Dubach-period! It's good enough for Pro-Circuit and others to copy. And Doug rides the track vs. the "Dyno-chart" crowd (Dyno charts don't win races/Good acceleration and traction do). How many other people or companies have the "Data-base" that Doug does? Ask anyone who's running one. If you do get a pipe, be sure to ask a lot of people at your local track. A lot of pipes for the YZ/WR don't do much of anything. The only real tuning advantages seem to come from pipes w/ stepped headers (I consider the header to be the entire pipe all the way to the muffler). If you measure some of the real popular pipes out there you'll find that they're not much different than stock. Take your time and ask people like Doug, Ty, Mike Young-etc. I'm pretty sure you'll get some honest answers. Look at the 2 replies before this and you'll find a couple of guys that are real happy with their systems (I don't know about that brand/seems to me "megaphone" systems are REAL loud and produce -usually- a lot of topend). Good Luck.