My thinking is that with a large cc port you need to be able to flow a large amount of air. If you engine is not pumping enough air especially at low rpm and you are running heads and a cam that are too large for the displacement the motor will not make power. If the cam, intake runner and displacement are matched well, then the motor will be able to make power across most of the rpms. My question here is what effect does compression ratio have on cam and head choice? Why does a large intake runner require more compression? Is this because with a smaller volume cylinder pressure at spark is greatly increased causing the motor to spin up quickly and pump more air at low rpm? Does that make sense to anyone?