Well, I put my new Dr. D Exhaust on my 07 WR450, had to raise the needle one notch (I have the GYTR kit). Got a nice tan color on the plug, runs great. Now, I was going to do an oil change after my Sunday race and discovered the Dr. D header pipe blocks the upper right oil filter bolt. So in order to change the filter you have to remove the entire exhaust system. They only needed to move it up a 1/4 and it would have cleared. I emailed Dr. D to inform them of the bad engineering.