O.S. 91 4-stroke, stock muffler. It now has a 15 x 4 APC, and it's running on 25% pro pattern cool power. I went down in diameter from a 16 x 4 to get faster spool up, and a little more rpms. It tached out at 9,300 with the 16 x 4 on 15% cool power 4-stroke formula. I used a buddy of mine's digi tach, so I can't wait to see what it's doing now. It is making a bit more thust, but not much.

Good to hear about the Perry. Last I checked they were in the neiborhood of $30. Very not bad...