Factory heads max out on flow somewhere around 0.400" lift and at 28" depression they flow between 220 and 228 cfm. On a V8 engine max horsepower is roughly 2 hp per cfm of port flow so you see the 440Source heads can support about 75 more horsepower than an unported stock set. Plus they (as well as most aftermarket heads) have a better combustion chamber than the OEM open chamber heads.

R.