huh - interesting stuff - where/how did you get this #? 408 CID is about 0.24 CFM per compression stroke. Wouldn't that change quite a bit depending on the pistons?
It's standard engine CFM calculation. Compression ratio doesn't change it since you can only fill each cylinder with a fixed volume of air before you compress it. The calculation is engine displacement cubic inches divided by 1728 (cubic inches per cubic foot), multiply by max rpm and then divide by 2 since it's a 4 stroke.