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5,298 Posts

4-cyl. displacement =

**πD²S**

**(pi x D-squared x S)**, where D is bore diameter and S is stroke length.

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5,298 Posts

4-cyl. displacement =

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146 Posts

Otto,

Shouldn't that be pi x r squared x S, or pi x (D/2 squared) x S.

Wayne

Shouldn't that be pi x r squared x S, or pi x (D/2 squared) x S.

Wayne

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5,298 Posts

Not quite, Grasshopper! That would be correct forwayne70gt said:Otto,

Shouldn't that be pi x r squared x S, or pi x (D/2 squared) x S.

Wayne

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5,564 Posts

D squared is FOUR times bigger than R squared .... so your formula quickly gives the displacement of a FOUR cylinder motor!

Why not use the bore size?

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146 Posts

I quess I should have spent more time on the message and less on the formula!

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5,564 Posts

Otto was only making the MATH simpler - not the MEASURING!nobody said:Why not use the bore size?

"piston size" is very close to bore size so makes very little difference to the answer BUT means you have to pull a piston to measure it instead of just getting the size of the bore!

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5,298 Posts

OK, OK, diameter of BORE then!nobody said:Why not use the bore size?

Was really just trying to point out that you don't have to halve the bore (radius), square it and then multiply it by pi and times four to calculate the four cylinder total bore area. (D/2)² = (D²/4) x 4 (cylinders) = D²! I digress.

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