Hello everyone, this is my first post on this mailing list (I am also
a member of the Mopar Mailing List) and even though I don't have a
dakota I love to hear theoretical discussions about engines and cars
and trucks. This higher pressure measured by the compression tester
than the computed pressure based on the compression ratio got me
thinking.
Perhaps the pressure tester has higher psi than the compression ratio
would predict because the fitting that screws into the spark plug hole
takes up more volume inside the combustion chamber than the spark
plug, yielding a higher compression ratio while it is in there (the
spark plug displaces less volume while screwed in then the fitting for
the compression tester while screwed in).
I guess that would be a quick and cheap way to bump up the compression
ratio (slightly, of course), a plug company could make a spark plug
that takes up the most volume without causing piston interference and
the compression ratio would go up .3 or something.
The only other explanation I can think of is that the piston moves so
fast it produces a pressure "wave" that slaps into the gauge and gives
a momentary higher pressure (due to its velocity) than the average
pressure in the cylinder.
Anyone think this is likely?
-kipp leland (in digest mode)
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