I just put on a YZ exhaust onto my WR450, wow, the thing is now an animal. I have not hit the trails with it yet, I just rode it in the field next to my house for a bit. It is a big improvement over my PMB insert with the first baffle removed. It is loud, though. I am planning on ordering a Dr D spark arrester which will probably knock it down a decible or two and will use my stock exhaustfor competetions, when the noise restrictions are 96db. There were probable a few pounds of weight savings and the thing was only $70 on Ebay. They are tough, too. I would recommend looking at this option, as it is an effective, inexpensive mod.