Compression ratio is the difference of the total volume
in one cylinder between piston at bottom and piston at
top. A 0.030" overbore (if the pistons have the same top
as before) makes a very, very small difference in CR.
Thomas
>
>
> TCR2B@aol.com wrote:
>
> > Adam,
> >
> > A couple of things:
> > New bore dia. = 78.762 mm
> > 1mm=.03937in.
> > .030/.03937=.762(mm) oversize
> > Your displacement calculation appears to be correct:
> > it was easier for me to figure it in inches and then convert back to mm
> >
> > displacement=volume x 4
> > volume=area x height
> > area=pi x r (squared)
> >
> > 77.6 / 25.4 = 3.0551 in (stroke value) [height]
> > 78.762 / 25.4 = 3.100 in
> > 3.100 / 2 = 1.550 in (radius value of bore)
> > 1.550 x 1.550 x 3.1415 (pi) = 7.5474 cu. in.
> > 7.5474 cu. in. x 3.0551 = 23.0573 in. cu. (per/cylinder)
> > 23.0573 x 4 (cylinders) = 92.229 in. cu.
> > 1 liter = 1000 cc ~ 61 in. cu.
> > 92.229 / 61 = 1.511 liters = 1511 cc
> >
> > As far as compression ratio goes: this hasn't changed at all. Compression
> > ratio is a function of stroke at top dead center (high as the piston goes)
> > vs. bottom dead center (as low as piston goes). You've changed the bore
> > diameter, not the stroke.
> > Some of you other old-timers can check me on this, I believe I'm right.
> >
> > Mike Davenport
> > '67 1600
> > President - Rustburg Roadsters Club
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