"By increasing the ENTRY hole to a larger dimension than the EXIT hole it is now a form of baffle where the increased CFM now takes longer to escape and is forced to circulate inside the cowl."




I agree. However, this is undesireable in our planes. The longer the air stays inside the cowl, the hotter it will get. The exit hole should be at least 3 times the size of the entrance hole. This will ensure that the air does NOT dam up and circulate inside the cowl.