[Diy_efi] Compression pressure (off topic)

[Mike]

I seem to recall tests should be done on a hot engine and perhaps with
a teaspoon of oil first poured into chamber (to diagnose leaky rings) and
when I did mine I got *voila* my indicated cr to within +- 5%  based on
data in my service manual !

rgds

mike




At 09:00 PM 2/13/07, you wrote:
> This is off topic but there are so many well-experienced "engine people" here it is worth asking.
> Is there a table or formula to get a "rough guess" about the static compression ratio of an engine, based only on measured compression pressure? This is assuming the engine is in good mechanical shape without compression leaks.    In other words, if you measure 145 PSI on a compression gauge during cranking, is there a way to make an educated guess about the C/R of this engine?
> Certainly cam profile matters bigtime.  I'm thinking about mild and stock cams here.  It would make sense that dividing by atmospheric air pressure (14.7) would give you a general idea but that wouldn't take into account air cooling during compression or other losses.
> Any thoughts?
>David
>
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Regards from


Mike
Perth, Western Australia
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