I am putting together an ARF that has a cowl and I am hanging a .91FS on it. This is the first model I have where I have to deal with a cowl. While I have learned a little about 4-strokes, I know even less about 4-strokes inside cowls. So I have come to the experts here on RCU for some instructions.

The engine is mounted 90* from vertical and I have a pretty decent sized opening for the heads and access to the glow plug. With this configuration, the muffler is to exit the cowl thru the bottom. I guess the first/main thing I need to know is how big the opening for the muffler should be and why? Do I cut it just big enough to fit the muffler or do I need it bigger to allow for plenty of air movement to help keep the engine cool. Do I just maybe want to cut a long oval type opening so that the cowl will slide on past the muffler and give it even more "air"?

I appreciate any and all help with this as I really don't want to run the risk of burning up a new 4-stroke engine.

Thanks,