Two different types of planes, apples and oranges but you can see how it was done, I added some white paper so you can see the cooling air flow. Extra 300, bottomg of the cowl has been cut a lot. Pattern plane, the fuse was designed for a tuned pipe and the air flow goes right on through the cowl and out through the groove. Like Joe mentioned, you must get the inflow out of there taking the heat with it. 1-3 is about normal for good cooling. I have a friend that hates to cut up his cowls so he opens just a little then opens more as he flys his plane until it quits over heating. Try your plane/engine without a cowl and make sure cooling is the problem before you start cutting. It may just be a tune problem?