I put a Random Tech downpipe on a few years ago (I think I was actually their second customer). I didn't do a before-and-after dyno, but it was the only change I made at the time. I already had an aftermarket exhaust, and I think it did make an improvement in performance. It was nothing a significant as changing out the stock exhaust or putting on a boost controller, but it did help across the rev range. Probably the best part though, was that it really helped out the sound. I was kinda surprised, but it really made it more throaty than with the stock cats. Also, I've had absolutely no problems with emissions. We have both visual and output checks where I live, and it burns as clean with the RT as it did with stock. They ain't cheap, but I'm glad I did it.