What id like to know is there a difference in valve sizes between the crf and the trx? I know Duncan Racing sells a big valve set up for the trx however i feel like someone at sometime mentioned that the crf actually already has these bigger valves in it? If that is the case then id go buy a new crf head from service honda for the crf for 200.00 and get the valves for it, say another 100.00, and send it out to get ported and have no down time. Is this all wrong or what? Thanks in advance to anyone that reply's. By the way, this 450 kicks ass, honda should have made this thing 10 years ago when we were cornered into buying 300ex's!