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Old 03-06-2010, 08:45 PM
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bairdco bairdco is offline
a guy who makes cool bikes
Join Date: Aug 2009
Location: living the dream in southern california
Posts: 6,257
Default Re: Why are the engines called 66cc/80cc need info

Formula to figure engine cc displacement;
( multiply 3.142 x radius of bore mm squared x stroke length mm divided by 1000. )

To figure displacement for this example: 47mm bore x 38mm stroke;

Bore diameter divided by 2 = 23.5 mm radius
To square radius multiply 23.5mm x 23.5mm = 552.25 radius mm squared
552.25mm x 3.142 = 1735.17mm
1735.17mm x 38mm = 65936 cubic milliliters;
To get cubic centimeter divide 65936 by 1000 = 65.936cc or round off to 66cc

By western standards the volume of the engine head combustion chamber is not figured in the displacement engine rating, however some Chinese factories include this volume in their engine displacement ratings therefore making the engine appear bigger than it actually is.
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