cam lift

[olbiezer]

without getting into too much serious detail......can anyone tell me about cam lift and what it does for the engine? meaning my cam has 650 in and 635 ex would u use this cam to make rpm or what? thanks

[myoung]

Lift is how far away the valve moves from the valve seat to let in the air/fuel mixture to the combustion chamber. Obviously, duration would be how long it stays open.
The further it lifts and the longer it stays open, the more fuel/air goes in.

[cstraub]

Lift gives you the ability to make power at rpm, duration allows you to sustain power at rpm.

[lucky]

Lift gives you the ability to make power at rpm, duration allows you to sustain power at rpm.
The Guru !
I miss all the interesting facts about your cam class -- time to bump it :)

[Squirtin Thunder]

Chris correct me if I am wrong, on a BBF stock cast head no porting exhaust flow is 135cfm@.500lift and also 135cfm@.600lift so it does no good to lift the valve off the seat more than .500. But if you can hold that valve open at.500lift longer you will mover more air. Chris explained this to me real simple. Shake a beer can, crack the top does the presurized air move out of the can ??? And that was @.002 lift.

[SmokinLowriderSS]

Equally important to simple lift and duration numbers are the opening and closing ramp speeds and (as has been touched on) the flow potential of the port or valve opening itself. The same .600" lift, 290* duration cam ground for flat-tappets is a much milder ramped cut cam than the same specs ground for roller lifters typically.
Per a given port flow, more lift = more mixture flow, untill the port maximum is reached, then lift has no effect.
Per a given lift, even at max port flow, more duration AT THAT LIFT = more mixture flow.
Maximum lift is only reached for a very short (relative) period of time (I have no figures but I suspect under 20%) of total duration on a "normal" or "average" cam grind.
If maximum (port) flow is reached before max lift, then duration at lift above max flow greatly increases mixture flow volume. Duration below max flow helps, but to a lesser importance.
Port flow VELOCITY before reaching the valves is also highly important to cylinder filling, both in the heads and in the intake runners. High velocity starts moving quicker as the valve opens and helps ram-fill the cylinder as the intake valve closes.
Large port sizes are holding so much air it is hard to get to move toward the heads (sluggishness) and only work well at high RPM's Since the engine pulls on the runner so often the mixture tends to keep moving fwd without stopping like at lower RPM's.
To get longer durations AT HIGHER LIFTS, then steeper ramps are ground, at some point forcing use of roller-type lifters due to flat-tappets being unable to cope without scuffing & damage.
(this is purposely ignoring spring pressures to keep focus on cam dynamics in relative situations)
Very high spring pressures alter the requirement for roller-lifters due to the same forces at lower lifts & flatter ramp grinds.
The "Turbo-Jet" Chevrolet (the Mk IV) was designed to have and maintain an inlet mixture velocity of 16,000 FPM the full length of the head port passage. Sorry, my Big Block Chevy book relates no RPM to this, I wish it did. That data is from a paper written to the SAE introducing the engine in 1965.
Anyone else? Hope I have all my facts square. :smile:

[cstraub]

99.9% of the cams I have done for customers have more intake lift then exhaust which is the complete opposite of what has been mostly the norm over the years.
Yeah the beer/ soda example to me is the simplist way. The exhaust is under a tremedous amount of pressure. Once the exhaust valve is cracked the gases move quickly to the low pressure side of the valve. It is my oppinion/theory that duration here will allow the gases to escape and that lift all though a factor it is not as important as the amount of duration and the proper timing of the opening of the exhaust valve.

[SmokinLowriderSS]

I'm no cam engineer, or grinder, just a user, but I agree with your belief/opinion cstraub69.
Of course, NOTHING is without compromise and tradeoff.
I do believe inlet opening timing is most crucial with overlap moment timing being seccond.
Must get intakes open as early as possible, yet not allow too much exhaust gas to blow into the intake to dilute mixture. Must leave exhaust open as long as possible to allow exhaust to empty, but not interfere with suction on intake system. Must also open exhaust as early as possible to minimize pressure on exhaust stroke upward which fights power production through simple resistance but not vent off working gasses while still usable. This must also all work through an RPM range from 1,000 to nearly 8,000 RPM (more in some designs, 11,500 in my 'bike), a huge range to move air arround in split-secconds.

[steelcomp]

99.9% of the cams I have done for customers have more intake lift then exhaust which is the complete opposite of what has been mostly the norm over the years.
Yeah the beer/ soda example to me is the simplist way. The exhaust is under a tremedous amount of pressure. Once the exhaust valve is cracked the gases move quickly to the low pressure side of the valve. It is my oppinion/theory that duration here will allow the gases to escape and that lift all though a factor it is not as important as the amount of duration and the proper timing of the opening of the exhaust valve.
This is why I so like the Canfields. They're strength on the exhaust means less cam doing the work, and more port. Less lift is easier on springs, and lets moving parts live longer. Valve lift and the additional heat kill springs, so the more you can flow, the less lift is needed. If it's real good you don't need to open the exhaust valve before BDC on the power stroke, releasing that last bit of cylinder pressure pushing on the piston, and you can close it earlier too.

[steelcomp]

I'm no cam engineer, or grinder, just a user, but I agree with your belief/opinion cstraub69.
Of course, NOTHING is without compromise and tradeoff.
I do believe inlet opening timing is most crucial with overlap moment timing being seccond.
Must get intakes open as early as possible, yet not allow too much exhaust gas to blow into the intake to dilute mixture. Must leave exhaust open as long as possible to allow exhaust to empty, but not interfere with suction on intake system. Must also open exhaust as early as possible to minimize pressure on exhaust stroke upward which fights power production through simple resistance but not vent off working gasses while still usable. This must also all work through an RPM range from 1,000 to nearly 8,000 RPM (more in some designs, 11,500 in my 'bike), a huge range to move air arround in split-secconds.
I'm curious as to what it is you think is most crucial about intake opening.
Unfortunately, there's a lot of "lemmings" in the cyl head business, and when one starts saying something is good, the rest just kind of go along. Take for example low lift figures. Good or bad? Important or not??
What about cam timing in relation to piston speed and/or rod/crank angle (which is related to rod "n", or "ratio")
I laso hear this comment all the time: "Mid lift flow numbers are more critical than max lift numbers since the valve sees the mid lift numbers twice, and the max lift only once."
True or false?
What about flow in relation to, again, piston speed and crank angle?
How about flow in relation to lift? How much flow is best vs. how much lift?
Just scratching the surface. :D

[steve d]

You guys are bad ass!!!!!! Really great information. Now..... What about the firing swap of 3 and 2--4 and 7. Seems to be a big deal with the POLKER RUN BOYS and LSM CAMS. Hope I didn't hijack this---TOO GOOD....KEEP ER GOING.......Thanks Steve

[olbiezer]

my origenal question still remains.......is higher lift and duration going to make a engine rev higher if set up right or what?

[Squirtin Thunder]

Lift is what gets you going and duration is what rpms it.

[steelcomp]

my origenal question still remains.......is higher lift and duration going to make a engine rev higher if set up right or what?
You're asking an apples and oranges question. Yes, we have no banannas. A given displacement engine will require a certain amount of airflow to run at a certain rpm. (taking into account the many variables such as bore / stroke / rod length, and of course rules) The heads you have will allow a certain amount of airflow at a certain velocity, and ideally, should be chosen to suit your engine's needs. The cam should be designed to allow the heads to provide the airflow, hopefully at the desired velocity (velocities) to feed your engine. To arbitrarily say yes or no to your question as a generality would be erroneus. If your cam is short on lift, then yes, it's going to make more power by adding lift, but not necessarily by revving the engine higher. Typically, adding duration will extend the rpm range of an engine in the hopes of building more power, but not always the case. It's the combination of components all working together that yields the best power. High RPM isn't necessarily a good thing, if you can make the same power at a lower RPM. Power, IMO, is a misleading term anyway, especially horse power, and torque. You can build those two numbers till the cows come home, but typically, what you'r really after is the best acceleration rate between two rpm's. Getting from say, 4500 to 7000 as fast as you can, regardless of HP or Q. That's what's going to win you races. On the street, it's all about recovery from shifting, and in some cases, boats, too. Jets are a different creature all together since they basically go to one rpm, and stay there. Cam requirements are much different, BUT, if you cam for a wide power band (like my 467) you're more likely to find yourself in "good power", no matter where you are in RPM...within reason. High revving, narrow power band engines are problematic when it comes to trying to stay in that power range. They might build higher peak power, but keeping it operating in that rnage is far more difficult. They're also harder on parts, so the risk of failure is higher, which lessens the odds of winning. I know this went off topic a little, but I'm trying to relay how much thinking and planning can go into a successful engine combination, long before any money is spent. The cam is important, yes, but no more or less important than the rest of the info you need to choose the right one.

[steelcomp]

You guys are bad ass!!!!!! Really great information. Now..... What about the firing swap of 3 and 2--4 and 7. Seems to be a big deal with the POLKER RUN BOYS and LSM CAMS. Hope I didn't hijack this---TOO GOOD....KEEP ER GOING.......Thanks SteveNo hijack, it's all related. Unless you're building an all out state of the art motor, you're not going to realize the benefits from a 4-7 swap. Even then it's questionable. I think it's more one of those things that looks good on paper, and makes sense from an engineering and design viewpoint, but like a lot of other things similar, dosen't make the difference it "should". You can also charge a customer more for the "custom" stuff. Lots more.

[olbiezer]

thanks guys

[ECeptor]

BUT, if you cam for a wide power band (like my 467) you're more likely to find yourself in "good power", no matter where you are in RPM...within reason.
I'm sure you've posted it a million times aready, but can you describe your 467 (I assume it's a 0.060 over 454)?
- heads
- cam
- intake
- carb
- compression

[steve d]

No hijack, it's all related. Unless you're building an all out state of the art motor, you're not going to realize the benefits from a 4-7 swap. Even then it's questionable. I think it's more one of those things that looks good on paper, and makes sense from an engineering and design viewpoint, but like a lot of other things similar, dosen't make the difference it "should". You can also charge a customer more for the "custom" stuff. Lots more.
GOT IT STEEL-----THANKS....Steve

[Carnivalride]

I'm sure you've posted it a million times aready, but can you describe your 467 (I assume it's a 0.060 over 454)?
- heads
- cam
- intake
- carb
- compression
Common Ed keep up now! :rolleyes: :rolleyes:
Just because I like ya I did the leg work for ya. :D
steelcomp build (http://www2.***boat.com/forums/showthread.php?t=88308) steelcomp dyno (http://www2.***boat.com/forums/showthread.php?t=93008)

[HP350SC]

I'm curious as to what it is you think is most crucial about intake opening.
Unfortunately, there's a lot of "lemmings" in the cyl head business, and when one starts saying something is good, the rest just kind of go along. Take for example low lift figures. Good or bad? Important or not??
What about cam timing in relation to piston speed and/or rod/crank angle (which is related to rod "n", or "ratio")
I laso hear this comment all the time: "Mid lift flow numbers are more critical than max lift numbers since the valve sees the mid lift numbers twice, and the max lift only once."
True or false?
What about flow in relation to, again, piston speed and crank angle?
How about flow in relation to lift? How much flow is best vs. how much lift?
Just scratching the surface. :D
I'm going to take a stab at some of this. I believe the most crucial factor in intake valve opening is the engine rpm, or desired max rpm. At low rpm, the intake can open late for a smooth idle. At midrange speeds it needs to open sooner to flatten the torque band. At higher rpm it would ideally be retarded again for peak power.
I would think low and mid lift flow figures would be a better indication of how a head flows than max lift figures. Regarding the statement "Mid lift flow numbers are more critical than max lift numbers since the valve sees the mid lift numbers twice, and the max lift only once." really makes no sense to me, because the valve "sees" specific lift in degrees of crankshaft revolution. It is probably at max. lift longer than both .400 events.

[ECeptor]

Common Ed keep up now! :rolleyes: :rolleyes:
Just because I like ya I did the leg work for ya. :D
steelcomp build (http://www2.***boat.com/forums/showthread.php?t=88308) steelcomp dyno (http://www2.***boat.com/forums/showthread.php?t=93008)
Thanks man. After reading about it, that engine would be much better in your boat rather than mine.

[Daytona100]

What if you add 5lbs of boost to the picture? Iv heard you can run a bigger cam and head if your supercharged. :coffeycup

[SmokinLowriderSS]

I'm curious as to what it is you think is most crucial about intake opening.
Unfortunately, there's a lot of "lemmings" in the cyl head business, and when one starts saying something is good, the rest just kind of go along. Take for example low lift figures. Good or bad? Important or not??
What about cam timing in relation to piston speed and/or rod/crank angle (which is related to rod "n", or "ratio")
I laso hear this comment all the time: "Mid lift flow numbers are more critical than max lift numbers since the valve sees the mid lift numbers twice, and the max lift only once."
True or false?
What about flow in relation to, again, piston speed and crank angle?
How about flow in relation to lift? How much flow is best vs. how much lift?
Just scratching the surface. :D
OK, been a long week and been to tired to think on this one Steelcomp, wasn't ducking it tho. :D
My opinion of intake opening point being most important is because it is the initial point that governs cylinder filling. It's timing has to be an efficient match for the port runner volume so as to be able to get mixture flowing as soon as posssible, as fast as possible (port flow velocity). Too early and leftover waste gasses not only dilute the mixture, but push it backwards up the manifold. Too late, and the piston gets too far ahead of the mixture and cannot pull much of it into the cylinder.
I only believe it to be of greater importance than overlap by a small margin (which I deem #2 in importance) since much the same effects are present durring the overlap timing. Trying to get the last vestiges of exhaust out without either diluting or exhausting an excessive ammount of intake mixture.
I have no idea even how to start to relate cam timing to piston speed/rodangle/crank angle, so I'm not gonna try. A man's got to know his limitations.
I laso hear this comment all the time: "Mid lift flow numbers are more critical than max lift numbers since the valve sees the mid lift numbers twice, and the max lift only once."
True or false?
I feel true, TO AN EXTENT, and also an over-simplification. The valves have no concern over the numbers, nor the engine. I do consider flow to be more important than maximum lift, for several reasons.
Any lift, above that which generates maximum port flow, is wasted. Now, not quite totally wasted, as the higher you lift the valve, the longer the port stays at maximum capability (assuming the engine can use it), but there is a point of rapidly diminishing returns. Consider a .650" lift cam (or higher) in a set of BBC small oval port "truck" heads. Will a .700" lift cam help make any more power, not likely, will a .500" lift cam work just about as well, probably. Put that cam in a 502 with ported large ovals, and the lift is no longer "wasted".
The same effect, to a very great extent, could likely be reached at lower lifts by the opening ramp cut, to get the valve to lift sooner, and faster, and to stay at a lower max lift, yet achive the same maximum flow capability TIME as the higher lift cam. What if max lift is restricting flow by being too small, then it becomes more important, at the time. What if max lift is restricting the flow by being too big for an aplication, such as Rectangle port heads, a really tall roller cam, oversized valves, on a 396 in someone's Chevelle SS driving arround town. Now, yes, there are a host of problems in THAT scenario other than a motor that cannot use all the lift it sees, but the cam isn't helping cover for too much intake area.
Now, all of this is situation-specific, I won't very often make big specific "catch-all" claims (other than the one I just made about specificity). Each part combination is different. What works in 1 may, or may not, work in another, and will NOT likely work in all.
I think I keep trying to speak of it in a "flow related to lift", because it is, and has to be.
There was a time when I would have thought "bigger is always better", but I have seen, tested, done a little, thought a lot, talked, listened, and managed to come to the comclusion that "it has to fit" instead of "That'll be great, it's bigger".
I do learn a lot of stuff on here from the experienced tho, so I am staying awake here, and paying attention, seeking advice from time to time as well.
Heck, first performance motor I built in a looooong time is the 454 in Lowrider. OK, it's not an 800+HP blown, "performance" motor, but my boat SHOULD NOT be going 90+mph, and I am not going to try (I know people who have done it in a Taylor and do not reccomend it). She started out at about 280 HP stock, I sought advice from DuaneHTP, I feel the guidance was good, She is a solid 350 HP and easy to drive, but with more available. Exhaust improvements this winter should net me 400HP for no loss in driveability. I spoke to a local shop that Duane also uses, and they will port my heads next winter, just a stage 1 job and larger valves, should put me very close to 500HP. I have no need for stage 2 or 3 work (diminishing returns on increasing $$$$) My torque curve just keeps growing taller and flatter/fatter as well, so my setup sure seems to "fit" well.

[SmokinLowriderSS]

Oh, by the way steelcomp, just read thru the threads on your engine build & dyno. VERY nicely done. :smile:

[cstraub]

What if you add 5lbs of boost to the picture? Iv heard you can run a bigger cam and head if your supercharged. :coffeycup
The word Moderation fits alot of things in life including engines. If you go blown with a compressor that is well matched to the CID and desired rpm then the cam will be realtively small for a broad power band. Reasoning is the blower will do the work so a large cam does not have to be used to "coach" air and fuel in. Where you would need a large cam is with a mismatched combo or an application that requires a narrow power band.

[cstraub]

I take the stand that all the valve events are critical. Proper valve event timing in relation to crankshaft degrees allows an engine to run "in sync".
I tend to look at this way:
Exhaust Closing: Needs to evact the gasses and assist with "pulling the intake charge in during intake opening...
Intake Opening: Needs to open at the correct point of BTDC to "get the party started"
Intake Closing: Needs to close after all available air has been collected, is very critical with large stroke engines where the RAM effect is much more prevelant.
Exhaust Closing: Needs to "pop the top" exactly at the right time to relieve pressure so that the engine is not working against exhaust pressure and loosing presious HP due to parasitical losses.
Just my .02$

[SmokinLowriderSS]

Agreed Chris.

[Unchained]

A piece of trivia,
A friends dad used to race dirt track cars back in the 1940's and 1950's.
He said that to get more power out of their flathead engines they would take the cam to the bench grinder and BY HAND grind down the back side of the lobes. Now is that a lost art or what ?