Cylinder pressure with lower compression ratio?

[R33E8]

I just preformed a cylinder pressure test today on my KA. I got 120,130,125 ,120(engine was cooled down a bit for the last two).. The engine has Arias pistons (8.8:1 I think) with a .5mm overbore.. The head was decked but without the front cover so it has a pretty bad oil leak around the headgasket.. But anyways, do lower compression pistons lower the cylinder pressure?

[Z33TT]

Yes........

[fliprayzin240sx]

Yes, but that seems lower than it should be. Atleast im using the SR as a reference with 8.5-1 compression pistons. Usually, we'd see 150 ish for compression.

[R33E8]

So should there be about a 7.4% decrease in cylinder pressure? Is the math I used to figure it out correct? ((9.5-8.8)/9.5)*100%=7.3684%... I think my cylinder pressures should be in the 160 range...:-/

[4x4le]

are your rings seated yet?

[R33E8]

Well the previous owner told me the engine was rebuilt around 1000 miles ago.. I assume they are? I guess I'll check it again after another 500 or so miles..

[4x4le]

have you tried that gauge on different engines to see how it reads? I have a gauge that reads low on all engines. Some of them just suck. I just use that gauge to look for consistency.

Try another gauge or try that gauge on different engines, which ever is easier for you.

[R33E8]

I only tried it on my engine.. I'm not too surprised by the low readings.. The head gasket is leaking oil pretty bad since the head wasn't decked fully.. I'll try it again on a few other engines when I rent it again from autozone (free rentals ftw!)

[jamg]

leaky valve?

[R33E8]

The previous owner told me the head was refreshed with oem parts when it got decked.. These suggestions are all possibly since I dont know exactly what was done to the engine.. Kinda sucks since I dont want to take it apart (I'll have to anyways to get the head re-decked..) I'm going to perform a leak down test in a couple days to see how that works out..

[TheWolf]

I'm guessing no one told you compression testers were for intercylinder comparison use only. You can tell nothing about the engine from one other than it seems to have pretty even compression across the board.

Get a leak down tester and a mechanics stethoscope. Pressureize the cylinder and then listed to where the air is escaping. You'll have it diagnosed in no time.