I put a SX silencer on my '00 400 exc, it woke up the power a bit, revved quicker and was alot louder, I'll run it when riding MX, but for trails I like the stealthness of the EXC pipe, the FMF Q series looks like the Euro technology KTM uses on its EXC's over the pond. By the by, a friend put the EXC pipe from my 400 on his 520 SX, claimed it made the midrange much more potent, cut top a little, I found that the 520 became much more manageable, this big low end rush smoothed out, but it still has monster torque. I was thinking about a 520 for a bit and decided to stick with the 400 for another season. Although putting a 520 P/C on the 400 is still a curiousity question for me.
another .02:cool: