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Old 10-25-2008, 01:37 PM
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how to calculate engine size with different bore sizes???

I was wondering how u would calculate what size an engine is after it has been bored out??? I know bbc Have a 3.75, 4.00 and a 4.25 stroke. When U bore it 30 60 90 or 120 over how do you figure out what size it is???
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Old 10-25-2008, 02:33 PM
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The formula is Pi X the radius squared Time the stroke Xnumber of cylinders
so on a 350 chevy
3.1417 X 4 X 3.48 X8 = 349859


Hope this helps
Chet
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Old 10-25-2008, 02:52 PM
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ok How do u come up with the first 2 numbers??? I am a little dumb as this???
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Old 10-25-2008, 03:28 PM
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Quote:
Originally Posted by inquiring_mind2
ok How do u come up with the first 2 numbers??? I am a little dumb as this???
I assume they are pi and radius squared. Although I tried it for my 318 and it showed up as a 332. But here is a site you can use
http://www.csgnetwork.com/cubicinchdispcalc.html
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Old 10-25-2008, 04:15 PM
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formula for displacement

(BORE)X(BORE)X(STROKE)X(.7854)X(NUMBER OF CYLINDERS)

EXAMPLE: 4x4 x 3.48 x .7854 x 8= 349.848576 round up 350ci

I've never heard the one using PIE, but it looks like it works... I just find this one a little more simple..
Danny
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Old 10-25-2008, 04:18 PM
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ok where does the .7854 come from
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Old 10-25-2008, 04:33 PM
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Quote:
Originally Posted by Fnix
I assume they are pi and radius squared. Although I tried it for my 318 and it showed up as a 332. But here is a site you can use
http://www.csgnetwork.com/cubicinchdispcalc.html
Your right, pie X radius squared X stroke X no. of cylinders.
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Old 10-25-2008, 05:17 PM
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.7854

I dunno, Some guy smarter then me. I just know it works and It's easier for me. If I works I don't question it.
If u got a gonkulator handy you can check it. It will be accurate every time. It came outta one of my books, Prolly David Vizard... I don't think any of us have a need to question him.

just try it.

383ci: bore is 4.030", stroke is 3.75"
406ci: bore 4.155" stroke 3.75"
434ci: bore " " 4.00"
302 : bore 4" stroke 3"
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Old 10-25-2008, 05:39 PM
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LOL OK thx sounds good to me
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Old 10-25-2008, 07:04 PM
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Quote:
Originally Posted by inquiring_mind2
ok How do u come up with the first 2 numbers??? I am a little dumb as this???
Pi is a mathematical constant - always 3.1417
The second number is the radius squared. The radius of a circle is 1/2 the diameter, in this case, 1/2 the bore. The stock bore of a 350 engine is 4.0 so 1/2 of the stock bore is 2 and 2 squared is 2 times itself or 2x2 which is 4.
Terry
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Old 10-25-2008, 07:22 PM
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Pi is actully 3.141592654.. it does continue, but no calculator can count that high. if you used 3.1417 the displacement would be off a little, it would be more accurate to use 3.14 only.
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Old 10-25-2008, 07:34 PM
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Quote:
Originally Posted by inquiring_mind2
ok where does the .7854 come from
Cylider volume = pi/4 x bore squared x stroke[list]
Pi/4 =0.7853982
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Old 10-25-2008, 08:05 PM
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ok thank you very much for all of your help
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