> Here is another link that discusses the orifice. I tried a leakdown
> test using my Sears compressor that has two gauges (tank and line
> pressure, obviously no orifice) and I got stable readings varying from
> 85 to 92%. Of course, my engine had compression readings that ranged
> from 75 to 110 PSI, and I could definitely hear the air coming out of
> various places for the cylinders with low compression/ leakdown rates.
> So I'm not sure if an orifice is absolutely necessary if you get a
> stable PSI reading. Perhaps others on the list who are more
> knowledgeable in this area could "pipe" in.
The problem I have is statements like "a new engine may lose 5% to 8% on a
leakdown test" (from the web page John cited). Let's say, for the sake of
argument, I have a perfect engine cylinder, except it has a .010" hole
through the piston. It seems clear to me that, assuming I get a constant
100 psi out of the regulator, I'll get a very different pressure reading
with a .010" orifice than with a .100" orifice. So, in order for "5% to 8%"
to mean anything at all, there has to be a standard for the orifice size.
And with no orifice at all, I'll get no pressure drop at all (again assuming
the regulator is perfect which of course they aren't).
I haven't tried it, mind you, but I'll bet I can build a system that will
show only a 5% pressure drop, with the spark plug adapter laying on the
floor ... of course first I'll need a really big air tank or a 1000cfm
compressor ... <g>
Randall
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