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Thread: Cubic Inch Formula ?

  1. #1
    sawtooth
    Looking for a little help here, what is the formula to figure out the cubic inchs of a motor like when you want to make one bigger. It was something like stroke x rod length x cylinder diameter x blah blah blah = cubic inch. It was explained to me years back and I will be damed if I can remember.....should have wrote it down. Thanks to all the smart guys that can help me with this.

  2. #2
    Fiat48
    Bore x Bore x stroke x7854 x # of cylinders.

  3. #3
    Senior Member
    Join Date
    Feb 2009
    Posts
    2,626
    Sawtooth, check out the first thread in this forum. It is called "Tech Links". There are links there to tons of info including this. BRC Engine Calculators (http://www.brcperformance.com/enginecalc.htm)

  4. #4
    BDMar
    CI = (bore/2 x bore/2) x 3.1416 x stroke x # of cylinders
    Ex:
    4.500 bore
    4.250 stroke
    (2.250 x 2.250) = 5.063
    5.063 x 3.1416 = 15.906
    15.906 x 4.250 = 67.601
    67.601 x 8 = 540.808 CI

  5. #5
    BDMar
    HAHA Two replies while I was typing my formula!!

  6. #6
    BDMar
    Bore x Bore x stroke x7854 x # of cylinders.
    I think you meant .7854

  7. #7
    Infomaniac

  8. #8
    superdave013
    Radius of cylinder squared X pie X # of cylinders.
    Not bad for a guy who's math classes were always right after lunch.

  9. #9
    obnoxious001
    Radius of cylinder squared X pie X # of cylinders.
    Not bad for a guy who's math classes were always right after lunch.
    You have been eating too much PIE!
    That formula gives you the total surface area of the tops of the pistons if they were flat tops with no valve reliefs. pi x r squared gives you the area of a circle.

  10. #10
    River Rat 005
    Superdave you must have been late that day. You need X stroke=cid

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