Camshaft lift question

[metriccar]

Let's say you have a restricted (basically stock) engine and exhaust manifolds.

Assuming all else is equal, duration at .050, LSA, etc, but one has a .50" lift and the other has a .54" lift, what is that going to do to : low RPM power, midrange , and top end?

[T-flow]

I don't think much will be seen. But depends on the engine were talking about? Also cam timing events will have more effect than lift.


T-flow

[Joel Dubose]

It depends on to many factors than to just focus on lift. Typically you will gain some lower rpm power, not much if any up top. This is just a general statement but it's pretty close.

[CamKing]

It depends on to many factors than to just focus on lift. Typically you will gain some lower rpm power, not much if any up top. This is just a general statement but it's pretty close.

It'll do the exact opposite of this.

It won't really help the low-end power, because at lower RPM's the added lift isn't needed.
As the RPM goes up, and the CFM requirements go up, the added lift will start helping the power.
You won't really see the peak HP RPM go up, but it will hold on a little longer.

[Joel Dubose]

Creaaing the lift

It depends on to many factors than to just focus on lift. Typically you will gain some lower rpm power, not much if any up top. This is just a general statement but it's pretty close.

It'll do the exact opposite of this.

It won't really help the low-end power, because at lower RPM's the added lift isn't needed.
As the RPM goes up, and the CFM requirements go up, the added lift will start helping the power.
You won't really see the peak HP RPM go up, but it will hold on a little longer.

Well I haven't seen it work out this way. I've added longer rockers to a multitude of engines on the dyno. In theory more flow was why I increased the lift through rocker ratio. Generally speaking and I say generally because there are way to many factors involved to be making a blanket statement. I gained low end power. As the RPM's increased so did the amount of air out the exh. Call it gulp factor if you would like. It didn't make sense because the airflow gains were at high lift, no where near overlap. None the less the bottom line was increasing the lift also increased valve speed showing an increase in flow. It's just a matter of what the engine does with it as to what it does for power. A running engine does things that on the surface doesn't make sense. Over time I've learned to see the results, not just in power or trq. but in results from all the other numbers on the dyno sheet. Example , bsac, Ve, airflow through the engine etc. For the record I'm working mainly on race engines. Not so much on stock engines with a cam.

[CamKing]

We're not talking about changing rocker ratios.
Changing rocker ratios also changes effective duration, if you don't change the lash with the rocker ratio. It also changes the overlap area.

When keeping the duration the same, and increasing lift, you increase the top-end power, and it holds the power a little longer.

[metriccar]

I talked to a cam grinder for about an hour and his rule of thumb was more lift equals more low end power, all else being equal, which if someone asked me, I would have thought the opposite. But if anything I could see it improving the whole RPM range (more air in at all RPM's but no more duration/overlap=more power). In trying for more low end power from what I have now (COMP 12-646-5) I was trying for a shorter duration exhaust vs. intake to prevent reversion on stock exhaust manifolds (some people say you want more duration on stock exhaust manifolds to help with the weak exhaust but if it's weak my opinion is that it would just go up into the intake if it's easier to go there than istead of exhaust so you'd be better off with shorter duration exhaut, whereas my cam has longer duration, but from what I am being told, shorter exhaust duration for my type of motor is more helpful for higher RPMs and lower RPMs, you don't see much difference).

[novadude]

some people say you want more duration on stock exhaust manifolds to help with the weak exhaust but if it's weak my opinion is that it would just go up into the intake if it's easier to go there than istead of exhaust so you'd be better off with shorter duration exhaut

Wouldn't that depend more on WHERE the Exhaust centerline is located? I would think there can be a real big difference between too cams with the same exh duration/ Let's say one cam had an early EVO, while the other put all of the extra duration on the closing side.

I'm not sure you can generalize.

[SchmidtMotorWorks]

I talked to a cam grinder for about an hour and his rule of thumb was more lift equals more low end power, all else being equal, which if someone asked me, I would have thought the opposite.

Talk to a different cam grinder.

[metriccar]

some people say you want more duration on stock exhaust manifolds to help with the weak exhaust but if it's weak my opinion is that it would just go up into the intake if it's easier to go there than istead of exhaust so you'd be better off with shorter duration exhaut

Wouldn't that depend more on WHERE the Exhaust centerline is located? I would think there can be a real big difference between too cams with the same exh duration/ Let's say one cam had an early EVO, while the other put all of the extra duration on the closing side.

I'm not sure you can generalize.

Yes. I've been looking at the 12-647-5. Which has a later evo, shorter exh duration but higher lift than the 12-646-5 I'm running now but is billed as a cam for headers. Intake lobe looks the same. I'm thinking comp has it reversed for which would be good for headers and which would be good for manifolds but how would I know more about cams than comp

[CamKing]

I talked to a cam grinder for about an hour and his rule of thumb was more lift equals more low end power, all else being equal, which if someone asked me, I would have thought the opposite.

Talk to a different cam grinder.

Or ask him to put his dad on the phone, and go back to mopping the shop.

[BigBro74]

some people say you want more duration on stock exhaust manifolds to help with the weak exhaust but if it's weak my opinion is that it would just go up into the intake if it's easier to go there than istead of exhaust so you'd be better off with shorter duration exhaut

Wouldn't that depend more on WHERE the Exhaust centerline is located? I would think there can be a real big difference between too cams with the same exh duration/ Let's say one cam had an early EVO, while the other put all of the extra duration on the closing side.

I'm not sure you can generalize.

Yes. I've been looking at the 12-647-5. Which has a later evo, shorter exh duration but higher lift than the 12-646-5 I'm running now but is billed as a cam for headers. Intake lobe looks the same. I'm thinking comp has it reversed for which would be good for headers and which would be good for manifolds but how would I know more about cams than comp

IMO
you are talking to a wal-mart customer service rep there buddy, not a cam grinder