Figuring displacement?

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pi * radius^2 * stroke * no. cylinders

... or you can use a java calculator like the one on this web page.

hp math
 
Thank you guys. I always wanted to know (for example ,what 0.30 over would add to the displacement) and BJR, that`s easy to remember!
 
BJR's equation only works for a 8 cylinder engine. So all you /6 guys don't get excited if you plug in .030 overbore with a stock stroke on a 225 and come out with 300 cubic inches.
 
GotDart , your formula is more universal and the link to the math site is very helpful for more than just figuring displacement. Thanks
 
Bore x Bore x stroke x 3.14 x # cylinders = cubic inch
This works on all #'s of cylinder motors.
 
intimidator said:
Bore x Bore x stroke x 3.14 x # cylinders = cubic inch
Click to expand...
No it doesn't. If it did, my stroker would be 1664 cubic inches.

4.07 * 4.07 * 4 * 3.14 * 8 = 1664.4​


As I originally stated, the correct formula uses Radius squared... Radius is equal to Bore divided by 2.

(4.07/2) * (4.07/2) * 4 * 3.14 * 8 = 416.1​


If you use BJR's shortcut...

Bore x bore x stroke x 6.2832=CI​

... the number of cylinders must be 8. The reason is because Bore is equal to Radius times 2. So his formula is really...

(2 * Radius) * (2 * Radius) * Stroke * (2 * Pi) = ci​

And when you simplify that, the 2 * 2 * 2 becomes 8.
 
I'm sorry it was suppose to be Bore x Bore x .785 x Stroke x # cylinders. To much Chrismas cheer! LOL. Got Blueberry pie caught in my eye teeth and couldn't see what I was typing.
4.07 x 4.07 x .785 x 4.00 x 8 = 416.11027
 
You are incorrect GOTDART. BJR's formula is right. 6.2832 (8 cyl.) is pie doubled. Half (3.1416 pie) for 4 cyl. and 75% (4.7124) for 6 cyl.
Bore X Bore X Stroke X constant. 6.2832 (8)
4.7124 (6)
3.1416 (4)
Terry.
 
Only one constant to remember with my formula. .785 as long as you know how many cylinders you have. LOL
 
headsbikesmopars said:
You are incorrect GOTDART. BJR's formula is right.
Click to expand...

:scratch: I never said BJR was wrong. I said his equation was for an 8 cylinder engine. You just said the same thing. How is that incorrect?
 
My mistake. I thought you said BJR was correct ONLY with 8 cyl.'s. He (BJR) IS correct if you use the correct constant (# cyl's). I have used many formula's over the past 35 years and the one BJR uses is the one I use. It is fast, easy AND accurate. Shorter is what I should say. Only four entries and you have results. The busy man's formula, if you will. Terry.
 
headsbikesmopars said:
Shorter is what I should say.
Click to expand...
Thats why I use the formula I use. I only have to remember the .785 number. That is as long as I can still count how many cylinders it has.
I don't like trying to remember the numbers to use for 4, 6, and 10 cylinder motors.
Bore x Bore x Stroke x .785 x # cylinders = cubis inches
 
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