AHHHHH!!!!!!!!!!
that is how you do it
you are recompressing already compressed air. in that case you can
do it. i
never did a compression test and i thought you only cranked it once.
when
you r driving, all that the engine will compress to will be the
theoretical
value(about 135-140 psi) in that case you won't lose any power if
you start
out with 160 psi and drop to 145 psi cus no air will squeeze past
the rings
at either the engine with 160 psi or 145 psi. it doesn't leak until
the
pressure reackes the measured pressure and when you drive it won't
go over
140. therefore 140 psi is great and will run as good as an engine
with
200+psi
I disagree with the idea that you are compressing compressed air in
the compression test with each continued compression stroke. A four
cycle engine isn't like an air compressor. Read this carefully.
An air compressor is has two phases. The down stroke brings in air and
the up stroke pushes it into the tank, the next down stroke brings in
more air, the next up stroke pushes it into the tank. Notice, it does
_not_ compress it. The air is MOVING THROUGH A VALVE into the tank.
IN a car, the air moves nowhere during the compression stroke. The
cycle on an air compression is exhaust, intake, exhaust, intake.
A four stroke engine brings in air on the down stroke, compresses it
on the upstroke, then an expansion stroke ___where the piston moves
down and the compressed air returns to its original volume___ (--in
other words, it theoretically returns the gas in the cylinder to its
original pressure) then goes up again to exhaust that gas. Pressure
is not being added to continuously like an air compressor. Without a
piston firing, it goes like this: compressed, EXPANDED, exhausted,
intaked, compressed, expanded, exhausted, intaked....
An air compressor can never get a pressure in its reservoir over the
pressure of its compression ratio (theoretical value). It just holds
more volume because the air is NOT compressed INSIDE the the cylinder
but pushed from the cylinder to the tank. How could it get higher
pressure than its compression ratio? That would say that air flows
from low pressure to high!
When doing a compression test you crank the engine a few times because
the first compression stroke might be incomplete (the piston may have
been halfway into the compression stroke before the engine turned) and
because the first compression stroke may be slower as the starter
starts to turn the engine. If cranking it more times kept adding to
the pressure, eventually if you cranked it enough enough pressure
would build up to max out the tester! If that was the case, you would
have to carefully count the number of compressions cycles if you
wanted equal pressure readings from all cylinders (a pressure test on
a cylinder with three compression cycles would not be comparable to
the next cylinder with four compression cycles)
Plus, in a compression test the pressure stops going up after a
couple engine revolutions, which wouldn't happen if each stroke
compounded the other.
The check valve on the compression tester simply lets more in if the
pressure on the next compression stroke is higher than the pressure
before.
You get it? Just writing this has cleared up a lot in my mind
regarding this issue. The four stroke cycle may pump air, but this is
out of the exhaust valve and is not easily measurable. What the
compression tester tests is the _peak_ pressure during the compression
phase. It reads the highest pressure before the piston starts to go
down and the pressure returns to its original level during the
expansion phase.
just my 300 pesos (.02b)
-kipp leland
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