My buddy and I both have 2005 YZ 4-fiddy's and have been checking out some mod options. Our local dealer was nice enough to let us test the Dr. D exhaust system and told us if we didn't like it that he would put it on his own bike. He was sure we would be more than impressed. Make note that our stock bikes have always been dead even. We installed the pipe on my bike and headed for the sand dunes. We drag raced several times and stayed dead even. No difference. We then went to choke cherry hill for some climbing. On the first run his stocker out climbed me (me on both bikes). He is running an M5B and I had a Pirrelli MT32. We drag raced up the hill and stayed pretty even other than he went higher on his stocker. We went back to the truck and traded back rims/tires to see if the tires were making the difference. Same results. The Dr. D did not make any difference. None! I'm not here to bash any one brand, but I'm sure glad that I didn't spend 500 bones on this thing. Does anyone know if the pipe changed from 04 to 05? Maybe we had the 04 version??? What really works out there? I have read several threads of people liking this pipe, but has anyone really done a test like this? I honestly felt like my bike was a little crisper before we started racing/climbing. Does the different sound just make it seem that way? I'm confused.