I have the k&n filter, and the Spyker mod.......the only two things I have done are......a/f adjustment, and I put a piece of plastic behind the screen from the Spyker mod to lessen the air flow......Spyker gave me something to use, but you could use the plastic from a pack of blank cd's........I have not rejetted nor have I done the Scar mod.......my bike performs just fine.....