In my area we had a class of pylon racing that allowed up to a .46 two stroke with any aftermarket muffler. Most guys ran with a OS .46 FX or AX and ran the Jett or Nelson type tuned mufflers. With a 9.5x7 most were in the 16,000 to 16,500 range on 15% nitro. I would call that pretty respectable. However most engines did not last an entire season. Myself I went the expensive route and ran a Rossi .45 with a Nelson tuned muffler. With an APC 9x7.5 I would usually get around 17,200.