I'm not sure why anyone would want standard port heads on anything larger than a 383 unless they were building a low rpm street car. McFarland's eqn doesn't hold up to reality.
The formula is a starting point for comparisons, but works better when using a higher velocity like .55 Mach vs .5 Mach. At high altitudes, like here in Colorado, port cross section / velocity seems to affect performance, maybe more than at low altitude?
