Both a standard side dump and wrap around Pitts mufflers are little more than exhaust deflectors with a spark arrestor. There's nothing inside them to help anything. Want to put that to the test? Tach the engine with and without a muffler. Spend a few bucks and to that test with mufflers from a few different manufacturers. Get back to us with the revelation.

Can you improve on them? Sometimes, but the outlet pipe length isn't going to make a difference. Diameters might, but not much. Punching out the spark arrestor usually helps a little. None of this applies to the old B&B mufflers. Those always reduced performance.