On Sat, 20 Sep 1997 21:55:31 +1300 Karl Gilchrist
<xtr25618701(at)xtra.co.nz> writes:
>Does any one has a formula that converts compression test figures into
>a compression ratio. Today I tested the compression and all pots were
>at
>177 (?units) is there some way I can convert this to a compression
>ratio
>eg 1:9.5. BTW what is normal for our engines.
>
>Karl
Karl, there just is no formula to calculate CR from compression pressure
data.
The reason is that blow-by, and cam overlap wont let you see realistic
pressure figures until the engine spins to around the RPM where the
engine makes PEAK torque.
This is the RPM where the overlap doesnt cause the compression
pressures to falter.
BTW, a hot cammed 11/1 motor may only net 120 or 130 PSI,
where a mild cammed 9/1 motor nest 180 PSI.
177 PSI, if consistant across all 4 cyls, is a pretty good figure,
and
indicates that your rings seal well, valves arent burnt, and
that the over all condition of the motor is likely good.
Jarrid Gross
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