How to figure out engine displacement

[beerock]

This is for everyone who want to figure out there actual displacement size.

In this example I used a 67.75mm piston.

Just plug in your piston size and there ya go.

divide piston size by 2 (67.75mm(my piston = 33.875mm)

then convert to centimeters(move the decimal point over a place) 3.3875mm

multiply by stroke converted to centimeters (72mm= 7.2mm)

3.3875mm x 7.2mm = 24.372mm x Pie(3.14) = 76.5846mm x 3.3875(displacement size = 259.4303325)CC

convert milimeters to inches divide milimeters by 25.4

convert thousanths to milimeters multiply by 25.4

[TX400ex-250r]

this is way easier
http://www.bgsoflex.com/displacement.html

[beerock]

computers arent always around.

Mechanics know this stuff and use calculators or paper.:macho

[dober250R]

I always just use some digital calipers and push the lil mm button.:macho

[baseballplaya23]

how do you know or figure out your stroke?

[bwamos]

Legend:

b = Bore
s = Stroke
d = Displacment
^2 = squared
* = multimply
/ = divide
sqrt = square root

Use mm for the unit of measure.

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Bore & Stroke to Displacement:
(0.5b^2)*3.14*s=d

Bore & Displacement to Stroke:
d / ((0.5b^2)*3.14) = s

Displacement and Stroke to Bore:
2 * sqrt (d / 3.14s) = b

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To go from mm^3 to cm^3 (CC) you need to divide d by 1000 or multimply by 1000 (10x10x10) to go from cc's to mm^3 for d.

d in these equations need to be in mm^3. So if you want 330cc you need to use 330,000 mm^3

[beerock]

Originally posted by baseballplaya23
how do you know or figure out your stroke?

usually the engine oem specs tell you your stroke.

forgive me guys I wrote bore where it should have said displacement, I edited it.

[slick250]

If you are figuring your stroke from scratch and dont know the stock stroke or are just not sure if it is stock, find top dead center and mark the piston height in the cylinder. Rotate the crank to bottom dead center and measure the distance traveled. That is the stroke.;)

[2004exrider]

Heres another way...
http://www.freewebs.com/rideyellow04/techpagefaqs.htm

Jimmy

[jeepman]

I was wondering if you could tell me what my displacement is cause i bought an are with a motor that is bored over 90 so can u tell me what the displacement is

[droppedmazda]

this is an easier way:
bore x bore x stroke x .7854 = total displacement