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Originally Posted by curtis73
I guess... For instance, a head's intake port. As RPMs increase, the velocity of the air increases. There reaches a speed where (as a vague general rule) the speed of the intake charge won't go any faster and power starts to drop off. Its at this point where the power curve has peaked and starts dropping off.
Porting that same head means that you can get more CFMs before that speed is attained. Basically, you've slowed down the flow which shifts that peak speed to a higher RPM. I just remember that there is a generally accepted speed at which it peaks.
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I forget the exact measurment and how to get it, but I also remember reading an artical on it a while back. Talked about a engine builder who used to port out heads to the same size as the valve, the motors had pretty much zero bottom end power but made serious high end.
By the way incase anyone is wandering I'm calculating how much air will theoretically flow though a brake cooling duct.