Dick
I was there with Phall flying the plane for him while he handled the stalker radar gun. Motor was needled correctly, no sagging thru turns or uplines. The muffler simply acted like govener, the plane would go up almost as fast as it would go in a shallow dive. While the tuned pipe would be the best thing for this engine. the airframe really isn't setup for it. What would be your recomendations for a better in cowl muffler?
We know the sound you are talking about when the tuned pipe comes on and stages, it sounds like it is shifting gears. We have experienced that setting up nitro monos and outrigger hydros for the past 10 years.

take care

zonk