How big does the hole need to be? Right now, I have a hole for the prop that is about 1 1/2 inches in diameter. The exit hole on the botom is 3" by 3". If the 1 part intake for three parts exhaust holds true, then I am about right as it sits. The hole is blocked somewhat by the prop and spinner and you can see about 1/4 inch all the way around if you look straight on at it. Here is a picture of my idea of cutting to the left. The black area is what I was thinking about cutting out. Thanks for your help on this. It looks like I should have left the front alone, and opened up the bottom more. Oh well, I will come up with something cool to do with the cowl to hide the fiberglass.