dont try to do your own porting, it can totally screw up your engine. you have to know how far the piston travels up and down, when which valves need to be open and when to be closed and how long they need to stay open.also drilling them might make the sleeve less smooth, and if the piston scrapes against something it could wear away and you would loose compression. these engines operate under very igh tolerances and you need to know a lot about them before modding them yourself.