I had a 480 yfz with head porting, valves, springs, CP piston, bigger cylinders, etc. It was still pretty much a turd. My g/f rode it and said she liked it because it didn't run like the banshees. lol! It dropped a valve and blew the whole top end to hell. Cost me over $1k to fix it and 2 months later it blew a head gasket. I traded it to a kid for a 4mil banshee, and he even knew it had the blown gasket! I got the better end of that trade!
-Jared