pieball

Brought my car(75k mi.) into the shop today for some fixes and got a compression test done to see where my engine stood before I go for a major power upgrade. I didn't have time for a leak down test as I added a couple of other fixes to a list. There are no oil consumption/power problems. Engine was warm and throttle open. Numbers were 120,135,140,130. Wasn't very pleased, but my tech said not to worry as there were no "issues". I did opt for one of those detergent runs to maybe loose some carbon on valves if there was any, but I won't know if it helped until another full comp./leak test.

Zero10

The 120 worries me, other than that, they seem alright. 130+ are good numbers. You may already know, but all of the numbers should be within 10% of each other.

Ian Carr

Should do the oil test. When doing compreshion (your 120) squirt a little oil into the cylinder through the sparkplug hole then do a compreshion test again if the numbers go up to 130+ its a good sign that your rings are gone. If the numbers stay the same its could be the head gasket or some thing less bad than rings going/gone.

In my case my numbers where 130,135,115,125... Turns out that the rings were gone and scored the cylinder wall pretty bad in cylinders 3 and 4...

-Ian

pieball

Yeah, that's what I thought as well. That's why I chose a cheap detergent fix! Hopefully it'll pay off like gangbusters! I'll keep my fingers crossed.

ehall

Here's a related question. I had a pt done, and though all were about the same, they were all in the 120.'s, and the tech said there were no issues. SO, how bad IS bad?

pieball

Thanks guys. So I guess I'll redo the plain comp. test to see if the detergent is worth a ****, then drop some oil in that low cylinder. Follow that up with a leak down test and then what? Say I get that low cyl. up, am I just fine if I can get all 130+? If not, how long should/can I wait, especially if there are no other issues if that cyl. doesn't rise?

azmi951

i did mine a while ago and it was in the 120PSI range. My car ran and still runs really well.

Zero10

The compression numbers themselves mean less than the difference between them. The numbers themselves depend on a couple of things, temperature, altitude, etc. Remember, only add a little oil to the cylinder. Otherwise you will get very high numbers, did that on my N/A, numbers looked amazing for one compression test, until the oil drained past the rings.

Numbers in the 120psi range are okay. What's the mileage on the car?
Ideally, I believe they should be around 150psi, but IMO, over 110psi is good enough. Below 110psi and it needs to be rebuilt badly. 130+psi are great numbers for a used engine. 120psi is still doing decent.
Just for s***'s and giggles, the compression numbers on my 86 NA are 95, 97, 99, 96.

awilson40

Mine is at 150- 155 across the board.
You need to check fully warm and with throttle held open during the test.
It really makes a diff as these engines expand a lot when warmed up.
Kind of like the SR-71