yz250f big bore kits

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Jan 12, 2001
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#1
Guys I got a question. I've tried to do some calculations. a 79 mm piston increases the bore to 262. So technically thats 6.5cc per mm. So my question is how does an 80mm piston from thumper racing come out to 277cc's as they claim? I would think the extra 1mm to the piston size from a 262 would work out to a 268. Can some one help me with this? As you increase piston size does the cc's increase exponentially? I'm just curious cause don't want to order a 280 kiton a 280 kit(277cc) and and get back a 268. Thanks for your help. I'm not sure the formula for engine cc's and I could be totally wrong on the 6.5cc's per extra mm of piston.

Mark
 

Faded

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Jan 7, 2003
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#2
Stock:
Bore: 77mm, Stroke 53.6mm
Displacement: 249.47ccs

Big Bores:
Bore: 78mm, Stroke 53.6mm
Displacement: 255.99ccs

Bore: 79mm, Stroke 53.6mm
Displacement: 262.60ccs

Bore: 80mm, Stroke 53.6mm
Displacement: 269.29ccs