I came across a gut that has a ex road race XR500 motor. Stout bottom end, Carillo rod, crank work, lotsa head work, ported, megacycle cam, shortened guides, megacycle springs, reworked and hardened rockers, 565cc, 12.5-1 compression. The motor is solid and reliable. I worked at a Yamaha dealer for a short time and see the Dirt bike and quad 450's build great power but dont last for sht. I am going to use it for flat track. Cant get an honest opinion from the FT 450 guys and there are not alot of XR500 guys in that realm. Maybe cause they get their asses whipped so there are none? I have most of the stuff to build a descent bike cheap, and will regardless, just cause I want this kind of bike. How will this motor stack up against a 450? Im sure I have them in the reliability, even w the 450 stock, but power? Any reason a single cam 4 valve cant compete or smoke a new, and IMHO a very fragile 450? Thanks for your input.