Ron :
I beg to differ. Displacement is exactly that : displacement. How much
volume the pistons displace in one complete revolution. Combustion chamber
volume (which normally takes into account the shape of the piston top) does
not affect displacement, nor does piston shape.
Displacement is Pi (3.141592...) * (bore/2) * (bore/2) * stroke. If bore &
stroke are inches, the result is inches cubed or cubic inches. If bore &
stroke are centimeters, the result is cubic centimeters.
To put it another way, you cannot increase the displacement of an engine by
only changing the pistons or head.
Randall
On Friday, April 30, 1999 2:37 PM, The Becketts [SMTP:hillman@bigpond.com]
wrote:
> Lar Kaufman wrote:
> > It's quite easy to figure out displacement if all you do is change the
> > stroke. Your current displacement is 100%. Multiply that times the
> > percentage of additional stroke, and add that to your original
> displacement.
>
> I don't think this is true - assuming we mean displacement to include
> combustion chmaber space as well. If we mean displacement to only mean
> that volume displaced by the pistons as they move, then it probably is
> true.
>
> If the combustion chamber in the cylinder head did not exist and the
> pistons had flat tops, it would be true because the cylinder would then
be
> a true cylinder. However, in the case of an engine, any depression or
hump
> in the pistons and also the combustion chamber volume has to be accounted
> for.
>
> If the combustion chambers space = A, the piston hump or depression = B
(+
> or -), and the cylinder vloume = C, then the engine capacity is equal to
> No. of cyls * (A + or - B + C).
>
> Increasing the stroke by X percent would change the formula to:
> No. of Cyls * (A + or - B + (C * (100+X)/100))
>
> Regards,
>
> Ron Beckett
> Editor / Webmaster, LandRover Owners Club of Australia
> Webmaster/Database Manager, Hillman Owners Club of Australia
>
>
>
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