I have a polaris xplorer 300 2 cycle. What do you guys think the biggest over bore I can do for max hp and not blow it up? Thanks.

 

Welcome to the forum! Go over size enough to clean up the bore if it needs a top end.You're just wasting a cylinder if you go out more than what's needed! You can go all the way out to 1.5 to 2 mm over stock bore,but then you have a paper thin cylinder wall that wont last! If you want more power go to a larger atv! OPT