Question for you experienced guys: how much air has to go through the cowling to cool the engine?

I've heard that the size of the intake/outtake is NOT that important. What IS important is the RATIO between the two: if intake = 1, outtake must = 3.

Is that correct? Anyone else have ideas on how to do that so the engine doesn't over-heat. 2 or 4 stroke makes no difference I hear.

Jack