Re: Big 6 compression

["James Moran" <jmoran@xxxxxxxxx>]

Umm, compression ratio is a comparison of the volume in the combustion
chamber and cylinder at BDC and the volume in the combustion chamber and
cylinder at TDC.  With valve timimg events, there is no way to compare
static compression ratio with the numbers from a compression test.

The M30 engine in the 1988 535is has a compression ratio of 8.5:1 (IIRC),
which when multiplied by 14.7 gives 125 psi.  Nowhere near 150 psi.

Anyway, 150psi does sound reasonable.

Jim Moran
'88 M6

- ----- Original Message -----
From: Robert Rose <rarose@domain.elided>

> Jim,
>   I don't know specifics of that model, but they sound good. The engine
> is probably a 10.5:1 compression, which means 10.5 times 14.7psi (one
> atmosphere)=154psi will be the perfect ideal number. Your values are I
> dare say within the accuracy limits of your compression gauge. And more
> importantly all of the cylinders are even.
> --Rob
>   2001 330i
>   (just traded in my 2000 M roadster)
>
> > Date: Tue, 23 Jan 2001 00:20:07 -0500
> > From: flatthead@domain.elided
> >
> > I've always
> > thought the uniformity of the readings (no wild swings, especially
> > between the #5 and #6 cylinders)  is the most important thing, but I'd
> > like to know if 150 psi is a good reading.

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