What is your HP to cube ratio?

I think there is a formula that has to do with the headflow that is superior to the HP/CID rule. Try this calculator, although it doesnt take compression into effect. http://www.wallaceracing.com/calcafhp.php
For instance, I put 28 inches of water , 220CFM @5000 for a "562" (J and X similar) and 403 for my CID and got 417@5533rpm.