Engine Compression
 

I did a tune up and decide to perform a engine compresion test. What do you guys think of the results? Is it okay for a 1990 5.0 LX coupe with 120,000 mile engine? Has anyone done this test and whats your results?

Cylinder 1= 150
Cylinder 2= 145
Cylinder 3= 145
Cylinder 4= 145
Cylinder 5= 150
Cylinder 6= 155
Cylinder 7= 150
Cylinder 8= 155

If I did the math right, your lowest cylinders (145) are 93.5% of the highest (155) cylinders, I don't know exactly how to interpret that, though I believe that the dogma is that for a performance engine it should be no more than the high 90's, 75 percent for your average car. From my low wisdom, I would say you are pretty good.

Your numbers are real close to what mine was when I checked the stock engine in my 89 last summer(100k miles). I did have one cylinder that was 160 though. From what I remember, they are supposed to be within 10% of each other.. looks like your ok.

10 % of from best to worst is correct.

Since this this post is about compression.

If you get a real low cylinder,say 100lbs, try this.

Squirt some oil into the cylinder and crank it over. If the compression goes up your rings are worn. If nothing changes, your valve/head has the problem.

My .02$