I need some muffler help. I am planning to use an OS .91FX, inverted, to pull this plane around the sky. Unfortunately, I can't seem to find a pitts-style muffler for the .91. A call to product support at Top Flite yielded the following suggestion: use their in-cowl system, but it needs to be "opened up" or the engine will overheat.

I have two questions: 1. Does anyone out there know of an incowl system that will work wothout modification, and 2. Does anyone have experience modifyingthe Top Flite muffler for use on an OS .91FX?