Most of the flying fields I fly at here in the Chicago area of the U.S. require mufflers. I have to drive about 50 miles to get to a field where I can fly with out a muffler. My unmuffled Oliver Jaguar and GB sideports turn about 5K to 6K with big props and are quiter than a sport .40 glow 2 stroke with a muffler. Jacki