So, what is it that makes an engine accelerate?

[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!

[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

[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 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

[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.
Tommy