Originally Posted by chip-3door

It all comes down to the fact that no matter what you do with fancy cams and intake lengths and all the rest of it, you will fundamentally never get significantly past a certain amount of air into an engine when there is no boost involved.

Even if you hold the piston at the bottom for a week to give it plenty of time to fill up a 500cc chamber is only going to hold 500cc of air, which in turn limits the amount of petrol that can be burnt at the optimum AFR (around 12.5)

Its actually fairly obvious if you stop and think about it in terms of the volume of air that an engine can consume.