i build F500 motors for oval track racers here in the north east. you can go .020 over bore. have to run a pipe made for these, a few different places have them. stock stator, timing ,etc. only SP1 piston's are allowed. or o.e.m. if you can find them. no wiseco, etc. no cylinder shim's head cut etc. these are heavily teched at races. that said this is one of if not the best motor Polaris had. 72 h.p. out of the box 7800-8000 rpm. we have 100+ h.p. 500 based motors that have been bullet proof. you have to know what your doing. most didn't. even SLP that mod was junk. what is truly amazing is the speed these go on the oval. at one race here in N.H. they ran F5 against 440 champ sleds . F5 in the first row champ sleds in the second row. 5 laps it took the fastest champ sled 3 laps to get past the F5 sleds. and a F5 finished third. gear the edge based sled 22/40 pick up the engagement some. this is a piston port motor so a inherent bog down low is the norm. helix change will make a big difference in these. our 2003 indy 500 basically stock other then gearing/clutching with my 100 pound daughter on it won many 500 c.c. class wins. even over 500 xcsp in short run's. we also placed 2nd at a ice radar run with a 1977 TXL 340 in the 500 class. a F5 cat beat us by 1 mph. that TXL won it's class in eagle river 6-7 years ago. the 500 is basically a 340 big bore. and the TXL 340 was another winner as far as reliability. the 1977 Polaris race team ( the midnight blue express) 340 super mod. motor is based off that same TXL 340 these were 92 h.p. and still the most reliable motor on the track. and won just about every time it was on the track.