i knew a 50cc racing pro that changed his cylinder and rings like every couple of races. he's got drawers full of pistons and cylinders, all marked up with sharpie indicating the hot points and wear marks, carbon buildup, squish zones. He's got binders full of info on engine setups based on track, weather condition, temperature, etc....(he takes meticulous notes).
according to him, these cheap race kits ($250 may not seem cheap to you or me, but pro racers will spend thousands) these cheap kits were made to be raced only a couple of times before being thrown away.
I'm approaching 9,000 miles on my Polini.