I have a 450 with 27's and I just installed a DynoJet kit and K&N. It gave noticeable power gains. I have way better throttle response, about 12kph gain in speed, and better low end power. I have been very happy so far. Ive ordered a HMF untility as well and expect more gains. Go to the HMF engineering web site. They have a forum and you can talk to their engineers and ask all the questions you want. If I knew how to post the link i would.