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.

 

I’m certainly no expert on your question, but it seems reasonable to me that adding a little oil will always give you a little higher compression reading. You’re showing about a 13% increase in pressure, which does seem a little higher than what I would have expected. Hopefully someone with first-hand experience will jump in.

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.

 

a wet test will almost always give a higher compression reading..Make sure you have the throttle wide open and a well charged battery, or you will get a low reading

 

That's what I was thinking I just wanted to double check.
Thanks

 

How you done a leak down test?

 

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

 

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.

 

Assuming that chamber volume of the SE heads is 76cc, deck height is 0.00" and head gasket thickness is .030", my calcs show static CR should be 165.5. I doubt that the chamber volume is 76ccs and a also doubt deck height is 0.00" which leaves some wiggle room in the numbers. There can also be the accuracy of the guage if the guage is one of the less expensive units. I have seen significant differences in measurement accuracy that seems to correspond to how much the guage cost.

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.

 

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.

 

If your post is 10 years after the first post your CPU is leaking bad !