Yep, The same muffler that they shipped with the .40, 46, and .52 also. I think it is just to small and retrictive. I was also running 20% with a 10-8. It might be ok with a 11-7, like the manual recommends and states that it turns that at 13,500. From my experiences with the engine now, I would either run a Jett, Tuned Pipe, or a Tower .46 muffler minimum. I ran the stock muffler to get some numbers for you guys, but also to show my buddy how much of a difference the Jett muffler was going to make. It might work with an 11-7, but I was running an 10-8. To some guys it may be fine, but to me, I thought it really sucked. I am also compairing it to the Jett muffler though.

I think the muffler was an after thought, as in "It comes with a muffler".[X(] I think most people who run this engine will be running tuned exhaust systems anyhow. The engine is marketed to utilize them in both there advertising and in the manual. I wish they would just market the engine without the muffler, since it wasn't worth the time to install it.