Compression test confusion! Really good numbers or innacurate test?

[SilviaSalvia]

I bought a SR20DET redtop from jdm engine depot about a month ago. Warranty is up in a couple days so I want to be sure the engine is good before that comes up.

Put a little bit of oil in each cylinder to keep the pistons from dry rubbing against the walls since the engine has been sitting for such a long time before it even got to the U.S. Tried compression test when I got it but starter went bad so I finally got a new one. 1 month later I try the compression test again. Didn't add any oil this time.

1st (Farthest away from transmission) - 150
2nd- 150
3rd- 150
4th - 165

I looked up a bunch of compression tests and I can't figure out if this is good or not. Should be even across the board if its nice and healthy but why the hell is the last one 15 higher? Is that a good thing?

BTW if this wasn't obvious already, this is a completely cold as cold can be compression test. Apparently once the engine is warm, the numbers should shoot up about 10psi(?)

ALSO to note, I've been using an old battery that's been sitting around from when I had my single cam. Not sure if that effects anything.

Not done with the throttle open.

Each cylinder got a good amount of cranks before I stopped.

[Kallixtos]

That's not bad on a cold engine. You can also add a small amount of oil to each of the cylinders, like you did before, your numbers should rise a bit.

[SharkMan]

Fsm states a reading should be Standard @ 156psi and a Minimal of 128psi and a variance limit of(difference limit between cylinders) of 14psi.

Note: this is from the s14 fsm. And hscalixto is right about the oil(also stated in the fsm).

[SilviaSalvia]

I understand but was the compression test done right? I think its a bit odd for 150 150 150 165. Although its at the maximum of acceptable difference its still a bit odd. Shouldnt it be lower than the rest if anything?

Maybe it wasn't top dead center?

[zombiewolf513]

Being at TDC has nothing to do with it.

-bring engine to operating temp
-unplug CAS
-hold throttle open while cranking with compression tester
-take video of each cylinder for playback

[Pirate_Freder]

TDC doesn't matter BUT WOT does. And in terms of doing it wrong,all u do is pull the fuel pump fuse/crank to clear fuel, remove all spark plugs, securely install the compression tester and crank for several turns at of the engine at WOT. Plus, as mentioned before, if a cylinder tests low you can add a cap full of oil through the plug hole and if there is significant improvement then the rings may be worn. As for your high cylinder, if you know which plug goes where you can check for carbon build up; if present there may be severe build up on the piston consequently raising the compression ratio.

Sent from my SAMSUNG-SGH-I717 using Tapatalk 2

[zombiewolf513]

Ive never heard of relieving fuel pressure for a compression test. Not saying its wrong, but just unplugging the cas connector should keep plugs and injectors from firing

[SharkMan]

I understand but was the compression test done right? I think its a bit odd for 150 150 150 165. Although its at the maximum of acceptable difference its still a bit odd. Shouldnt it be lower than the rest if anything?

Maybe it wasn't top dead center?

As stated above tdc, has nothing to do with it. And cylinders even though they are on the same engine aren't going to wear at the same pace necessarily(they are each their own sealed compartment with many variables effecting them). Hence why you have an allowance between them.

Personally I say you should be fine, but as already suggested I would add a little oil and recheck to see if the numbers get closer or further apart.

[fliprayzin240sx]

Thats not bad, I've had an S13 tester test up to 180 psi. Carbon build up can cause it to bump up some.

[SilviaSalvia]

Okay thanks I'm going to try with a lil oil in each cylinder. Btw engine is not connected to anything. Its on an engine stand.