Hi, i have a honda 250R all nice and modded but i want more out of my motor and cant afford a cylinder kit yet. i have a 72.25mm piston in it right now and i was told it was a 295. i want to step it up to about a 310 and im looking at these two piston sizes: 73mm(.040 over) and 73.5mm(.060 over)i would like to know what size motors would these size pistons would make it . for example , i was thinking that the 73mm was a 310 but i have no idea. Please fill me in. Thank You.

 

I have been told by my engine builder that the 310 is realy a 295 and they call it a 310. This is what he tells me. The 310 is the finail overbore.
The rule when boring any 2-stroke is to only go to the next overbore unless the liner does not clean up. By you want to skip sizes to go up to 73 or 73.5mm you will run out of bores and then you will have to either buy a new cylinder or get it selveed. Going up just the few cc's does not give you any more power. Any good engine builder will tell you that.

 

Based on a stock stroke of 72 mm your current bore would give you:
295.3 cc sq.

going to 73.5 mm bore would yield: 305.6 cc sq.

 

thanks guys.[img]i/expressions/face-icon-small-happy.gif[/img]