My question is how much psi does a cylinder need to see in order to give an accurate reading of leakage? The reason I ask is because I bought a new tester that operates on 28 psi. At that pressure my cylinders are under 10%. But if I skip the tester and put 100 psi to it, it sounds like the rings aren’t even there.

The test pressure won't change the percent of leakage, both the test pressure and leakage are directly proportional.

Don't go nuts looking at the leak numbers, they can mean nothing!, Look for consistency from cylinder to cylinder.

I have seen leak percentages 5% on one cylinder and 40% on the one next to it and both have a cranking compression of 200 psi and engine ran just fine. I dont put alot of value into leak numbers unless its 100% lol

quote:

Originally posted by Big Steve:
I have seen leak percentages 5% on one cylinder and 40% on the one next to it and both have a cranking compression of 200 psi and engine ran just fine. I dont put alot of value into leak numbers unless its 100% lol

I just use it as a valve to blow air so I can listen to where the hole is this time. LOL.

That sounds like too much experience Bucky

80 psi minimum 100 max

They either leak less than 5%, or they get rebuilt here.

If they leak test good initially, they'll stay that way for 100's of laps.

quote:

Originally posted by vetman:
That sounds like too much experience Bucky

I learn best when the lessons are spendy and cause a bunch of work

Dykes or conventional ring set?

Bob

Conventional

I agree with Al, look for consistent numbers, and you should get them with a conventional ring set.

Bob

Leakdown Testers are not all the same. Some have an odd sized orifice and readings can give poor readings. Take it apart and measure yours. Beside poor piston/cylinder seal and power loss or oil in the combustion area, a leak down test is only of high value to find a low cylinders. I found in race engines, oil in the roof of the exhaust ports and header to be a better better gauge of seal. This can lead to detonation in methanol hi compression engines.
FAA has good details on the size of that orifice
https://en.wikipedia.org/wiki/Leak-down_tester