ORIGINAL: jetmech05
well i take a clear piece of plastic pick up the cowl mounting holes trace out the engine head cut it out in the clear plastic. install the cowl with the plastic over it trace out the hole on the cowl and cut. i use a dremell with a cutting wheel for straight lines and sanding wheel for the corners.
make sure that you have enough space around the engine head or exhaust to allow airflow, or you will over heat the engine.
thats how a full scale cools and heats recip engines, with cowl flaps that close or open the back of the cowl for airflow around the cylinder heads
What I have done is similar, I use paper templates mark the Engine cut outs. I then trace them onto the cowl. I then drill around the inside of the markings, pop the plastic out and clean it up with the dremel.