When to do compression testing
February 29th, 2016, 07:21 AM
#1
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Location: Prescott Wash.
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When to do compression testing
I should know this but age and time has taken my memory again.
To get a good feel for condition should I take them cold and at normal temp.?
I have a 350 with #8 heads (don't know the type of pistons yet) The motor has been replaced (says prior owner) about 10,000 miles ago. What should I be seeing as far as compression?
To get a good feel for condition should I take them cold and at normal temp.?
I have a 350 with #8 heads (don't know the type of pistons yet) The motor has been replaced (says prior owner) about 10,000 miles ago. What should I be seeing as far as compression?
March 1st, 2016, 05:15 AM
#2
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Location: Melville, Saskatchewan
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Warm, throttle wide open and all plugs removed with the ignition disconnected. My stock internal #8 headed 350 with a Performer cam had 140-142 psi all 8 cylinders. It also has 15-20 psi hot idle oil pressure, 45-50 cruise and 60 cold oil pressure. Put an oil gauge on it as well. I have found the mid 70's 350's very reliable and adequate power, especially for their time. It was a 75 Cutlass 4 door, 350 Rocket powered that our family owned that turned me on to Oldsmobile's.
Last edited by olds 307 and 403; March 1st, 2016 at 05:18 AM.
March 1st, 2016, 07:51 AM
#3
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You can also do the test dry, and then add a couple of squirts of oil in each cylinder and repeat to determine if the rings are bad. Leak down tests are a good trouble shooting aide if your trying to isolate cylinder issues also.
March 1st, 2016, 03:03 PM
#5
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For a factory engine, what olds 307 and 403 posted sounds right. Be aware that cylinder pressure is controlled not only by the static compression ratio of the engine but also by the camshaft profile. This means two engines with the same CR but different camshafts can have drastically different pressure readings.
Without knowing what pistons or camshaft are in there you should be looking for consistent readings from cylinder to cylinder.
Without knowing what pistons or camshaft are in there you should be looking for consistent readings from cylinder to cylinder.
March 9th, 2016, 02:24 PM
#7
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My compression test results
I did my compression test before the teardown. Stone cold WOT all cylinders average 145 psi. lowest 140 highest 150 . Could not do a test with it warm. So for a remanufactured engine was said it had about 10,000 miles on it. The gauge I had was not the best but was a screw in. How do these numbers sound?
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