[GT40FIED]

There are programs for that. I'm sure you'd have to take into account intake port size, approximate CFM, velocity, volumetric efficiency, fuel intake, runner size and cross section, valve size, rocker arm ratio, compression, timing specs, desired powerband, redline, and displacement among other things. Then factor in the effect that a given cam (whether it's hydraulic, hyd. roller, or solid roller can make a difference too) will have on these issues. For instance, a cam with a bigger lift and more duartion without a change in intake runner size and cross section (or CFM) won't give you much of a boost. A dual pattern cam (usually with more duration on the exhaust side) will evacuate the cylinder better and increase the velocity of incoming air since, while the exhaust valve stays open for a short period of time while the intake valve is opening, it will create a pressure difference which sucks air in quicker. Change the brake specific fuel consumption or swap the intake and you've got a different set of numbers. It's fairly easy to give a generalization for a given engine and the desired results, but it's a lot harder to predict actual power numbers without a specific formula or program to do it for you.