PISTONS: Convert Piston Size (in mm or bore) to cc's

[300exHILLER]

I seen on the power roll site that is 76mm for their 297cc kit. But then I go on other sites like FST and Sparks and they say that their 76mm/.080 is a 330 kit. I went on moto-man.com and looked up pistons their chart says: 74mm=std, 74.5mm=.020, 75mm=.040, 75.5mm=.060, 76mm=.080. I need to know what bore I need to get up to 300cc's and NOT!!! over cause cause thats the rules for the MX series I race???

Another question what is the best (internal) motor work I can do for the $$$$ and stay under 300cc's???? What brand names, prices and where I can find it???

[300exHILLER]

HELP!!! ANYBODY

[powerslider]

Bore x bore x stroke x .0007854 = cc disp.

[gojk]

The 76mm will put you right at 297cc. The different size pistons making different displacements is probably them changing the stroke also.

[tprender]

Check the rules for where you are racing. The class limit might be 300cc, but see or ask if there is the .080 overbore.
You can use the formula that he gave or the one that I use is
pi*r*r*stroke*16.387= cc
both formulas will give the same answer
Some of the engine builders will cheat on the numbers for there engines to help make it sell better.

[300exHILLER]

ok thank you guys.


I planning on 11:1 76mm piston.
What cam should I go with?
Anything else that's the best power for the dollar???

[TRX_Thumper]

ok first of all FST's 330 kit uses stock rod...i was thinkin it was 80mm...maybe a misprint?

[300exHILLER]

on powerroll's site they state that a 80mm piston is 330cc's with a stock rod. 78mm is a 313cc.

[440exnacsracer]

since your running a smaller 4 stroke, i would get the highest lift, longest duration cam that WEBCAM makes and get hardfaced rockers, valve springs and shortend valve guides. then port/polish the head, bigger carb, yoshimura full exaust, K&N filter...youd have one fast bike then!

[300exHILLER]

sounds good. I already have a sparks X-4 and a k&n Thinking of running a 400ex stock carb. anybody else just getting opinions