[Diy_efi] Compression pressure (off topic)

David Allen davida1
Tue Feb 13 13:00:50 UTC 2007


  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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