Compression test results Should I be worried
Thread Starter
Launching!
Joined: May 2012
Posts: 235
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From: Gurnee IL
Compression test results Should I be worried hey guys did a compression test today and all cylinders are at 150psi. Car does have a btr stage 4 cam ported 243 heads unmilled stock ls1 bottom end . Is this normal or not test was done dry on a cold engine with throttle at wot.. and the gauge never lost any psi spark plugs was black and had fresh oil on them btw
Staging Lane
Joined: Mar 2019
Posts: 57
Likes: 2
Anything under 140psi across the board or more than a 10-15psi difference is “bad” compression for most modern motors.
if there is a special ratio on the LS I’m sure someone will correct me. But those numbers look perfectly fine as a general standard.
Consistsncy between all the cylinders is the most important. As long as it’s not SUPER low.
it will also vary depending on your compression ratio/heads.
if there is a special ratio on the LS I’m sure someone will correct me. But those numbers look perfectly fine as a general standard.
Consistsncy between all the cylinders is the most important. As long as it’s not SUPER low.
it will also vary depending on your compression ratio/heads.
Thread Starter
Launching!
Joined: May 2012
Posts: 235
Likes: 0
From: Gurnee IL
Anything under 140psi across the board or more than a 10-15psi difference is “bad” compression for most modern motors.
if there is a special ratio on the LS I’m sure someone will correct me. But those numbers look perfectly fine as a general standard.
Consistsncy between all the cylinders is the most important. As long as it’s not SUPER low.
it will also vary depending on your compression ratio/heads.
if there is a special ratio on the LS I’m sure someone will correct me. But those numbers look perfectly fine as a general standard.
Consistsncy between all the cylinders is the most important. As long as it’s not SUPER low.
it will also vary depending on your compression ratio/heads.
TECH Resident
Joined: Mar 2012
Posts: 858
Likes: 402
From: Texas
I'm not familiar with the exact profile of your cam, but 150 psi with a big cam is not uncommon; remember, big cam usually equals more overlap, which means lower cranking compression.
I'd consider 150 psi to be the lower limit of a good running engine, but "good" just the same, depending on the other variables.
You said that the pressure was even across all eight cylinders, so that is a really good sign.
The only thing that would make me curious is that you said there was fresh oil on the plugs.
How many miles do you have on this shortblock?
I'd consider 150 psi to be the lower limit of a good running engine, but "good" just the same, depending on the other variables.
You said that the pressure was even across all eight cylinders, so that is a really good sign.
The only thing that would make me curious is that you said there was fresh oil on the plugs.
How many miles do you have on this shortblock?
TECH Junkie
Joined: Jun 2008
Posts: 3,202
Likes: 1,390
From: Nitro Alley
I am not familiar with the specs of the camshaft being used...
However, it is more than likely that the valve events are "bleeding off" the dynamic compression ratio.
Thus giving you the 150.00 PSI found.
As states by ck 32... good news is that all cylinders show aprox. equal pressure.
More than likely everything is fine.
However, it is more than likely that the valve events are "bleeding off" the dynamic compression ratio.
Thus giving you the 150.00 PSI found.
As states by ck 32... good news is that all cylinders show aprox. equal pressure.
More than likely everything is fine.
Thread Starter
Launching!
Joined: May 2012
Posts: 235
Likes: 0
From: Gurnee IL
I'm not familiar with the exact profile of your cam, but 150 psi with a big cam is not uncommon; remember, big cam usually equals more overlap, which means lower cranking compression.
I'd consider 150 psi to be the lower limit of a good running engine, but "good" just the same, depending on the other variables.
You said that the pressure was even across all eight cylinders, so that is a really good sign.
The only thing that would make me curious is that you said there was fresh oil on the plugs.
How many miles do you have on this shortblock?
I'd consider 150 psi to be the lower limit of a good running engine, but "good" just the same, depending on the other variables.
You said that the pressure was even across all eight cylinders, so that is a really good sign.
The only thing that would make me curious is that you said there was fresh oil on the plugs.
How many miles do you have on this shortblock?
Thread Starter
Launching!
Joined: May 2012
Posts: 235
Likes: 0
From: Gurnee IL
I am not familiar with the specs of the camshaft being used...
However, it is more than likely that the valve events are "bleeding off" the dynamic compression ratio.
Thus giving you the 150.00 PSI found.
As states by ck 32... good news is that all cylinders show aprox. equal pressure.
More than likely everything is fine.
However, it is more than likely that the valve events are "bleeding off" the dynamic compression ratio.
Thus giving you the 150.00 PSI found.
As states by ck 32... good news is that all cylinders show aprox. equal pressure.
More than likely everything is fine.
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Brett Foote Thread Starter
Launching!
Joined: May 2012
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From: Gurnee IL
TECH Addict
Joined: Oct 2016
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From: PDX-OR-USA
IMHO,, Compression tests are kinda the "check engine" light,,, the real test is the leak down.
Was the test done wet or dry?
FWIW when I'm trackside I don't even have a compression tester in my toolbox I have a leak down tester..
Some cars get a leak down between sessions.. It will catch valves letting go before its a bad thing..
Was the test done wet or dry?
FWIW when I'm trackside I don't even have a compression tester in my toolbox I have a leak down tester..
Some cars get a leak down between sessions.. It will catch valves letting go before its a bad thing..
Thread Starter
Launching!
Joined: May 2012
Posts: 235
Likes: 0
From: Gurnee IL
IMHO,, Compression tests are kinda the "check engine" light,,, the real test is the leak down.
Was the test done wet or dry?
FWIW when I'm trackside I don't even have a compression tester in my toolbox I have a leak down tester..
Some cars get a leak down between sessions.. It will catch valves letting go before its a bad thing..
Was the test done wet or dry?
FWIW when I'm trackside I don't even have a compression tester in my toolbox I have a leak down tester..
Some cars get a leak down between sessions.. It will catch valves letting go before its a bad thing..
LS1Tech Sponsor
Joined: Jan 2008
Posts: 2,232
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From: Ohio, Georgia, Nevada, Texas
As others have said, as long as the are fairly equal...that's what's important. The big cams close the intake valves later and the cylinder can't begin to build compression until it does. Hence the lower measurement.
