I'm not sure that I agree with the notion that the stock muffler is the "best" at "effective exhausting" for this motor.

Bisson makes a wrap around pitts, but you asked for a side dump.

Slimline doesn't even list a muffler.

So maybe the stock muffler is the "only" muffler available right now. But does that really make it the "best"? [sm=spinnyeyes.gif]

Side dumps aren't really going to do much for performance anyway. They are just a diverter to keep the exhaust off the plane. If you want performance out of a side dump, it would have to be pretty darn big and have some mighty special baffles inside.