about an internal combustion engine, we're speaking about volumetric effiency, right? And how does the stuff get into the chamber in the first place? By the pistons downward motion creating a vacuum. If the rate of the downward motion directly effects the VE, then the rod ratio it very important in equating what your goals are when building an engine. In a not so eloquent term ... I will explain to you Scott that this is the first stroke ... the intake stroke ... the beginning of how we make an engine run.
Once you grasp this idea ... we'll work on the next stroke ... compressing what we've filled the cylinder with ... it's called the "compression stroke", let me know when you're ready Scott ... in your post you were moving onto things way too quick, kinda prematurely, but you might be used to that ...
Don't worry Brian, I'll bring you down gently. :D Here...let me throw this at you. Rod length combined with crank stroke and rpm dictate piston speed, yes. The rod length relative to stroke also geometrically dictates where in the rotation of the crank you'll see maximum piston velocities, and accelerations....and while on the subject of geometry, the rod angle relative to the cylinder bore axis is a direct function of rod length. The severity of the rod angle becomes worse as the rod gets shorter relative to stroke, (obviously) and therefore attempts to push the piston through the cylinder wall at any angle below 90 degrees either side of TDC. So from this stand point, piston and cylinder wall life are greatly compromised with the short rod. Parasitic friction is also a MAJOR factor due to sideloading. The short rod also causes the piston to "dwell" at TDC and BDC less time, and the positive and negative acceleration rates are higher as well, which cause lots of positive cylinder pressure, especially at overlap which can shove a significant amount of semi-burned gases back up the intake port. As these gases are largely inert, their presence in the "new" inlet mixture is a real negative when looking for an efficient burn. The dwell time the piston spends at or near TDC also dictates the amount of cylinder pressure that's "useful". It also effects the rate of valve opening and closing events. I'll let you digest that for a bit.

[steelcomp]

Scott ... Scott ... Scott ...
Don't let me have to break out the goods ... I've forgotten more information than you've probably learned ... :D
But I've taken the stance at this point that it's the X-mas season ... and schooling you should wait unit after the New Year ... that or I've had too much to drink and I feel sorry for you.
We'll work on Compression, Power & Exhaust when I return ... but remember ... all that matters is volumetric efficiency!
Have a great holiday! :D
Merry Christmas, Brian! :D
And everyone else, too. Have a happy holiday, and be safe! :rollside:

[fc-pilot]

Wow, this has been a fun read. I missed comedy central tonight, but reading you guys going at it took care of my loss.
Paul

[BUSBY]

Scott ... While I understand your fixation on long rods ... you have to admit that the short rod is a much better and more common scenario ... no matter how you look at it ...
Now ... don't look at this in your normal way, we are speaking about engines here! :D

[ECeptor]

Whomever mentioned Newton was on the right track.
It's all about F=ma....force = mass times acceleration.
So, what makes anything (engine or otherwise) accelerate? The relationship between force and mass. Increase your forces (BMEP, torque, etc) and reduce your mass (rotating mass, apparent mass - i.e. inertia, linear mass - weight of your vehicle or your own fat a$$) and you'll accelerate faster.
Everything you do to a vehicle to make it accelerate faster can be classified as either a force increaser or a mass reducer.

[BUSBY]

Well it's 1:40am and I've put all of the x-mas goodies out for the kids ... and I thought of Scott ... (steelcomp) ...
I felt sorry for him and his thoughts ... I figured that I would come out here and say that it's all good ... that it's okay for him to have an obsession with "long rods" ... and that it's okay to imagine that size matters.
Merry X-Mas Scott ... and Happy New Year!
:D

[steelcomp]

Well it's 1:40am and I've put all of the x-mas goodies out for the kids ... and I thought of Scott ... (steelcomp) ...
I felt sorry for him and his thoughts ... I figured that I would come out here and say that it's all good ... that it's okay for him to have an obsession with "long rods" ... and that it's okay to imagine that size matters.
Merry X-Mas Scott ... and Happy New Year!
:D
LOL!! Well, at least someone was thinking of me last night!! I'm touched. :rolleyes:
1:40 in the morning, on X-mas eve???...who's obsessing? :D
Short rods suck! (get it...suck...LOL!!! Jeeezzzz...I'm killin' me, here!)
Brian, yes, it's all good, and I'm enjoying out "debate". I'll look forward to a new year of putting you in your place. :D
Merry Christmas, and a Happy New Year to you and your family, as well.
Peace, brotha.

[Gearhead]

Geometry is just one of the issues in consideration and probably not the most important. Other items such as port velocity, the amount of swirl and/or tumble in the combustion chamber and component weights have a great affect on engine acceleration rate. A good portion of the power/performance increases in Pro Stock over the last few years are from acceleration rate and not neccesarily power. And this again opens a very long and technical issue and then discussion of engine cycle analysis may begin which deals with the cyle of each individual cylinder.
I am attaching below a post from Darin Morgan, the R&D guy at Reher and Morrison in reply to rod lengths and ratios. He is one sharp cookie. This post was copied from speedtalk.com engine forum.
Darin Morgan
Show Guest
Joined: 02 Nov 2004
Posts: 214
Location: Arlington Texas
Posted: Fri Dec 02, 2005 9:29 am Post subject: port size vs rod ratio?
--------------------------------------------------------------------------------
Just about everyone I know is brought up to believe this. The GM engineers believed it to until we proved it to be false. In 1995 Reher Morrison conducted an R&D project funded by General Motors to once and for all prove the Rod ratio theories that everyone subscribes to. In a tall deck small block Chevy the rod ratio was changed from 5.550 to 6.650. The difference in ratio was 1.59 to 1.91. The difference in power? NOTHING, not one single horse power difference. The dyno sheets looked identical in every way all the way up to 9000rpm. That is why I now say its a fallacy.
The above post are my words but the rest of the text posted was by another member on this board. I was responding to his post. Just wanted to clarify that.
Now, I once again want to clarify my point on Rod Ratio so nothing I said is taken out of context. The test we did was from 1.59 to 1.9:1. I never stated that above or below those points that there may or may not be daemons lurking. From what I have seen with the older 265 engines with ratios in the 2.15:1 range and the extreme 500+cubic inch small blocks in the 1.3:1 range I can safely say that there are problems with induction system lag above 1.9:1 and frictional power losses, parts damage and decreased component life below 1.5:1. Evaluating the differences in power output from 1.3:1 to 2.15:1 would be impossible because of all the other variables that must be changed in order to achieve that task. I think its a mute point any way because in each case they used what they had to as far as block and deck height as is the case today. We now have the Aurora block with 8.200 decks so we don't have to put up with 2.15:1 rod ratios. What I am trying to get across, is that trying to build an engine around an "ideal rod ratio" is a losing proposition. Design the piston with the ring package properly compacted and spaced , put the pin as high as possible so as to not intrude on the oil ring groove, and connect it to the crank what ever stroke that may be. The rod is dictated by the piston design, stroke and deck height not a preconceived "ideal " rod ratio.
Before you blast me with obscure engine combinations I must say, NO I am not condoning sticking a 4.750 stroke in a 9.8 deck block with a 1.2 compression height piston. A little mechanical common sense has to come into play here as well.
_________________
Darin Morgan
R&D-Cylinder Head Dept.
Reher-Morrison Racing Engines
1120 Enterprise Place
Arlington Texas 76001
817-467-7171
FAX-468-3147

[steelcomp]

We've already visited Daryl's 9000 rpm test motor and it's results on another thred, and again, I call BS on those results. He's also not the only one out there who know's what he's doing, and by what I've learned from others more knowledgable, IMO, there is a significant emphasis on an optimum rod ratio when designing a motor. This therad is getting too focused on rod ratio, though, and not enough on other areas of engine dynamics that more contribute to the engine's ability to accelerate. I was trying to get away from the rod ratio debate, as that's been going on, and will continue to go on for decades. Here's a link if you want to check it out.
http://www.***boat.net/forums/showthread.php?t=99508&page=3&pp=25
Now lets move on from the rod ratio issue. Although important, it's relatively far down on the list of "what makes useful power".

[Gearhead]

Thanks Steelcomp. I'll take a look at the thread later this evening.
I too don't fully agree with what Darin had to say and have some basic rod ratios we try to achieve in our hi rpm competition eliminator engines.
Has there been any threads on Hot Boat forum dealing with port velocities and/or the effects of swirl in the combustion chamber and acceleration on a max performance high rpm (max efficiency) engine? Or the affects on acceleration using lighter weight components in the bottom end?
Thanks!
Gearhead

[steelcomp]

Thanks Steelcomp. I'll take a look at the thread later this evening.
I too don't fully agree with what Darin had to say and have some basic rod ratios we try to achieve in our hi rpm competition eliminator engines.
Has there been any threads on Hot Boat forum dealing with port velocities and/or the effects of swirl in the combustion chamber and acceleration on a max performance high rpm (max efficiency) engine? Or the affects on acceleration using lighter weight components in the bottom end?
Thanks!
Gearhead
Nope. Haven't heard anyone talk about dome shaping to accelerate swirl, detonation reduction through better piston/chamber relationship, or boundry layer analysys, either.
Those types of topics are what I was hoping to get into with this discussion.
Thanks for joining in! :D

[Gearhead]

Steelcomp, I just had the chance to go back and scan the thread that included the rod ratio comment copy of DM and apologize for posting some of the same old stuff again. One of the post in the thread from cstraub69 when he was at PRI visiting with a drag race engine builder that was considering building road race engines reminded me of a story from a camshaft development session we attended in Detroit about ten years ago. Prior to looking at the actual cam designs, the sessions spent quite a lot of time in the design and matching all the other related components for the intended rpm use. We studied the wire size, number of coils, materials, etc and the mathematical harmonics of the spring and at what RPM this takes place. Presently a SpinTron is utilized to study these relationships in running engines.
Anyway, after the long study of spring, camshaft rates and rpm relationship where the design desire was maximum power while controlling the valve train for longevity, the question was asked by the instructor, "Do we have any drag race engine developers in the group", to which three of us acknowledged. He then stated, "Well, you guys can throw a lot of our study out the window! We have been studying controlled valve trains and inductions and you guys deal in what we refer to as "CONTROLLED DESTRUCTION!"…".
Now I need to apologize for what I have provoked. I asked you in a previous post if there were any threads along some of the relative lines of engine development with port velocities and/or the effects of swirl in the combustion chamber and acceleration on a max performance high rpm (max efficiency) engine? Or the affects on acceleration using lighter weight components in the bottom end?
I apologize because this can become a very long post, even for general discussion purposes. I think I'll break this up into three related post so that it will be easier to respond. I am going to try and keep these post in as general terms as I can and not get into difficult to understand. These thoughts are not absolutes… just some info to promote discussion. I am not the expert.

[Gearhead]

Mechanical design of bottom end in reference to rod ratios: In maximum performance engines we need to keep the entire engine parameters in mind as the engine is a big air pump and we are trying to control this pump in a particular RPM range. From a mechanical point of view the ratio will affect many areas such as load on the cylinder wall, etc. From an engine rotation point of view the rod ratio will affect where the piston is in relation to valve events in the rotation or timing of events. For me this needs to balance with the cylinder head and port flow characteristics. In elementary terms a limited port for a particular size engine and rpm range may be assisted by a long rod or a short rod may help improve the initial signal or response from and extremely large port during the intake cycle. The longer rod provides a longer burn cycle during the power stroke. A very general statement is in a given engine a long rod may work better in a hi rpm application and a short one may help in a lower rpm application. In basic theory I tend to lean towards Smokey Yunich's theory of putting the longest rod in the engine, but there are exceptions. From a mechanical point of view, I also feel stroke length has a correlation with desired rpm range. Use a shorter stroke for hi rpm and a longer stroke for lower rpm torque and power. I'll step out on a short limb here and say for the RPM range used in a jet boat, I prefer a stroke in the range of 4" to about 4 3/8" for the best native mechanical advantage. In a BBC with a fairly normal induction a shorter stroke will have a higher RPM power curve and a longer stroke will have a lower RPM power curve. Now with the advent of impellers in the AA to AAA range, longer strokes can be used. Bottom line. The power curve of the engine needs to match the actual use be it impeller sizing, gearing, prop, etc.
Back to mechanical bottom end…. Generally, depending on the particular engine and use, I like to see a rod ratio in the 1.5 to 1.9 range. Sometimes the combination forces us to go a little lower. Now, in these maximum effort mountain motors that Kaase and other build that exceed 700 cid, they pretty well have to use these tall block and rods. My gosh… have you looked at the bottom end with a 5" to 6" crank installed? Man, that is a lot of metal moving around in there and just imagine the side load on the cylinder walls that from a time frame is exerted over a long time. (Low RPM, High torque = high pressure for a long period of time) So, yes… for any life we pretty well have to use the tall blocks and long rods and we still are having a hard time reaching… and 8" rod with a 6" stroke will only leave you with a 1.33 rod ratio.
What is the most efficient normally aspirated engines of today? In reference to this discussion I think we can say NHRA Pro Stock engines are quite impressive. Now, one of these would not be a particularly good choice directly out of the race car unless we make some changes to utilize the power. One change would be moving to a gear box or another would be change of components. Why? To utilize the power band (RPM range). As has been mentioned in threads, these things make their peak power over 9000 rpm. Let's observe what is going on in these peak efficiency engines that may not be particularly designed for long service life with their light weight parts and the aggressive cam designs resulting in short valve spring and lifter life, etc. But this thread started out about what accelerates an engine… Look at the parts for a 500" Pro Stock. Now, everyone is not going to tell you what they are using, but just observe the parts that are being sold by Pro Stockers in the back of National Dragster, etc. Now with statements by several major engine builders saying "we don't care about the rod ratio". Well, let's look at their engine… Now these are just out of the air figures for thought… Let's say the deck is short… 9.200 range and the stroke is in the range of 3.625… and with the thin rings and the ring package high in the piston.. lets' say a compression height around 1.265… well, we could just hook up the parts with around a 6.125 rod. This would give us about a 1.69 rod ratio…. Which may not be considered the best from the mechanical point of view, but not particularly bad and look at the other side of the air pump!!! Look what it does for the FLOW PATH!!! A straighter shot at the cylinder and now the intake and cylinder head can be used for maximum efficiency…. The induction system is where a lot of power and acceleration is made. Along with all this comes the shorter piston skirts, light ring package, short rods, small crank counterweights and small bearings which are LIGHT WEIGHT, lower drag, and reduced windage in their own right assist in acceleration. Have you seen the oil pan on a wet sump Comp Eliminator? Big boxes with small amounts of oil in the sumps….. Remember above… we need to keep the entire engine use in mind when considering design. Look at the DRCE III block…. Hmmm… short deck potential, big bore potential, large journal camshaft, additional camshaft support….

[Gearhead]

Induction System…. I'll try to be a little briefer in this post which actually is the one that is the most important. When Grumpy Jenkins published his Chevrolet Racing Engine book back in 1976… he first began with the detail of the block assembly. Then he came to the chapter on cylinder heads, and I am paraphrasing he said… we have spent all this effort on detailing the short block which good to bad may be 15 to 20 hp and now we are working on the heads which good to bad could be 100 hp. Basically…. Don't skimp on the top end!!! Again the overall use is the key in selection. Back in '76 there was little selection and now you can just about order any size head for any size engine and rpm that will work decent right out of the box. Too big a port will kill the velocity of the intake tract and conversely too small will restrict the engine. Now which one is best for you? That is the big question. Dynomation is a technical computer simulation that assist in engine design. There no easy plug and play program that can truly simulate your application, but some of these programs help. One fairly easy to use program that I like is Pipemax by Larry Meaux of MaxRace Software. Larry is an engine builder as well as a programmer. One feature I like is the Peak Demand of the port. Generally the peak demand occurs around 75 degrees after TDC in the induction cycle. This is a critical point on a maximum effort engine. To find where you are, you need to know the point of lift of your valve at this degree of rotation and the flow of your port to see if you may have too large a port or too small. Then you can work with induction and cam timing to reach a goal.
Again, I'm not the expert. Get with a reputable engine builder or cylinder head manufacturer. This stuff is for though stimulation and discussion. What trends have you seen in the cylinder heads over the last 20 years and particularly the last 5? On big blocks we have seen the advent of the Pontiac, Raptor and a few other heads. In NHRA Comp Eliminator using small blocks we have seen the big rage over angle of the valves in the heads. What is the deal? Do you notice the tipping of the valve angles? What is this doing? FLOW PATH…. Some of it is increase in airflow, some increase in the flow under the curve, quality of flow and chamber entry. What is this swirl and tumble all about? Swirl might be great for your low rpm street car trying to get maximum fuel efficiency, but it is not particularly good for high rpm maximum effort racing engines. On a flow bench if you are observing both swirl and flow… you reach a point where the flow stagnates and guess what…. Swirl goes crazy! The tipped angles definitely lower the swirl…. I was visiting with a major Pro Stock cylinder head manufacture/developer at the PRI show some 6 or 8 years ago and he said he had two heads with the same flow rates. One of them had less swirl…. And it ran faster down the track. The engine accelerated better……… I think I have put out plenty of air for awhile… As per Steelcomp's hope… all I want to do is stimulate conversation with open minded boaters.

[cstraub]

Gearhead, excellent posts. Your mention of Flow Path is interesting because just a few weeks ago I was discussing some stuff with someone and he had read some stuff out of Europe that stated the cam was nothing more then a mechanical way to make a Valve Path. An if you think about it. . .it makes sense.
To continue this I will start at the bottom. The oil pan. If you had told me 15 years ago there was power in an oil pan I would have have said "Yeah right". Well it was proved to me during some testing of a 2.0 Liter Ford Engine. While on the dyno this road race engine had a stock type pan on it. It was having some crank case pressure issues. The stock pan was taken off and modified with a large kickout, a scraper, and some screening. With nothing more then this the engine picked up 12HP. Huge gain for this thing.
The windage caused from the movement of the rotating assembly needs area to occupy. Now since the windage creates greater pressure, we need more area so that windage created will equalize; note this picture on the bottom of the page:
http://www.stefs.com/catalog/p02stefsapproach.pdf
The high pressure side is moved to the kickout side creating a low pressure side. By doing so the resistance on the crank to do work is reduced allowing it to work easier.
In Nascar we have strict size rules to oil pan dimensions. If we didn't oil pans would be from frame rail to frame rail in size.
So. . .and let me say this . ..if you are a class racer and every ounce of power is needed this whole thread will be of interest but if you are a pleasure boater it will be just good conversation.. . .So selection of a crankshaft with profiled counterweights to reduce windage is critical. Once chosen a well thought out wet or drysump pan must be utilized to control windage through out the operating range of the engine. By doing so acceraltion will be increased.

[cstraub]

Gearhead touched on weight so I will go there next as we go up the engine. I have spoke about Jager rods before. I may have posted this on hear but they are what is referred to as transformed aluminum into what Jager calls Alumini. A 6" Jager rod can weigh in the 415gm range. Very light. Does light make power, apprently yes;
In an IHRA Prostock engine program Jagers rods replaced the Ti rod being used. Weight reduction was around 110 gms per rod. So 880 grams were taken off the assembly. The engine was rebalanced and put on the dyno. An average gain of 35HP was obtained in the the powerband of the engine with the peak gain being 50HP. Engine quickness was also increased meaning the time to reach the operating range was shorter hence the engine was quicker. Reduction of weight in the RIGHT areas, let me repeat that the RIGHT areas can increase power and the ability to accerate.
In another case a set of rods was replaced in a Quick 8 door car. No dyno testing was done but track results for the combination posted quicker times with just the rod weight reduction change.
It has also been rumored that Jager built a 24 to 26lb aluminum crank for a Pro Stock team that runs the "500" inch class. The crank in addition to 400 gm rods and 380gm pistons ( mind you this is a dome piston in the range of 4.600 ish bore) were used to dominate the class during the spam of 12 months. By mid season of the second year the parts were deamed "illegal" by the sanctioning body. To add some more to the pot, the rod to crank pin clearance for oil was .0005". . . yeah thats right. . . .0005" There was no bearing.
Do you think Lance Armstrong would be competitive if he had another 75lbs on his frame?
Do you think the "Thorpedo" would have done what he did in the pool in Sydney if he had 50lbs on his frame?
Yeah weight reduction in the RIGHT areas does help acceleration.

[steelcomp]

Now we're getting somewhere!! Thanks Gearhead! :D :D That was a lot of typing, and a lot of good info. That must have taken you a while. Same goes for you, Chris. I'm going to read these posts a few times, as there's a lot of info. I'm sure there are great discussion points to be found here...I'll do my best!
Class is now in session. :D

[steelcomp]

Steelcomp, I just had the chance to go back and scan the thread that included the rod ratio comment copy of DM and apologize for posting some of the same old stuff again. One of the post in the thread from cstraub69 when he was at PRI visiting with a drag race engine builder that was considering building road race engines reminded me of a story from a camshaft development session we attended in Detroit about ten years ago. Prior to looking at the actual cam designs, the sessions spent quite a lot of time in the design and matching all the other related components for the intended rpm use. We studied the wire size, number of coils, materials, etc and the mathematical harmonics of the spring and at what RPM this takes place. Presently a SpinTron is utilized to study these relationships in running engines.
Anyway, after the long study of spring, camshaft rates and rpm relationship where the design desire was maximum power while controlling the valve train for longevity, the question was asked by the instructor, "Do we have any drag race engine developers in the group", to which three of us acknowledged. He then stated, "Well, you guys can throw a lot of our study out the window! We have been studying controlled valve trains and inductions and you guys deal in what we refer to as "CONTROLLED DESTRUCTION!"…".
Now I need to apologize for what I have provoked. I asked you in a previous post if there were any threads along some of the relative lines of engine development with port velocities and/or the effects of swirl in the combustion chamber and acceleration on a max performance high rpm (max efficiency) engine? Or the affects on acceleration using lighter weight components in the bottom end?
I apologize because this can become a very long post, even for general discussion purposes. I think I'll break this up into three related post so that it will be easier to respond. I am going to try and keep these post in as general terms as I can and not get into difficult to understand. These thoughts are not absolutes… just some info to promote discussion. I am not the expert.
First, no apology necessary, on any of this suff. I opened this thread hoping to open a "higher level" of discussion, and get a little deeper into what makes an engine work. Your responses are exactly where I was hoping all this would go, and I am greatful to have you here. I can (and do) "parrot" a lot of high tech stuff, with a fiarly good understanding of what's being discussed, but I realy don't "know" much of anything (in comparison), having not had as much hands on experience as someone such as yourself, or Chris, or a lot of the other guys here. I know in the past few years there's been an explosion of super hi tech information in engine development, but there's still the basics that need to be understood before any of that's of any use. I'm hoping these discussions will help myself, and others that might be interested, better understand why different engines do what they do.

[UBFJ #454]

Steve -
You say: "Class is now in session." Shouldn't that be 'Race Engine Building Class is now in session'?
In your initial post you asked the question: "What is it about an engine that makes it accelerate? Why does one engine accelerate better, or faster than another comparable engine from point A to point B?" So far the focus of everything here to date has been engine oriented ..... nothing has been said about drive trains/propulsion systems as engines don't accelerate between points A and B without being hooked to something to move them.
I bring this up because I believe far too often people get caught up with building the 'Best Engine', sometimes very expensive ones, and either totally ignore how it fits into the total scheme of things or don't got into the detail of deriving a comprehensive understanding of the total race vehicle system.
In my mind, the believe that 'Hp Is Everything' is wrong. My belief is that while Hp is certainly an integral component in a competitive racer, it is far more important that the efficient, most effective application of that Hp be accomplished ..... to accomplish that, you have to understand each of the components of the total system and how to build/'tune' each of them Individually & Together.
Having said that why not continue with engines ... then move on to the other components of race boats ... then how the total system of individual components should be made to work together.
Just a suggestion.

[cstraub]

Bear your "Dead On". Case in point with circle track, I'll will ask them if they can flat foot it around the track and 99% of the time they can't. So I tell them to get with their chassis guy and when they can, then the engine can be looked at.

[Gearhead]

I'll pitch in and say Bear & Chris are right on! As Bear relates the total package - Engine through drivetrain - Example: Comp Eliminator powerglide transmission... lightened planetary, roller bearings, not to mention the plethora of torque converter designs, etc. Rear end - lightened ring gears, rifle drilled axles - use of lower drag housings such as the 12 bolt Chevy drop in for a 9" Ford Case. The 9" drop in case is strong and easy to change gear ratios and service by easy removal, but the 12 bolt has a higher efficiency due to the intersection point of the pinion with the ring gear... so aftermarkets came up with the 12 bolt gear set in a pumpkin to drop in a 9 bolt housing.
Hmm... now how does that relate to my jet?
P.S. - Chris, I had a dirt track customer last year that his primary goals was not that of peak power. He desired a decent base tuneup, but then wanted to know the effects of timing changes on power output and restrictor spacers on power output so that he had a correlation of where to go when he needed to vary the power for track conditions..... ie... flat foot it and drive!

[MikeF]

Traction!
Just wanted to repost #9 on the list.
You can have all the HP in the world, but if you can't get it to the water/ground, it won't accellerate the quickest/fastest. :crossx:
Examples:
Hicks/Hottub, 5?? c.i., 6500+/-RPM, MPD pump, runs 7.50+/- in the 1/4 mile at nearly 140 mph.
JBG/BlingBling, 45? c.i., 9700+/-RPM, prop speed 11K+ w/ Grose CNC prop, runs 7.50+/- 1/4 mile, 140+ mph.
Two of the quickest (N/A) boats in the NJBA!
:)
A little off topic, but relevent none the less!

[cstraub]

I'll pitch in and say Bear & Chris are right on! As Bear relates the total package - Engine through drivetrain - Example: Comp Eliminator powerglide transmission... lightened planetary, roller bearings, not to mention the plethora of torque converter designs, etc. Rear end - lightened ring gears, rifle drilled axles - use of lower drag housings such as the 12 bolt Chevy drop in for a 9" Ford Case. The 9" drop in case is strong and easy to change gear ratios and service by easy removal, but the 12 bolt has a higher efficiency due to the intersection point of the pinion with the ring gear... so aftermarkets came up with the 12 bolt gear set in a pumpkin to drop in a 9 bolt housing.
Hmm... now how does that relate to my jet?
P.S. - Chris, I had a dirt track customer last year that his primary goals was not that of peak power. He desired a decent base tuneup, but then wanted to know the effects of timing changes on power output and restrictor spacers on power output so that he had a correlation of where to go when he needed to vary the power for track conditions..... ie... flat foot it and drive!
Gear,
Set Goal. . .build combination. . .excute. . .. achievement. It's pretty simple but I see all to many times guys get caught up in the status quo and want to belong that they end up building a combination that is someone elses path of reaching their goal.
Right now on another board a guy is wanting to get suggestions for an engine for a 3200Lb car, 4 speed, that is limited to an 8" tire. He has a 454 block. The majority wants to put a 4.250" stroke in it and punch it to 4.310". I say put a 3.766" stroke in it and punch it to 4.350". Spinning tires off the line doesn't win races. My way of thinking is launch easy and role into the throttle, but hell I don't have race car so I don't know anything.
Okay back to acceleration. . . .

[cstraub]

Just wanted to repost #9 on the list.
You can have all the HP in the world, but if you can't get it to the water/ground, it won't accellerate the quickest/fastest. :crossx:
Examples:
Hicks/Hottub, 5?? c.i., 6500+/-RPM, MPD pump, runs 7.50+/- in the 1/4 mile at nearly 140 mph.
JBG/BlingBling, 45? c.i., 9700+/-RPM, prop speed 11K+ w/ Grose CNC prop, runs 7.50+/- 1/4 mile, 140+ mph.
Two of the quickest (N/A) boats in the NJBA!
:)
A little off topic, but relevent none the less!
No Mike your on topic. Can you hook it? What good is a 800HP big block if you can't put to the water. . .dirt.. .or asphalt. It's no good, because the guy with 500HP is going to pass you because he has it all working for him.

[cstraub]

Remind me once we get into the heads and induction to talk about Ram Effect, I was just reminded I said I would do this on another thread and didn't.

[Gearhead]

Gear,
Right now on another board a guy is wanting to get suggestions for an engine for a 3200Lb car, 4 speed, that is limited to an 8" tire. He has a 454 block. The majority wants to put a 4.250" stroke in it and punch it to 4.310". I say put a 3.766" stroke in it and punch it to 4.350". Spinning tires off the line doesn't win races. My way of thinking is launch easy and role into the throttle, but hell I don't have race car so I don't know anything.
Okay back to acceration. . . .
Chris,
I like the way you think.... Lots of lower RPM torque in a stick car and an 8" tire!!! Unless he has one heck of a chassis he will enjoy a lot of white smoke from the tires! The 4.25 would be good for the jetboat but in my opinion not too good for the limited tire car.
Now your alternate idea holds merit. Comp Eliminator A/ED .... 440" to 460" range... using 4.5 to 4.6 or larger bores... 3.4 to 3.6 strokes... 12" to 14" tires sub seven seconds... With the short stroke the engines don't have monstrous torque down low, but they sure do RPM and make HP down track!
Gearhead

[cstraub]

From combo meals to houses we just are taught bigger is better while in reality we need to worry about what we need things in moderation. I'm not the most religous person but I believe in moderation.

[UBFJ #454]

"Hmm... now how does that relate to my jet?"
Hmmm ..... Now that's a subject worth its own Thread that could also be very interesting. Gearhead, why don't you start a thread to discuss that topic in the 'Jet Section'?

[steelcomp]

"Hmm... now how does that relate to my jet?"
Hmmm ..... Now that's a subject worth its own Thread that could also be very interesting. Gearhead, why don't you start a thread to discuss that topic in the 'Jet Section'?
Bear, you can bet every bit of it applys to your jet, in one way or another. The point is, as you posted earlier, there's no one thing that makes an engine better or worse...it's alwyas the best combination. The trick is in learning as much as possible about each componant, knowing how they effect eachother, and how to combine their qualities (or avoid their flaws) to achieve your goal. Obviously, the higher the goal, the more you have to know...or pay someone who does!
Chris and Steven. Are you having fun?
Smart guys. :rolleyes: LOL!
OK...where I'd like to start, is in the combustion chamber. In a four stroke engine, there's only one power stroke, and like someone posted on another site, the other three strokes are just hindering it. Flow as much as you want, lighten everything you can, cam it, ram it, slam it, but unless you know what's going on and how to optimize the burn, it's all just spinning metal, creating nothing.
What goes on in the chamber? Why does gasoline detonate? How have chambers evolved to maximize burn? Can we talk about things like compression ratio, swirl, tumble, quench, etc? To me, this is the heart of the matter, and where the power is made...or not.

[steelcomp]

Gearhead:Look at the parts for a 500" Pro Stock. Now, everyone is not going to tell you what they are using, but just observe the parts that are being sold by Pro Stockers in the back of National Dragster, etc. Now with statements by several major engine builders saying "we don't care about the rod ratio". Well, let's look at their engine… Now these are just out of the air figures for thought… Let's say the deck is short… 9.200 range and the stroke is in the range of 3.625… and with the thin rings and the ring package high in the piston.. lets' say a compression height around 1.265… well, we could just hook up the parts with around a 6.125 rod. This would give us about a 1.69 rod ratioIn 1998, Larry Widmer wrote a response to a question asking for a description of a Pro Stock engine build, which I have read, and it's very detaialed. One thing I noticed was that he chose a particular rod ratio to start, and let everything work from there.
Larry Widmer:This is where the package height starts affecting everything we do. Since I attempt to run a rod length to stroke ratio of 1.75 - 1, calculating the rod length combined with the compression height(distance from pin C/L to deck), and (.5 x stroke) will yield our block deck height once we settle on the stroke. The combination using 4.6" bore, and 3.75" stroke, with a 6.5" rod, and a piston with a 1.265" compression height will yield a deck height of 9.635"and the rod length to stroke ratio will be 1.73 -1 which is "good". Since you were good enough to give your input, I thought I'd offer another view on geometry, and the importance of rod ratio. So much so that he was willing to allow his package be designed around it. Maybe thigs have changed since then, but that's a littel different than "the rod's just a device that connects the crank with the piston" theory. Larry's pretty sharp.

[MikeF]

In a N.A. application, focus should be on getting the maximum charge into the combustion chamber/cylinder 1st. With only suction (and resulting waves) being the only motivator for the action to happen, it is difficult to pull the mix into the cylinder. You would want the pull to be as great as possible. How do we keep that moving forward to fill it best?! :boxed:
Pushing the now lighter gasses out is taken care of by that moving wall called a piston. It's got to go somewhere.
I was looking for some 3 valve heads that I've seen in the past (2 in,1 ex), but I did not locate ones for a bbc. There are however some on the barrygrant site for some sbc ones.(they do not show the rocker side of the head) Also Jim Feuling had some heads he designed awhile ago w/small figure 8 style chambers but that website is now gone too. I know I've got pics somewhere.

[UBFJ #454]

Let's keep this Thread going ... How about some discussion of N/A motor header design and how you can gain Hp there ... stepped header design, primary tube lengths, etc..

[cstraub]

Bear,
When it come to combustion I am not that well versed except for some basic knowledge and a few tricks so I really don't feel I am qualified. Steelcomp may want to e-mail Larry Widmer and see if he would come on and "type" some. If not a link to his site on combustion may be a good deal.
After that we can tackle the stuff above the deck surface. I would invite any of the machinest on here to share tolerances and stuff like that they feel help contribute to an engines performance.

[HOSS]

I usually through a bunch of gas at em and they just seem to work good.
I really love what one guy told me about having 235 in the hole and being at 9.5:1. If he is then half the charge is going out the exhaust. Must be shootin flames.

[cstraub]

I am going to try and get French Grimes to post something on combustion here. In the mean time lets move on to heads: Who wants to start? Does Velocity or Volume win races?

[Squirtin Thunder]

I am going to try and get French Grimes to post something on combustion here. In the mean time lets move on to heads: Who wants to start? Does Velocity or Volume win races?
Wouldn't it be the velocity of the volume witch does the work ???

[cstraub]

Wouldn't it be the velocity of the volume witch does the work ???
Yup.

[Infomaniac]

I'm curious about that single power stroke that is doing the real work. How much of that stroke is actually utilized?
I read somewhere years ago in my quest for info that once the crank reaches 90 degrees ATC of the power stroke, all the torque has been delivered by the crank so you might as well open the exhaust valve.
Thoughts?

[steelcomp]

What do you think would happen if you opened the ex valve 90* ATDC??

[steelcomp]

I am going to try and get French Grimes to post something on combustion here. In the mean time lets move on to heads: Who wants to start? Does Velocity or Volume win races?
Velocity, up to a certain point, is a good thing. To what point depends on the port and intake shape(s). I think volume is going to be dictated by the velocity, and the MCSA of the port, if we're talking about just the head.
I'm going to email Larry. :D

[rmbuilder]

I'm curious about that single power stroke that is doing the real work. How much of that stroke is actually utilized?
I read somewhere years ago in my quest for info that once the crank reaches 90 degrees ATC of the power stroke, all the torque has been delivered by the crank so you might as well open the exhaust valve.
Thoughts?
Info,
Eighty percent of effective power is delivered to the arm in the first twenty percent of the power stroke. By 90* ATDC there is very little useful energy being transferred. Near this point (depending on the cylinder pressure map) the remaining cylinder pressure is better utilized in blowing down the cylinder rather than trying to extract additional power. By opening the exhaust valve (BBDC) the remaining cylinder pressure is > the pressure in the exhaust tract as the pulse exits. As the pressure excursion purges the cylinder, evacuating the residual gasses, the cylinder pressure begins to equalize. When the piston reaches BDC, the chamber is near equalized, and very little work must be done to expel the remaining gasses (on the exhaust stroke) greatly reducing pumping losses. The earlier EVO allows for the exhaust valve to begin opening sooner generating greater lift (sooner) during the exhaust stroke. Below is the timing card for the Crane 168771 cam
302*/308* @ .004”
240*/248* @ .050”
.621”/.632”
The EVO is 90* BBDC / ( 90* ATDC)
http://www.cranecams.com/index.php?show=browseParts&action=partSpec&partNumber=168771&lvl=2&prt=5
The more common Crane 168741 has an EVO of 86* BBDC or, 94* ATDC.
Bob

[Infomaniac]

Info,
Eighty percent of effective power is delivered to the arm in the first twenty percent of the power stroke. By 90* ATDC there is very little useful energy being transferred. Near this point (depending on the cylinder pressure map) the remaining cylinder pressure is better utilized in blowing down the cylinder rather than trying to extract additional power. By opening the exhaust valve (BBDC) the remaining cylinder pressure is > the pressure in the exhaust tract as the pulse exits. As the pressure excursion purges the cylinder, evacuating the residual gasses, the cylinder pressure begins to equalize. When the piston reaches BDC, the chamber is near equalized, and very little work must be done to expel the remaining gasses (on the exhaust stroke) greatly reducing pumping losses. The earlier EVO allows for the exhaust valve to begin opening sooner generating greater lift (sooner) during the exhaust stroke. Below is the timing card for the Crane 168771 cam
302*/308* @ .004”
240*/248* @ .050”
.621”/.632”
The EVO is 90* BBDC / ( 90* ATDC)
http://www.cranecams.com/index.php?show=browseParts&action=partSpec&partNumber=168771&lvl=2&prt=5
The more common Crane 168741 has an EVO of 86* BBDC or, 94* ATDC.
Bob
Thanks Bob,
That was my point with the question. Only 1 stroke really doing any work and of that stroke only a fraction of it. For sure only half of it if the exhaust valve opens around 90 degrees.
If you look at a degree wheel. Typical exhaust opening range is 100 degrees BBDC to 60 degrees BBDC. 80 degres ATDC to 120 degrees ATDC
How ineffecient of a design huh?
So what are the best ways to optimize that short event period?
And .... If for some reason cylinder pressure could be extended beyond the 90 degrees, how much useful work would it be doing?

[steelcomp]

So what are opening and closing events of an ex lobe based on? How does this affect an engine's acceleration?

[steelcomp]

If you look at a degree wheel. Typical exhaust opening range is 100 degrees BBDC to 60 degrees BBDC. 80 degres ATDC to 120 degrees ATDCat what lift is this? .006? .020? .050?
How ineffecient of a design huh? When you look at it that way, yes it is.
So what are the best ways to optimize that short event period? Create the most effecient combustion process.

[steelcomp]

The earlier EVO allows for the exhaust valve to begin opening sooner generating greater lift (sooner) during the exhaust stroke.
This is true with most "average" ex ports. This is why I'm an advocate of having the best exhaust port possible. It would be great if the ex port could flow the same as the intake port. You wouldn't have to open the ex valve so early or lift it as high. You could take advantage of the remaining pressur in the cyl, and still evacuate effeciently. The remaining pressure in the cyl past 90* is still pushing down on the piston, and anything is better than nothing.
For example:
The ex lobe in my 467, with the Canfields that I ported is opening (@.050) 69 BBDC, and closing 17 ATDC. That's a long way from the numbers you're talking about, but the ex port on those heasds flowed 298 @ .700, and 312 @ .800. That's over 85% of the intake at the same lift. The results speak for themselves. That engine also made BMRP #'s in the high 190's and broke 200 @ peak torque. That's with only 12.4:1. Good combustion.
RMbuilder...what you quoted is true to a certain extent, on certain motors, but is also a very wide and sweeping generalization.

[Infomaniac]

This is true with most "average" ex ports. This is why I'm an advocate of having the best exhaust port possible. It would be great if the ex port could flow the same as the intake port. You wouldn't have to open the ex valve so early or lift it as high. You could take advantage of the remaining pressur in the cyl, and still evacuate effeciently. The remaining pressure in the cyl past 90* is still pushing down on the piston, and anything is better than nothing.
For example:
The ex lobe in my 467, with the Canfields that I ported is opening (@.050) 69 BBDC, and closing 17 ATDC. That's a long way from the numbers you're talking about, but the ex port on those heasds flowed 298 @ .700, and 312 @ .800. That's over 85% of the intake at the same lift. The results speak for themselves. That engine also made BMRP #'s in the high 190's and broke 200 @ peak torque. That's with only 12.4:1. Good combustion.
RMbuilder...what you quoted is true to a certain extent, on certain motors, but is also a very wide and sweeping generalization.
@.050 is not where the valve opens. It has been open for .050 of lift at that point. And the cam is turning 1/2 of crank speed.
What does exhaust valve opening have to do with acceleration? Just one of the events involved with the amount of push on the piston.
Isnt that one of the directons this thread has gone? Every post has not addressed the initial question.

[Infomaniac]

Create the most effecient combustion process.
Effecient as far as?
Mechanical?
Thermodynamic?
The most power with the least amount of fuel is going to make the engine accelerate more/faster?
How about the most powerful combustion process regardless of how much fuel is used.

[steelcomp]

Effecient as far as?
Mechanical?
Thermodynamic?
The most power with the least amount of fuel is going to make the engine accelerate more/faster?
How about the most powerful combustion process regardless of how much fuel is used.
Mechanical. Thermodynamic is less an issue, although there's also debate about that. (Alum vs. cast iron heads, coatings, etc.)
Effecient dosen't necessarily mean with the least amount of fuel, to me, it means creating the best burn possible with whatever fuel you're using. The engine's effeciency (BMEP) is going to determine how much power it makes, not necessarily it's fuel consumption, although they are related. This is why I feel that the chamber, and relationship between the chamber and piston is as critical, if not more critical than any other area of focus. Too bad most guys just buy pistons off the shelf and figure that's the best they can do, without really understanding what's going on in the chamber, and in the cyl. as it fills, before compression. It's the burn that makes the power. Nothing else.
The most power with the least amount of fuel is going to make the engine accelerate more/faster? I think you'll find that an engine that will accelerate it's best can very well use less fuel than one that dosent accelerate as well, and it's certainly going to need fewer pit stops.

[Moneypitt]

[quote]I think you'll find that an engine that will accelerate it's best can very well use less fuel than one that dosent accelerate as well, and it's certainly going to need fewer pit stops.
Sounds like a plan for the next Parker enduro, have you got plans to run???MP

[steelcomp]

[quote]I think you'll find that an engine that will accelerate it's best can very well use less fuel than one that dosent accelerate as well, and it's certainly going to need fewer pit stops.
Sounds like a plan for the next Parker enduro, have you got plans to run???MP
I may be driving, but nothing of my own. Just too many projects this year.

[rmbuilder]

This is true with most "average" ex ports. This is why I'm an advocate of having the best exhaust port possible. It would be great if the ex port could flow the same as the intake port. You wouldn't have to open the ex valve so early or lift it as high. You could take advantage of the remaining pressur in the cyl, and still evacuate effeciently. The remaining pressure in the cyl past 90* is still pushing down on the piston, and anything is better than nothing.
For example:
The ex lobe in my 467, with the Canfields that I ported is opening (@.050) 69 BBDC, and closing 17 ATDC. That's a long way from the numbers you're talking about, but the ex port on those heasds flowed 298 @ .700, and 312 @ .800. That's over 85% of the intake at the same lift. The results speak for themselves. That engine also made BMRP #'s in the high 190's and broke 200 @ peak torque. That's with only 12.4:1. Good combustion.
RMbuilder...what you quoted is true to a certain extent, on certain motors, but is also a very wide and sweeping generalization.
Steelcomp,
In my conversation with Infomaniac we were both referencing the valve events at rated seat duration. As correctly stated by Info, referencing the valve timing @ .050” is of no value here as the valve is already well off the seat at .050” lifter rise. This is particularly significant with the EVO as the pressurized cylinder begins to blow down immediately as the valve begins to open. Given there is still some residual cylinder pressure remaining in the power stroke @ 90* ATDC the balancing act then becomes determining at what point the decaying pressure curve is best utilized to blow down the cylinder vs. where it delivers useable leverage to the arm. In your rebuttal you referenced many significant data points particular to your engine. Looking at your exhaust lobe let me quote you
“opening (@.050) 69 BBDC, and closing 17 ATDC. That's a long way from the numbers you're talking about,”
You referenced the .050” (266*) exhaust timing numbers here with an EVO of 69* BBDC. To examine your exhaust lobe correctly @ rated seat duration (as per my previous post) we need to utilize your correct exhaust lobe dimensions, which are (302* rated). Given your centerlines this will render a rated seat EVO (lash factor included) of 87* BBDC/ 93* ATDC which are 1*-3* of the valve events Ron and I were discussing, hence my confusion with your last sentence. What I quoted is true, in reference your motor, and is in no way “a very wide and sweeping generalization.” The laws of physics do not discriminate.
Bob

[steelcomp]

Anyone interested in re-opening this discussion?

[Warp Speed]

After taking a quick look at this thread, this should get pretty interesting!! :idea:
Warp Speed ;)

[cfm]

Pressure.

[fc-pilot]

God allows it to accelerate.
Paul

[centerhill condor]

Money! like the guy said back in '05! Especially with the price of gas!
CC

[steve d]

.............When the build was off or it was a little tired...........CH3NO2

[gn7]

oh steel, did you really need to open this can of worms again! I stayed out of it the first time but.............. well here goes. According to Newton if something moves it means a force acted apon it. and torque is a force.
But Fulton (the father of horsepower) says the speed at which it moves is the result of horsepower. Torq can move something with zero regards to time, horsepower is totally time based. You asked about accell so the answer is HP

[snake321]

What's going on???
I was downloading Desktop Dyno and it linked me to here....

[steelcomp]

After taking a quick look at this thread, this should get pretty interesting!! :idea:
Warp Speed ;)Love to get some of your input here, Warp. Maybe we can get Steven (gearhead) to chime back in.

[steelcomp]

God allows it to accelerate.
Paul:D

[MACHINEHEAD]

Pressure differential

[steelcomp]

Pressure.That's definately the beginning. Without 14.7psi, we're no where.
C'mon guys, this was a good thread and it just died. Something more than "what carb should I run"... :D

[steelcomp]

Pressure differentialFrom where to where?

[MACHINEHEAD]

I like these kinds of talks but, we are usually stuck with the parts that are given by manufactures. And the budgets given by customers. And the amount of time to get an engine running. Not trying to be a downer but what are we going to do when we all decide that there is a really good combo, but it needs special lenth/weight/size parts. We will comprimise! And try to get the closest thing made or off the shelf. Then you will be left walking the halls at night, puffin' a fattie and thinking what if. Not me. If its not huffing nitro and burning off 16 spark plugs in 5 seconds its a comprimise! But I really do like engine tech.

[steelcomp]

I like these kinds of talks but, we are usually stuck with the parts that are given by manufactures. And the budgets given by customers. And the amount of time to get an engine running. Not trying to be a downer but what are we going to do when we all decide that there is a really good combo, but it needs special lenth/weight/size parts. We will comprimise! And try to get the closest thing made or off the shelf. Then you will be left walking the halls at night, puffin' a fattie and thinking what if. Not me. If its not huffing nitro and burning off 16 spark plugs in 5 seconds its a comprimise! But I really do like engine tech.But what if...what if you cold design your own ports, your own chambers, your own piston domes and your own intake runners. What information goes into that kind of thinking? I've read so much of Larry Widmer's stuff, where he had the cpapbility to do those things, and I always wondered, where do you start? I know---picking a goal, but after that? What if you had a clean sheet of paper.

[thatguy]

Old...yes, this is all about acceleration over time, since we're trying to get from point A to point B in the least amount of time as possible. Increasing velocity is increasing acceleration, etc, but that's symantics AFA my question.
What makes an engine accelerate? Your second paragraph touches on where I think this will eventually go.
Busby, in his not-so-eloquent terms says it's the short rod that helps. (I'll get back to you and your short jokes later, pal.) There's too many other things to consider to say that the rod ratio by itself is going to "make" an engine accelerate or not. But where's the motivation coming from? I'm thinking more in terms with what's going on in the combustion chamber. Good burn vs. better burn, vs. best burn. In this sense, Daryl Morgan may have a point.
Not if the drive mechanism is engaged at a higher RPM.
I haven't read past here yet, so I am sure I am missing alot. But decreasing rod ratio (longer rod) also is mechanically "easier" on the rotating assembly (less side loading), therefore alowwing higher, and quicker, rpm potential. Is it not?
Tommy

[sangervdrive]

I have enjoyed reading this thread from start to here, but have little to add.
The most interesting thing I am left with is the comment about making the ex port flow as good as the intake port.
It is my nature to say why shouldn't it flow as good. Should that be so difficult to acheive? Doesn't seem like it. In fact it seems quite logical that if you had a room with two doors and your objective was to move people through the room, why would you make the out-door smaller than the in-door??
It seems to me that through the progression of engine building everyone was probably focused on getting more into the chamber and thinking "the exhaust port doesn't matter, it gets pushed out by the piston." That seems very wrong to me.
I also like the idea of waiting as long as possible for EVO so as to utilize the pressure as much as possible but around 90 ATDC wouldn't the piston be moving so fast that it would nearly make that small amount of pressure a mute point. It seems more important to make it easier for the piston to come back up at that point than try to "beat the dead horse" of the then used up combustion.
By the way I am pretty close to being at rock bottom (knowledge-wise, and have a large appetite to learn more. I have 3 or 4 big block books but would be open to any suggestions.

[MACHINEHEAD]

Hot, spent gasses have less volume or mass or whatever you want to call it. So the door does not need to be as large. Usually on a good head, average exhaust to intake flow ratios are about 70 to 80%. Also take into consideration that all modern engines have more intake area than exhaust area. Secondly, cam manufacturers all have very close to the same timing events,across the board, for a reason, it works!

[steelcomp]

Not if the drive mechanism is engaged at a higher RPM.
I haven't read past here yet, so I am sure I am missing alot. But decreasing rod ratio (longer rod) also is mechanically "easier" on the rotating assembly (less side loading), therefore alowwing higher, and quicker, rpm potential. Is it not?
Tommy
I've read a lot of pros and cons on rod ratio and IMO the outcome is that the majority (not all) of the more successful engine designers/builders will state that what you said above is correct. Longer rod = increasing (numerically) rod ratio.
Wow...I just saw a typo in that quote of mine...did I actually write Daryl Morgan?? Jeezzz!:rolleyes:

[steelcomp]

I have enjoyed reading this thread from start to here, but have little to add.
The most interesting thing I am left with is the comment about making the ex port flow as good as the intake port.
It is my nature to say why shouldn't it flow as good. Should that be so difficult to acheive? Doesn't seem like it. In fact it seems quite logical that if you had a room with two doors and your objective was to move people through the room, why would you make the out-door smaller than the in-door??
It seems to me that through the progression of engine building everyone was probably focused on getting more into the chamber and thinking "the exhaust port doesn't matter, it gets pushed out by the piston." That seems very wrong to me.
I also like the idea of waiting as long as possible for EVO so as to utilize the pressure as much as possible but around 90 ATDC wouldn't the piston be moving so fast that it would nearly make that small amount of pressure a mute point. It seems more important to make it easier for the piston to come back up at that point than try to "beat the dead horse" of the then used up combustion.
By the way I am pretty close to being at rock bottom (knowledge-wise, and have a large appetite to learn more. I have 3 or 4 big block books but would be open to any suggestions.I'm a big fan of good exhaust flow...as much as you can get (I think I posted this earlier in this thread) No reason not to. The better the port, the less you have to lift the valve, the easier it is on springs and rockers, and that's always a factor in successful performance.
AF piston speed and the effects of pressure, that's where the arguement of rod length starts getting interesting. A short rod ratio can have the piston actually out-accelerate the flame front. That's why on something like an F1 engine, with their piston speeds, you see rod ratios near 2:1

[HIRED GUN]

mR. sTEELCOMP...YOU SHOULD ASK THIS ON S----TALK.COM....LOL

[steelcomp]

mR. sTEELCOMP...YOU SHOULD ASK THIS ON S----TALK.COM....LOLYeah, but then those guys get talking in languages and using words I don't even know!
Some way smart guys there.

[steelcomp]

OK...here's part of the original question for this thread. What makes an engine accelerate? With the carb at WOT, (or throttle body, or whatever) with no load, why does the engine just keep going faster and faster? What makes it increase in rpm? Even with a load, for that matter, but what makes it increase in rpm?
More air/fuel coming in, making more power? Or-
More power, making more air/fuel come in?
Which occurs first, and how does it effect the other?:idea:

[Budweiser]

I just spent the last hour or so reading all this, finally get to the end... and you ask what came first, the chicken or the egg??? WTF man??? The egg. Duh, I thought everyone knew that. ;)
OK now, really, I started to get intrigued when you brought up burn efficiency. I assume you're speaking of the science behind "fast burn" heads and such. Yeah, of coarse we all want to get the most air/fuel mix into the cylinder... You have a point! How, or what can we do to take full advantage of it's potential??? I am interested. I want to know! If we can extract more power from a given amount of air/fuel by design of the combustion chamber, pistons, etc. I'm all about learning more about it!

[Sleeper CP]

It seems to me that through the progression of engine building everyone was probably focused on getting more into the chamber and thinking "the exhaust port doesn't matter, it gets pushed out by the piston." That seems very wrong to me.
.
Hot, spent gasses have less volume or mass or whatever you want to call it. So the door does not need to be as large. Usually on a good head, average exhaust to intake flow ratios are about 70 to 80%. Also take into consideration that all modern engines have more intake area than exhaust area. Secondly, cam manufacturers all have very close to the same timing events,across the board, for a reason, it works!
Good answer Machinehead, but you already knew that. Most over 60% of exhaust gases are gone on "blow down" on the power stroke BBDC. When the exhaust valve cracks open the pressure in the chamber wants to get the hell out of there and it does. The rest of the exhaust stroke cycle removes the rest.
OK now, really, I started to get intrigued when you brought up burn efficiency. I assume you're speaking of the science behind "fast burn" heads and such. Yeah, of coarse we all want to get the most air/fuel mix into the cylinder... You have a point! How, or what can we do to take full advantage of it's potential??? I am interested. I want to know! If we can extract more power from a given amount of air/fuel by design of the combustion chamber, pistons, etc. I'm all about learning more about it!
Fast burn chambers, quench , tumble or swirl aren't new idea's. Robert Yates first Nascar smblk ford head comes to mind. The Yates Ford C-460 BBlk head is a 65cc big block head that flows nearly 450cfm out of the box. With that small of a chamber you don't have a big dome to screw up flame front or cause hot spots. Burn efficiency is a very big part of it. I dont know if you read the thread on my 565" dyno day.
The current engine has a BSFC of .366 it burns less fuel per hour (17 gallons) acutally making 935 HP than the old engine burned making 855 hp with a BSFC of .48. Go figure:jawdrop: It makes 80 more hp and burns less fuel doing it.
There are a few reasons why, but the two big ones are: fast burn chamber in the heads and compression ratio increase 1 point 11.8 vs 10.8. My head guy re-shaped the combustion chamber and made it a fast burn swirl chamber. And the compression ratio increase add effecency that was being lost before.
Maybe more later I have to hit the sack... Good night.
Sleeper CP
Big Inch Ford Lover:D

[steelcomp]

Good answer Machinehead, but you already knew that. Most over 60% of exhaust gases are gone on "blow down" on the power stroke BBDC. When the exhaust valve cracks open the pressure in the chamber wants to get the hell out of there and it does. The rest of the exhaust stroke cycle removes the rest.
Fast burn chambers, quench , tumble or swirl aren't new idea's. Robert Yates first Nascar smblk ford head comes to mind. The Yates Ford C-460 BBlk head is a 65cc big block head that flows nearly 450cfm out of the box. With that small of a chamber you don't have a big dome to screw up flame front or cause hot spots. Burn efficiency is a very big part of it. I dont know if you read the thread on my 565" dyno day.
The current engine has a BSFC of .366 it burns less fuel per hour (17 gallons) acutally making 935 HP than the old engine burned making 855 hp with a BSFC of .48. Go figure:jawdrop: It makes 80 more hp and burns less fuel doing it.
There are a few reasons why, but the two big ones are: fast burn chamber in the heads and compression ratio increase 1 point 11.8 vs 10.8. My head guy re-shaped the combustion chamber and made it a fast burn swirl chamber. And the compression ratio increase add effecency that was being lost before.
Maybe more later I have to hit the sack... Good night.
Sleeper CP
Big Inch Ford Lover:D I believe it was Larry Widmer that was the brainas behind the "fast burn" head. He called it the "soft" head. They did a test on a 351C nascar type engine that had some unbelievable compression and they tried to detonate it. Kept throwing timing at untill you'd have thought the crank would bounce off the floor.
It never detonated.
The shape on the top of the piston has as much to do with what goes on in the combustion chamber as the chamber itself. With a flat top piston, you're only getting half the benefit of the fast burn head.
Widmer developed the Yates head for both Bill Elliott and Bob Glidden when they both were totally dominant in their sport.

[Sleeper CP]

I believe it was Larry Widmer that was the brainas behind the "fast burn" head. He called it the "soft" head. They did a test on a 351C nascar type engine that had some unbelievable compression and they tried to detonate it. Kept throwing timing at untill you'd have thought the crank would bounce off the floor.
It never detonated.
The shape on the top of the piston has as much to do with what goes on in the combustion chamber as the chamber itself. With a flat top piston, you're only getting half the benefit of the fast burn head.
Widmer developed the Yates head for both Bill Elliott and Bob Glidden when they both were totally dominant in their sport.
In the second Engine Master's Competition Jon Kaases' winning 460 had a welded up combustion chamber it was 17cc's. The camber was in top of the piston.
The "fast burn" chamber Geoff Mummert made in our A-460 head is an "apple" shape. Our combustion chamber is 66 cc's. The piston has a reverse dome "dish" and it still has 11.8:1 compression. The chamber design really helps on how the engine burns it fuel.
Sleeper CP
Big Inch Ford Lover:D

[thatguy]

OK...here's part of the original question for this thread. What makes an engine accelerate? With the carb at WOT, (or throttle body, or whatever) with no load, why does the engine just keep going faster and faster? What makes it increase in rpm? Even with a load, for that matter, but what makes it increase in rpm?
More air/fuel coming in, making more power? Or-
More power, making more air/fuel come in?
Which occurs first, and how does it effect the other?:idea:
As I see it, most of what you ask above is all symptomatic of what is really happening. When You punch it, WOT, the "acceleration" of the rpm's is what is physically necessary to reach the maximum RPM potential of the WOT condition.
If all laws of motion could be thrown out, as well as the variables such as friction and inertia, the engine would instantly be at max rpm as soon as your foot went down.
So it isn't what is "making" it accelerate. It's more what is "hindering" it from reaching the WOT condition.
Or not. :D
Tommy

[cfm]

Pressure differential
I said 'Pressure' a few posts above yours. LOL.
So pressure and pressure differential. I think we both rapped it up. LOL.
It's not just about Atmospheric vs in cylinder pressure differential, but in cylinder (combustion) vs in crankcase psi.
What does more air and fuel do ?
What does a more effecient combustion space do ?
What does more compression do ?
What does a larger bore and/or stroke do ?
What effects does ignition timing have ?
Even though there are a ton of different aspects to it, this whole question IMHO can be answered by one or two words:
Short version: pressure
Long version: pressure differential
Maybe a better version: pressure pulses (speaking about just comb chamber here)
The higher the pressure pulse and the more pressure pulses you can create per minute/second/hour/what have you - the more work will get done.
Doesn't provide for much talk though. LOL.
;;;;;;;;;insert bunch of smilies here;;;;;;;;;;;
Saying this all laid back and just havin fun.

[Hass828]

[QUOTE=cfm;2930330]I said 'Pressure' a few posts above yours.
Short version: pressure
Long version: pressure differential
I agree with CFM. If its all about flow and physics, then why does it accelerate-rev -torq - whatever, faster when you use NOS? answer-pressure.

[MACHINEHEAD]

Roger that CFM. My brutally honest father calls these kinds of "talks" yammering!:chi:

[steelcomp]

Roger that CFM. My brutally honest father calls these kinds of "talks" yammering!:chi:I'd say then don't bother. You and CFM are obviously way far ahead of everyong else here.

[steelcomp]

I said 'Pressure' a few posts above yours. LOL.
So pressure and pressure differential. I think we both rapped it up. LOL.
It's not just about Atmospheric vs in cylinder pressure differential, but in cylinder (combustion) vs in crankcase psi.
What does more air and fuel do ? Adds the piotential for more heat
What does a more effecient combustion space do ? allows a more effecient burn or combustion
What does more compression do ? Forces more air/fuel into a smaller area, and if properly homoginized, burns more effeciently and creates a better combustion
What does a larger bore and/or stroke do ? Larger bore aloows for better breathing by unshrouding valves, and also allows more surface area of piston top which can have positive and negative effects. Longer stroke offers more mechanical advantage for combustion to apply work to load.
What effects does ignition timing have ? Countless.
Even though there are a ton of different aspects to it, this whole question IMHO can be answered by one or two words:
Short version: pressure
Long version: pressure differential
Maybe a better version: pressure pulses (speaking about just comb chamber here)
The higher the pressure pulse and the more pressure pulses you can create per minute/second/hour/what have you - the more work will get done. Easy answer, but how do you create more "pulses" to get more work done?
Doesn't provide for much talk though. LOL. That's just because you're being lazy.:D
;;;;;;;;;insert bunch of smilies here;;;;;;;;;;;
Saying this all laid back and just havin fun. So what does crankcase pressure have to do with combustion pressure? Are you saying they're related, or just refering to crankcase atmosphere and it's drag on the rotating assy? That can certainly limit acceleration.
Pressure is the byproduct of combustion. Pressure is what does the work, but pressure, or the amount of pressure is directly related to the combustion process. That's what makes an engine accelerate. What ever goes on in an engine, the ports, the cam, the ignition,l the AFR, the shape of the chamber and piston dome, etc....all are in the effort to promote better and more effecient combustion.

[steelcomp]

[QUOTE=cfm;2930330]I said 'Pressure' a few posts above yours.
Short version: pressure
Long version: pressure differential
I agree with CFM. If its all about flow and physics, then why does it accelerate-rev -torq - whatever, faster when you use NOS? answer-pressure.How does NOS create more pressure?

[steelcomp]

As I see it, most of what you ask above is all symptomatic of what is really happening. When You punch it, WOT, the "acceleration" of the rpm's is what is physically necessary to reach the maximum RPM potential of the WOT condition.
If all laws of motion could be thrown out, as well as the variables such as friction and inertia, the engine would instantly be at max rpm as soon as your foot went down.
So it isn't what is "making" it accelerate. It's more what is "hindering" it from reaching the WOT condition.
Or not. :D
Tommy
:idea: :idea: So what can be done to reduce the effects of what's "hindering" it from accelerating? You mentioned the laws of physics. In a sense, there are two worlds that an engine has to deal with... internal, or the combustion process, and making it as good as possible, and external, which is as you say, the laws of physics, and what's physically hindering the engine from accelerating. Maximize one, and minimize the other.

[steelcomp]

I just spent the last hour or so reading all this, finally get to the end... and you ask what came first, the chicken or the egg??? WTF man??? The egg. Duh, I thought everyone knew that. ;)
OK now, really, I started to get intrigued when you brought up burn efficiency. I assume you're speaking of the science behind "fast burn" heads and such. Yeah, of coarse we all want to get the most air/fuel mix into the cylinder... You have a point! How, or what can we do to take full advantage of it's potential??? I am interested. I want to know! If we can extract more power from a given amount of air/fuel by design of the combustion chamber, pistons, etc. I'm all about learning more about it!Yes, that is huge. The relationship between the piston and chamber is all you really ahve to control what goes on in the chamber, and yes, you can have a lot of control there. For instance. Quench pads, or areas. What effect do these have on combustion? What can be accomplished with a properly designed piston dome, other than adding compression?

[Hass828]

[QUOTE=Hass828;2931406]How does NOS create more pressure?
provides 02 so that more fuel can be burnt. In other words more combustion. Not attempting to argue with you, I'm in total agreement.

[MACHINEHEAD]

Steel, once we all figure out that you are the one that really knows your chit, it should be a great benefit to Foxwell Motorsports. Maybe you can sell a couple rotating assm. or even an engine. I'm going to start a thread called "Machinehead, Im the chit man". Now dont get all weird on me now. I think this is all good info and I hope that it continues. I will try to add to it if I can. However I still dont know what you are really asking. One thing just keeps leading to another. This is a huge subject. I dont think the gearheads forum is the place that you are going to get the info you seek. And it seems you already know the answers.

[steelcomp]

Steel, once we all figure out that you are the one that really knows your chit, it should be a great benefit to Foxwell Motorsports. Maybe you can sell a couple rotating assm. or even an engine. I'm going to start a thread called "Machinehead, Im the chit man". Now dont get all weird on me now. I think this is all good info and I hope that it continues. I will try to add to it if I can. However I still dont know what you are really asking. One thing just keeps leading to another. This is a huge subject. I dont think the gearheads forum is the place that you are going to get the info you seek. And it seems you already know the answers.
Well, personal attacks and sarcasm aside, this thread has gone in a few different directions, but mainly because it's a broad reaching question and I thought it might provoke some interesting conversation. Thanks for your friendly input.

[WETTE VETTE]

A flat torque curve teamed up with a light rotating assembly typically makes for a pretty snappy motor. All of the above referring to efficiency, compression and properly matched components help in achieving a flat torque curve. I doubt this answers the question, but this is my stab. Please tell us what you already know soon!!:)
Craig

[steve d]

[QUOTE=Hass828;2931406]How does NOS create more pressure?
Steel. You probably already know this about NOS, but clicking on it may enlighten a few people on the subject. Easy reading.
http://www.nr1.lt/NR1-Discovery/Charging/NOS/nos.html

[cfm]

Taking gravity, resistance to move, and etc aside, If you apply more pressure to one side of something vs the other, the high pressure side will try to move to the lower pressure side.
If you apply the same pressure to both sides of something, it will not move.
======================
More air will burn more fuel.
More air and more fuel will create more psi on the piston.
More effecient combustion chambers, ignitions, etc,etc will create more complete/uniform psi at the 'right time' on the piston. Thus, more usuable psi will be placed on the piston.
Now as far as bigger bores and larger storkes, psi = pounds per square inch, therefore, more stoke = more square inches and larger bores = more square inches. So, that is not necessarily making more combustion pressure, but mechanically multiplying the combustion pressure.
More pressure pushing down on the piston than any and all pressures that are acting against it like: crankcase psi (it's right under the piston), mechanical drag, aerodynamics, compression pressures, etc,etc,etc.
So..................I am one not understanding what you are trying to get at either, but taking your original question as I have, I say that it's all about pressure.
Yes, there are other terms to say what I have said using the term 'pressure.' Force, power, etc,etc,etc. You take your pick.
========================
Lastly, I'm not being super serious about this one. I could be talking out my azz, and probably am, but the low amt of time I have put thought into this, this is what I came up with.
Why ? As stated, I have no idea what you really mean by all of this, so I quickly took it at face value.