Compression. What should it be at?

[5LugFoxFanatic]

What should a decent running 5.0 302 have as a compression rating if you do a leak down test? I have heard 100-150. Is this right? Reason I ask is, mine with 136,000 on it has 70 psi per cylinder, which is bad, so I want to see what a new 5.0 should be at.

 

[jrichker]

Some of the recent posts have numbers ranging from 120-185 PSI. If the compression is low, squirt some oil in the cylinder and do it again – if it comes up, the rings are worn. There should be no more than 10% difference between cylinders. Use a blow down leak test (puts compressed air inside cylinders) on cylinders that have more than 10% difference.

If you have access to an air compressor, you can build your own blow down leak tester.

See http://jrichker.stangnet.com/Mustan...ession_tester/Blow_down_comprssion_tester.htm for more information.

 

[crazypete]

I had the same problem. Test it HOT. The cold number will be WAY off.

150-155 is what I got on a nice, clean motor. It said 110 cold. I second the oil trick.

 

[TheUser]

I had the same problem. Test it HOT. The cold number will be WAY off.

150-155 is what I got on a nice, clean motor. It said 110 cold. I second the oil trick.

70 hot or cold is still way low! I tested my GT when it wouldn't start, only crank, so I had no choice but to do it cold and I came up w/ most of them around 140 I believe.

I did my LX 5.0 stock w/ 145k and came up w/ around 140-150 for every cyclinder and I can't remember if the motor was hot or cold, but I'd guess basically cold since I don't like to work on hot motors; burning myself isn't at the top of my list

 

[Dean85GT]

i got about 123-128 on every piston while the engine was cold. It has 212000km on it. Not bad i guess.