Using the bore size, the piston speed in fps at every degree through the 180 degree intake stroke, the average area of the intake port (determined by port length and cc volume) and of course the peak rpm of the engine to calculate the average air velocity through the port. The maximum air speed that can be utilized is determined by the intake port design. The higher the velocity up to the maximum the head can handle the better. If the port area is too large for a given engine/rpm range then the engine can't create enough pressure differential to get the air speed up where it needs to be to make good power. Intake ports are designed and/or matched to an engine combination based on air speed not cfm.