Great thread with lots of good information. I have been lurking on this site for a long time. Just picked up my new 07 WR450 yesterday. Took it for a putt around the neighborhood and I am a bit disappointed. I knew it would be down on power after reseaching on this site but, I didn't expect it to be that bad. My YZ400F was WAY faster than this. The WR is sweet other than the stock tuning.
Anyway a pipe is going to be my first purchase (along with the other mods listed on this site). The bike is LEAN out of the box so, the person that posted that, is 100% correct. It is so lean I won't ride it again until I get it dialed in. The pipe was glowing red and it actually ran better with the choke partially on (both signs of a lean condition). You can feel the bikes power is choked up bad. It is also true that a more free flowing exhaust will require a jetting change (richer).
I planned on buying a slip-on originally but, it looks like the Dr D full system is the was to go. Does the fact there is no heat shield cause any problems for any of you? (burned boots/pants, etc...) Not a big deal I can weld stand-offs and install heat shields if needed.
Just to make sure, you do know there is a throttle stop that only allows for a half throttle. This would explain the lack of power. Again, just checking.