I was wondering because I have an 04 WR450 with the stock pipe and all the free mod's done to it. I'm in colorado there is no noise restictions here so I run the bike wide open with no baffle. I love the power and response of the bike this way, but some times it's two loud even for me and I like my bikes to run loud. I tryed the 03-04 gytr insert and was not impressed. It absolutley nutered my bike. I modifyed it by cutting it in half, still the bike felt like it had no power. Is there anyone who has tryed an fmf Q2/Q4 or the procircuit 496? I'm afraid to spend the money to find out wich one works.