compression test reading??
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Novice
Joined: Mar 2010
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From: usa
compression test reading??
I have about 300 miles on a 95 inch build I did. I put in SE 95 inch flat tops, Andrews 54 cam, SE Performance heads. Big boy calculator for this setup at 5200 feet (my elevation) says 155 PSI. My readings were 155 front & 150 rear. So it seems about right.
However when I first did the test I thought I was supposed to be somewhere around 190 because I forgot to input the right elevation. So I redid the test with a little added engine oil in each cylinder. My readings were 175 front & 170 rear. Does that mean my rings are not seated yet? Again I have about 300 miles on the build and the test actually came out right according to the calculator but the added PSI after oil was added worries me a bit.
However when I first did the test I thought I was supposed to be somewhere around 190 because I forgot to input the right elevation. So I redid the test with a little added engine oil in each cylinder. My readings were 175 front & 170 rear. Does that mean my rings are not seated yet? Again I have about 300 miles on the build and the test actually came out right according to the calculator but the added PSI after oil was added worries me a bit.
Last edited by hdrider53; Mar 8, 2011 at 05:32 PM.
Road Captain
Joined: Jun 2006
Posts: 581
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From: Portland, OR
I have about 300 miles on a 95 inch build I did. I put in SE 95 inch flat tops, Andrews 54 cam, SE Performance heads. Big boy calculator for this setup at 5200 feet (my elevation) says 155 PSI. My readings were 155 front & 150 rear. So it seems about right.
However when I first did the test I thought I was supposed to be somewhere around 190 because I forgot to input the right elevation. So I redid the test with a little added engine oil in each cylinder. My readings were 175 front & 170 rear. Does that mean my rings are not seated yet? Again I have about 300 miles on the build and the test actually came out right according to the calculator but the added PSI after oil was added worries me a bit.
However when I first did the test I thought I was supposed to be somewhere around 190 because I forgot to input the right elevation. So I redid the test with a little added engine oil in each cylinder. My readings were 175 front & 170 rear. Does that mean my rings are not seated yet? Again I have about 300 miles on the build and the test actually came out right according to the calculator but the added PSI after oil was added worries me a bit.
Did you repeat the pre-oil test, testing for repeatability?
What static CR were you shooting for?
What break-in method have you used? Surely your rings have seated in 300 miles.
Cruiser
Joined: Dec 2010
Posts: 102
Likes: 1
From: Canada
There are a number of different testers, but they all work about the same..It measures the amount of compressed air that can be held in the cylinder, without leaking out..it gives a much better idea of ring seal and valve condition than a compression tester
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Novice
Joined: Mar 2010
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From: usa
I'm fine with just the compression test I did. I repeated it about 3 times with the same results. It is where it should be for my elevation. No need to do any more test.
Thanks for all the info.
Thanks for all the info.
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HDF Community Team
Joined: Jun 2006
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From: san antonio
I have about 300 miles on a 95 inch build I did. I put in SE 95 inch flat tops, Andrews 54 cam, SE Performance heads. Big boy calculator for this setup at 5200 feet (my elevation) says 155 PSI. My readings were 155 front & 150 rear. So it seems about right.
However when I first did the test I thought I was supposed to be somewhere around 190 because I forgot to input the right elevation. So I redid the test with a little added engine oil in each cylinder. My readings were 175 front & 170 rear. Does that mean my rings are not seated yet? Again I have about 300 miles on the build and the test actually came out right according to the calculator but the added PSI after oil was added worries me a bit.
However when I first did the test I thought I was supposed to be somewhere around 190 because I forgot to input the right elevation. So I redid the test with a little added engine oil in each cylinder. My readings were 175 front & 170 rear. Does that mean my rings are not seated yet? Again I have about 300 miles on the build and the test actually came out right according to the calculator but the added PSI after oil was added worries me a bit.
In any event, at 300 miles the rings should seated; that should have happened in the first 50 miles if broken in properly. Actually, the compression test should be done on a "hot" engine to get a true reading. Additionally, in a new build, there shouldn't be a variance of 20psi in a "dry" and "wet" reading; that's 13.3%. If there was any mileage between tests, part of the difference in the readings could be that the rings were not seated when you took the 155 readings and one of two things is the cause for the later and higher readings. Either the rings have not seated and the oil sealed the rings producing higer readings, or, the rings seated between the first and second set of readings plus the additional sealing provided by the oil.
Normally, oil would be added to a cylinder that had a low reading to see if the low reading was the result of worn rings or a leaking valve. A cyliner reading 135 when the other reads 155 warrants further testing. Add oil to temporarily seal the rings and if the reading jumps up, rings are worn, if the reading stays the same, leaky valve.
For peace of mind, measure again when the engine is hot and if you are reading above 165, forget about it. It is a good practice to take compression readings early in the life of a new build so you have a baseline to check against in the future. Write the "hot" readings down so you don't lose them for future refernce.
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Road Warrior
Joined: Apr 2014
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From: Squamish, B.C.
If your dry test was 40psi and the wet test was 120psi that suggests your rings are leaking bad!!
Your dry test shouldn't drop below 90 psi.
All adding the oil did was tell you it's the rings not the valves.
Your dry test shouldn't drop below 90 psi.
All adding the oil did was tell you it's the rings not the valves.
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Joined: Oct 2019
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From: OH
If your post is 10 years after the first post your CPU is leaking bad !
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