Mac's got a pre-tuned pipe that is made for the OS.46 sf or fx. This pipe works just as good for the TT too. I know.. I use one on both of my engines, OS & TT. I gained 1100-1200 rpm on both. There much quieter than the stock muffler too. And the SOUND!! When it "comes on the pipe"... ;-0 yea!
Suptter