Discussion in 'The Garage' started by Larry Miller5509, Mar 14, 2016.
How do you determin the cc's after boring an engine? I bored 2nd. oversize.
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.
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
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...
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)...
That's a great formula. Thank you very much. I can always depend on everyone at Xs650 for those hard questions.
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)
^ Good stuff there!
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
Haha, that's in my other book, SWEG, Scientific Wild Estimated Guesses.
I use it for calculating restaurant tips...
Oh that's good
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