Found the best cheap (free if you are lucky) pipe for my WR. Was using a Pro-circuit pipe, the bike ran great but boy was it loud. Felt a little bad making so much noise. I know it is hard to believe, but I hear some people don't like their nature hikes interupted by growling motorcycles. I ordered an FMF pipe and hi-flo header, but the muffler was on back order. Had a brain storm and started calling people who had bought YZ400's and 426s, (got a list from my neighborhood Yamaha dealer). Found a YZ426 pipe in a guys garage, got it for a six-pack of Heineken and a little shop talk. Mounts right on and runs great. A lot quiter than the pro-circuit and just as much power. Don't know how much the hi-flo header contributed, since I never tried the YZ pipe with the stock WR header.