After getting some great advice from this board (Thanks to The Blue One in particular), I installed a Pro Circuit 496 (96 dB CA legal pipe) on my WR450 last week. I rode about 60 miles in the desert today and am glad to report that the performance was awesome - very comparable power to the stock pipe without the plug. The pipe is expensive and I had a few hassles with installing the it - no install instructions provided and no mounting hardware provided (YZ upper rubber grommet, collar and a longer bolt are needed) and bad info from PC on jetting. PC recommended a 162/40 combo and it ran like crap. The local dealer was able to dial it in with a 162/45 - which was the ticket! The pipe is solid, looks great and fits very nicely. I am a happy and noise level compliant rider!