Question of compression

[Subliminal]

Hey guys, I think I know the answer to this, but I'm going to pose it anyway:

I checked compression on my new car yesterday and here's what I got:

120, 90, 90, 120

Any ideas why it would be so consistant on the cylinders that fire together?

Incidentally, the car is really torquey down low and misses a little bit up top.

I haven't had a chance to check cam timing yet, but that's what I'm thinking it is. Think that could cause the compression phenomenon?

Thanks!

[altered7151]

You might also possibly have lifted the gasket a little bit between those two cylinders, not much, but just enough to leak some pressure when you do the compression test. Did you try a leak-down?

[Subliminal]

Nope. Just bought the car this past weekend, and have been spending every day doing a little work on it.

Of course, every day consists of the hours of daylight when i'm not at work, which is about 4:20 to 5:00.

Could timing do that to compression, though?

[GLHSKEN]

Very possible,

Any blow bye??

[Frank]

What is the leak down rate? Then what happens with a little oil? It can tell you if you have issues with anything other then the rings.

[Subliminal]

Honestly, I don't even know how to do a leakdown test. There's no blowby that i know of yet. Like I said, it's pretty new to me.

[turbovanman²]

2 cylinders side by side, 99% sure you've got a blown head gasket. If you have little blowby, that confirms it.

To use a leakdown test is simple, you put the cylinder your using at TDC, make sure the valves are closed, hook up tester and turn the pressure knob to 100psi, you need an aircompressor, the other guage will show a number, its also a 100 psi guage. Now if that guage reads 50 psi, you have 50% leakdown, and if it reads 98% like mine does, you have 2% leakdown. NOw if its really bad, you can listen at the exhaust pipe or air filter or a loud hissing indicating a leaking valve.

[pooky]

2 cylinders side by side, 99% sure you've got a blown head gasket. If you have little blowby, that confirms it.

To use a leakdown test is simple, you put the cylinder your using at TDC, make sure the valves are closed, hook up tester and turn the pressure knob to 100psi, you need an aircompressor, the other guage will show a number, its also a 100 psi guage. Now if that guage reads 50 psi, you have 50% leakdown, and if it reads 98% like mine does, you have 2% leakdown. NOw if its really bad, you can listen at the exhaust pipe or air filter or a loud hissing indicating a leaking valve.

AKA a pressure differential test. Even better than a compression test in my opinion.

[turbovanman²]

AKA a pressure differential test. Even better than a compression test in my opinion.

Please explain?

[Una]

I'd say the cam is off a tooth or two.. A blown headgasket would have far lower compression.

[mo' parts]

those numbers look kind of familiar.
mine was 135 90 90 135, both 2&3 had hairline cracks. hopefully you have the head gasket prob. though.......

[Subliminal]

Hairline cracks? In the head?

That would be relatively easy, as I have 4 heads sitting on a shelf right now.

[mo' parts]

Hairline cracks? In the head?

That would be relatively easy, as I have 4 heads sitting on a shelf right now.

sorry, lol

in the pistons
it had a very small amount of blo-by.

[Subliminal]

Oh, roger that.

Actually, i have a whole set of t2 rods and new fed mogul pistons with hasting rings sitting on my workbench, so that wouldn't be the end of the world either.

Although, i have to admit, I don't relish ripping into this thing any more than necessary at this point.

d

[Subliminal]

Oh, and thanks for the help,guys!

[turbovanman²]

Have you got the head off yet, if not hurry the hell up,

[Subliminal]

Naw, no need right now. Too much other stuff going on. I'll drive her into the ground if i have to. Between my wife, my job, my family, and a premature case of arthritis, i'm all booked up over the next couple of weeks.