I have a fully modded sport 400 you name it done .Only thing havent done is bigger piston. Was wondering if i would have to resleeve for a 85mm piston and would it be worth it or just go to 87. Looking at cost of money at momment.

 

Alot of people have found that going to a bigger bore doesnt do a whole lot. Knowing what I know now I wont big bore another one unless I run out of bores. You can go .020,.040,.060,.080,.140,.160,.180 overbore on the 400's. When you get to the .140 and up the pistons get real expensive and the clearance needed increases and they rattle quite a bit. If your at .080 right now and need to bore, it would be cheaper than resleeving or buying another jug. Also if you bore more than one size the porting needs to be redone to compensate and restore power levels.Bubba

 

yep,has it been told earlier,there is some choices for pistons bore,
a 85mm (.080) piston will give you a 398cc 2 stroke engine,add more throttle response and torque,but top end is not that great,but is shoift out real quick.