Quote: At what point does good swirl/tumble/mix become more important than just velocity? If we're talking a couple % faster in a 44-year old head vs. a 24-year old head, I choose the newer one every time.
Clair
Absolute Velocity(cfm) is a very small factor when attempting to judge combustion efficiency.
I did some cylinder head development with Cummins in college and they actually measure "SWIRL TORQUE" in the cylinder to judge comb eff. This quantifies exactly how fast the air is swirling around once in the cylinder. An increase "swirl torque" had a significant impact on comb eff, but was somewhat independent of absolute port velocity ei: more HP, more mass air flow and less HC emissions from the same CFM.
In the last 20years steady state CFM has become an increasingly less significant design aspect of new OEM cylinder heads.
Bottom line: When in doubt always go with the newer designed head.
