I'm removing the engine out of my car to do some work under the hood and decided to do a compression test on it first. My mechanic wanted me to post the results on here to see what you guys think of it.

1- 175
2- 189
3- 190
4- 182
5- 170
6- 180
7- 186
8- 172

Is that not too bad or what???

 

That's reasonable, it's about what one of those motors should do.

Nothing spectacular of course, but it indicates that the cylinders all seal pretty well, no obvious major malfunctions there.

The actual raw numbers from a compression test are mostly meaningless, except as a ballpark sort of thing. The process you're measuring is adiabatic, which means that all the heat in the gas is contained (for all practical purposes) during the course of the test. That is, when compressed, the gas in the cyl heats up, which increases the pressure beyond just the static CR times atmospheric. If you could somehow pressurize a cylinder and then wait for it to cool back down to its original temp, you could calculate the compression ratio from those numbers; but that's plainly not possible.

Also, other things affect those numbers, above all the cam profile. The smaller a cam the motor has, the higher the numbers will be, because cams that are optimized for higher-RPM operation open the valves for longer, which allows more compression to bleed off at the beginning of the intake stroke.

To evaluate a motor's condition, you look for consistency among cylinders, and for the absolute number to be appropriate to the motor's known parts; yours fit both of those fairly well. If a cylinder or 2 were defective in some way, their number would be way higher or way lower than others, so as long as they're all within 10% or so, it's an indication of good health.

 

That's not too bad for a cranking compression pressure.

You don't have any adjacent cylinders that are on the high or low ends of the range. None of the cylinders are more than 5% off the median pressure. That should be good for a stock engine.

EDIT: Damn! Beaten to the punch again. I gotta take a keyboarding course...

 

Better than the 65-80psi i got from my 305... all i have to say, lol.

 

Here's a basic one: What's the right way to do a compression test? I think I have a blown head gasket, but I want to be sure before I tear everything apart.

What's the right procedure to do this?

 

all plugs out and throttle plate open

 

And, do I just disconnect the ignition coil wire and turn the starter over a couple times?

 

coil doesn't really matter one way or the other, yeah you'd have to crank the engine over a few times, 4 or so, to make it work