> Bought my first compression guage. It is calibrated in psi. How do I
> determine the compression ratio? Ie. how do I convert x psi to n:1?
Well, atmospheric pressure is 15 psi (close enough for this calculation) so
10:1 compression ratio will give you 150 psi.
However, only a perfectly sealing engine will give you 150. figure at least
10% leakage, which would be 135 psi. If you can get 130 on all cylinders of a
10:1 engine you're doing fine.
The calculation of absolute expected pressure like this really isn't useful
except as a gross check that the gauge is working more or less OK. It's more
important that you get repeatable, uniform readings across the cylinders. If
your 10:1 engine gives you 115, 120, 120 and 125 that's pretty decent and not
cause for worry.
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