Tim, CFM (theoretical, not actual) is easy to figure. Divide the cubic inch displacement by 2, multiply it by RPM, and divide that number by 1728. The resulting number is cubic feet per minute, assuming 100% volumetric efficiency. That number is virtually impossible to achieve on anything but a radically modified race engine, so 90% VE is a much more realistic number.
For instance: A 350 Chevy bored .030" oversize is 358 cubic inches. Half of 358 is 179. (It takes 2 turns of the engine to pump the total displacement through it.) 179 X 5000 RPM = 895,000 cubic inches per minute. There are 1728 cubic inches in a cubic foot. 895000 divided by 1728 = 518 cubic feet per minute (theoretical). 518 X .9 = 466 CFM. Now- - - - -how much too big is that 650 CFM Edelbrock 4 barrel everybody recommends?
Jerry
