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Thread: cylinder sizes

  1. 02-20-2012 08:17 PM #1
    chrs [OP]
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    cylinder sizes

    Ok help me please. If my bike is .40 over from stock, what size bike would I have? Never understood this part.
    Can you feel the power!
    87 250r
    Trx 5 pipe
    01 cr ignition from BDT
    38mm air striker
    Cool head
    Boyese rad valve
    87 250x
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  2. 02-20-2012 08:26 PM #2
    deadly
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    Quote Originally Posted by chrs View Post
    Ok help me please. If my bike is .40 over from stock, what size bike would I have? Never understood this part.
    Not sure what size the piston is but if you know you can use the following thread to calculate it.
    Calculating Bore Size?
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  3. 02-20-2012 08:32 PM #3
    chrs [OP]
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    Kinda confusing bore x bore x stroke ? Everything is stock, just .40 over
    Can you feel the power!
    87 250r
    Trx 5 pipe
    01 cr ignition from BDT
    38mm air striker
    Cool head
    Boyese rad valve
    87 250x
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  4. 02-20-2012 08:42 PM #4
    bsmith106
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    .040 overbore=1mm. Stock bore is 66mm+1mm=67mm. You want to know cubic centimeters. 10mm=1cm so move decimal point left. 67mm=6.7cm. So assuming stock72mm stroke your displacement=6.7x6.7x7.2x.7854=253.84cc. Bore times bore times stroke times.7854=displacement.
    Last edited by bsmith106; 02-20-2012 at 08:47 PM.
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  5. 02-21-2012 06:25 AM #5
    chrs [OP]
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    That makes a little more sence.
    Can you feel the power!
    87 250r
    Trx 5 pipe
    01 cr ignition from BDT
    38mm air striker
    Cool head
    Boyese rad valve
    87 250x
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  6. 02-21-2012 11:13 AM #6
    acecarlos
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    Look at it this way; for every +1MM you go in bore size with the stock stroke of 72MM (like from 66MM to 67MM or 68MM to 69MM), you gain an average of 7.5CC (7.5CC to 7.7CC).

    Stock CC at 66MM x 72MM is 246.3CC, add 7.5CC for every 1MM increase in bore size to 69.50MM...

    Your 67MM x 72MM = 246.3CC (stock CC) + 7.5CC (+1MM) = 253.8CC

    Carlos.
    WWW.BDTMOTORSPORTS.COM 909-466-9152
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