I just got my new CHM P-R4 exhaust system for my 04' yzf450 yesterday. It is a spark-arrested, stainless steel system. I installed it last night, and went for a good ride today. I have to say that I am very pleased with this system. Fit/finish is quite good, it seems very sturdy, and installation was a snap. The bike seems slightly quieter than stock, but with a much deeper, pleasant sounding exhaust note. Once on the trail, I noticed that the bike seemed to pull better from much lower in the rpm's, with a very smooth transition to mid-upper rpm. I found that this made it much easier to ride in tight, hilly sections. Mid rpm seemed slightly beefier than stock, with no noticeable change in the upper rpm. The only point of any concern, is the bend on the headpipe. It has a wider radius bend than stock, which causes it to stick out a little farther, much like that of a kx450f. But, all in all, for $239 US for a complete system, I am a happy camper.