big dave

I've had the ported heads on my car for around 5 years and am wondering now how good they really are. We were having a discussion recently on the affect a cam with similar duration, but more lift, would have on power, if the heads were a restriction.

I thought that with a good set of heads, much higher gains would be seen with more lift because of the increased demand of the good heads.

The opposing view was the complete opposite. He said that with a poor set of heads, more lift would produce much higher gains because of the lack of head flow and the greater demand from the motor.

Using my car as the test subject, when I had my original heads/cam package, the cam was spec'ed at 222/230 .533/.544. After my motor grenaded it destroyed the original cam. A friend had a gm846 cam with the same exact duration but with more lift .544/.563. With this cam my car picked up 18 rwhp even through a larger stall converter.

Knowing this, can we now assume that the heads are the choke point or not. Thanks for your opinions.

SStrokerAce

What was the LSA on that other cam? Were they both installed at the same ICL?

FWIW the lift will matter if the motor needs it, reguardless of the heads. Especially on a cam that is smaller than what would make the most peak HP.

More on that later.

Bret

big dave

They were both cut on a 112 lsa and installed straight up.

big dave

Thanks for the reply Bret.
If the head doesn't have the flow capability, wouldn't it become a bottleneck, reducing the amount of power gained regardless of cam lift. The main reason I'm so intereste in this is because we're working with similar cams (duration wise) with a pretty small increase in lift, yet it yielded what I consider to be a substantial gain.

SStrokerAce

Well there is a concept in engine design cam design called curtain area. Valve Size and Valve Lift basically. Most motors are limited by this in pushrod 2 valve land. Now when you are below the point where the motor wants more curatin area and you add more valve size or lift then you will pick up HP reguardless. The heads can have something to do with this as well. A better head in terms of flow quality and how well if feeds the cylinder will gain just like a head that's not as good, in fact it could gain more. This is not due to just flow numbers either. I know your thinking that a head that flows 255 @ .500, 260 @ .550 and 260 @ .600 will not gain as much as something that gains more as you open the valve like 255 @ .500, 270 @ .550 and 280 @ .600. Both of those motors are going to gain power due to increased cylinder filling from the increased curatin area.

I'm also guessing that your finding more HP at higher RPM as well with the higher lift cams.

BTW different cam lobes can also have a lot to do with the increased HP numbers not just the lift. Lift is a part of it but you almost can't get this gain without another trade off.

Bret

big dave

Bret, big thanks for shedding some light on this subject. You really do know your stuff.

SStrokerAce

Wish I knew more....