Compression Test Results, what do you think?

[Lynx331]

I finnaly did a Compression test on my 87 GT. The car has 132,000 Miles on it. Heres a picture with the results for each cylinder? Is this good?

 

[tomst9]

i would say thats pretty good. They are all within 20% of eachother.
tom

 

[90mustangGT]

1-6 look real good, 170-182psi, but 7-8 at only 100, that's way more than good. Your engine is alive, you only need 70psi for combustion but your really getting close. Put a teaspoon of oil in the cylinder and test those two again and see if the number changes much, if it does that probally means it the rings, otherwise check to see if you have a valve related or gasket related problem.

 

[HISSIN50]

all 8 look awesome - 12 psi difference from high to low is great.

what Jason is referring to in his post is the wet test i talked about in your other thread on doing compression tests. i would bet all the cylinders would go up very similar amounts with your numbers (if you had a low cylinder, the wet test helps isolate where the leak is).

 

[Michael Yount]

90 Mustang - I think you read the data incorrectly. All between 170 and 182 - 7% spread; and most of them between 175 and 180. Looks awesome.

 

[TrickStang37]

never seen a real tight motor with good compression #'s make more power than a motor with lower #'s. as stated above, as long as their within about 20% theyre fine.

 

[Lynx331]

kewl, thanks guys

 

[87'GTstang]

never seen a real tight motor with good compression #'s make more power than a motor with lower #'s. as stated above, as long as their within about 20% theyre fine.

The higher the compression, then the more the "power" from the combustion is efficient had stays in the combustion chamber percentage wise. By definiton the tighter the engine then the higher the compression numbers should be. By all means, the better the compression then the more power the engine will produce. Each engine has a given minimum compression needed to turn over so it will vary. I believe the 5.0 and many others is at 100 psi, so yes, those numbers are very good!

 

[Michael Yount]

Not to take the thread in a different direction - but you have to be careful not to read too much into cranking compression numbers. While they do provide a relative snap-shot of how things are between the cylinders, the type of cam in the car makes a HUGE difference on the cranking compression numbers. The more overlap, the less psi on a crank-test. While static compression ratio impacts the numbers, two engines with equally well-sealing and integrous bottom ends can end up with drastically different cranking compression numbers based on different static CR and camshaft overlap. In fact the one with less CR and a milder cam can have HIGHER numbers than the one with more CR and a cam with more overlap. So don't run too far too fast with what those numbers mean.