I tried tried it for fun. I made an aluminum adapter. I got one of these:

http://www.acehardware.com/product/i...Id=41022564614

It looks like it will fit into what I am doing pretty well. The engine turns 6800 with a 20 x 10. That is about the same as what is did wiht the factory muffler minus the guts and a biggger exhaust opening. I guess I'll have to try it without a muffler and compare. With my adaper I can also use a straight pipe, or anything else 3/4" pipe thread.