as stated in one of my earlier posts, Carb, exhaust, clutch, weight, tires, rpm, gear ratio, and i will add roller cams, can all be easily checked. If you build a 420 ci engine and run it with a 500cfm 2 bbl and 13/4" exhaust tips, this will severely kill the 420. The engine is an air pump, no air in and no air out = no power.