Sometimes we take air for granted because it is the environment we live in, and we forget that it has mass, density, and inertia when moving. David Visard has a way he calculates port energy (I think that is what it is called?) which I think is flow and velocity combined. I still don't understand how McFarland uses 1/2 Mach speed (around 563 feet per second) to estimate peak torque RPM?
