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CCing a new bore

Discussion in 'The Garage' started by Larry Miller5509, Mar 14, 2016.

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  1. Larry Miller5509

    Larry Miller5509 XS650 Enthusiast

    How do you determin the cc's after boring an engine? I bored 2nd. oversize.
     
  2. madjap

    madjap XS650 Addict

    Height times radius times 3.14 is how you get cylinder volume BUT I'm not sure if a combustion chamber area is included in overall engine size CC's or not... So, basically... I've been almost no assistance whatsoever. Sigh.
     
  3. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Haha, madjap, using the wrong divining rods.
    This'n requires dangling a calculator from a piece of string.

    If you do it in millimeters:
    Bore * Bore * Stroke * Pi/4 = Displacement of one cylinder in cubic millimeters
    To get it in Cubic Centimeters, divide that mess by 1000

    Ex:
    Bore (2nd over) = 75.5mm
    Stroke = 74mm
    Pi/4 = (3.14159 / 4) = 0.7854

    75.5 x 75.5 x 74 x 0.7854 = 331296.2, then (divided by 1000) = 331.3cc
    Thats for one cylinder. Multiply by 2 to get total displacement = 662.6cc

    Compression chamber volume is not included when calculating displacement...
     
    Johnnny13 likes this.
  4. madjap

    madjap XS650 Addict

    Good LORD, I re-read my post this am and I hope to GOD no-one EVER follows my post-feverish advice on ANYTHING! I'm not even sure cats CAN fly now! Mr. Miller; take my formula, mix it with 2Many's, take all the math, crumple it up, throw it away. THEN, take 2Many's math and use IT while stomping your good foot on MY MATH (twice)...
     
  5. Larry Miller5509

    Larry Miller5509 XS650 Enthusiast

    That's a great formula. Thank you very much. I can always depend on everyone at Xs650 for those hard questions.
     
  6. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    We can simplify this even more.

    For our 2-cylinder XS650 engines, keeping with the standard 74mm stroke, you can simply use the bore (in millimeters) squared, times the constant of 0.116239 to find the displacement.

    (Bore) x (Bore) x 0.116239 = Displacement in CC's

    75 x 75 x 0.116239 = 653.84 cc

    Bore => Displacement
    75.00 => 653.8 cc (STD bore)
    75.25 => 658.2 cc (1st over)
    75.50 => 662.6 cc (2nd over)
    75.75 => 667.0 cc (3rd over)
    76.00 => 671.4 cc (4th over)
    76.50 => 680.3 cc (6th over)
    77.00 => 689.2 cc
    78.00 => 707.2 cc
    80.00 => 743.9 cc (750 kit)
    80.25 => 748.6 cc
    83.00 => 800.8 cc (Crazy big)
     
  7. ^ Good stuff there!
     
  8. 650Skull

    650Skull SSSSSSSSSlither Top Contributor

    I would have done it the lazy way.

    680cc is 6 over = 27cc larger than stock.

    6 over is 3 x 2,

    27cc divided by 3 = 9cc

    second over is 653cc + 9cc = 662cc.

    I know lazy and inacurate

    Have kept you formula for future..........thanks 2m
     
  9. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Haha, that's in my other book, SWEG, Scientific Wild Estimated Guesses.

    I use it for calculating restaurant tips...
     

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