hey todd, thx for being responsible enough to spend the $ to get quieter, i wish everyone would do this. i put the big gun on my yz250f, race series w/quiet insert & s.a. the craftsmanship & fit are excellent. it is a good bit quieter than stock, & should pass an enduro sound test, but i haven't really tested it yet. i can't comment on the performance, as it is different enough from stock to need rejetting & i'm not thru with that yet.