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331 Marine Hemi

Posted: Mon Mar 14, 2011 2:22 pm
by S&S
Does anyone know what the compression pressure is for these engines?
Thanks!

Re: 331 Marine Hemi

Posted: Tue Mar 15, 2011 4:17 am
by mart
The factory specs show 8.2 to 1. That's nominal though and assuming the deck
height, gasket thickness and cylinder
head CC's are right on spec. With
normal production tolerances, the
actual compression ratio is likely
anywhere from a half to a full point
lower.

mart
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Re: 331 Marine Hemi

Posted: Tue Mar 15, 2011 8:59 am
by S&S
Thanks mart, but I'm looking for the test gauge pressure range (want to see if I need to do rings or not)

Re: 331 Marine Hemi

Posted: Wed Mar 16, 2011 12:07 pm
by BlueDjinn
Compression pressure of 331 with 7.5:1 ratio is 135 psi minimum.
Compression pressure of 331 with 8.5:1 ratio is 140 psi minimum.

Whenever I do a cylinder pressure test on any engine I just check each cylinder while looking for a certain consistency
between readings. After I have my readings I look up the spec to see how they compare. A serious discrepancy denotes a problem and it isn't always just rings. I've had readings significantly higher than spec which turned out to be a valve problem; not opening.
I've also had pressure readings so low as to not support the combustion event. Once again a valve; not seating properly; bent or burnt.
Of course it could also be nothing at all to do with rings or valves.
Anyway, 135-140 psi as reference will expose the offending cylinder(s).

Re: 331 Marine Hemi

Posted: Thu Mar 17, 2011 6:01 pm
by Beltran
The copper gaskets they used to use are notorious for leaking coolant / water. I just tore apart two engines that were both leaking between the cylinder walls.

Re: 331 Marine Hemi

Posted: Mon Mar 21, 2011 2:42 pm
by S&S
Thanks!