On Fri, 21 Nov 1997 22:55:26 -0800 Sergio Dimarmo <wanderer(at)sure.net>
writes:
>I have always done the test with throttle closed, thanks for the tip.
>I
>remember seeing something about Alpines with low compression pistons,
>could this apply to my Series V and if so what would be a normal
>reading
>with these pistons?
>
>Serg
I dont think you would find an alpine low compresion engine in the US.
Perhaps if it were taken from a iron headed Hillman.
You are in the States right?
Open the throttles and retest, your old figures mean absolutely nothing.
Leaving the throttles closed does not let the engine get a full gulp
of 1 bar air, so the compression pressures are lower than they
would be with the full gulp.
As for the low compression figures, it would be reasonable to derate
the compression figures by the ratio differences.
So.....
Assuming that high comp ratio is 9.2 and low is 8.0, and high compression
cranking pressure should be around 160 PSI,
(8.0 / 9.2) * 160 = 140 PSI.
This should hold to be true, but wont work for all engines particularly
higher performance ones, where the engines volumetric efficiency
is very low at cranking speeds due to valve overlap.
Jarrid Gross
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