Ken, to be honest it's purely a personal preference, not scientific. To me 2 strokes engines are whiney, raspy noise makers. A majestic plane like the Skybolt deserves the low rumble of a 4 stroke. I have 9 planes, 8 have 4 strokes the ninth will be my first gasser ( yea I know it's a 2 stroke gas motor). In my Skybolt the motor is mounted inverted so the stock muffler works fine. Minnflyer (Mr. Skybolt) will second my opinion of 4 strokes motors.