if it helps any for a reference, here is my Fox .45 wart engine running as a diesel. I was using DDD fuel and a Master Airscrew 12x8 prop on it and I got about 9,400 RPMs. That should improve over time as the engine is new and still being run in of course. I figured the old timey dinky Fox muffler is fine on a diesel engine due to its unique combustion processes.

[youtube]http://www.youtube.com/watch?v=WTp3Lkr9pSw[/youtube]