Discrepancy in Engine CC Numbers?


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Hello everybody. I need some knowledge about engine cc. For e.g hero karizma bike is 250 cc but in actual it is 223cc. Why is it so ? Where is the remaining 27cc? Even pulsar 150cc actual has 143cc. What is the reason behind this? Why dont they make complete 250cc or 150cc ?
 
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Re: Engine's cc difference.

Hello everybody. I need some knowledge about engine cc. For e.g hero karizma bike is 250 cc but in actual it is 223cc. Why is it so ? Where is the remaining 27cc? Even pulsar 150cc actual has 143cc. What is the reason behind this? Why dont they make complete 250cc or 150cc ?
Engines have to maintain Bore/Stroke ratio to balance rpm and torque. The Bore/Stroke ratio is either close to 1 (Square), Close to 2(Over square) or close to 0.4 (under square). If we take Karizma, the bore to stroke ratio is 6.55/6.62 = 1.004. If 250 cc is needed, Stroke has to be 7.41 cm. The bore/stroke ratio will then become 6.55/7.41 =0.88 and will change the nature of engine. It will also require non standard pistons.
 

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