Compression Testing Questions

[Denny]

I've been able to do four cylinders so far, 1 and 4-6, but 2 and 3 are hard to get to, any trick to get to them without taking off the intake manifold? If I take off the manifold, do I need to have it back on to do the compression test or will I be ok, it won't fudge the results? And what are healthy numbers? Two cylinders made 240psi and the other two made 235, I saw an Ebay auction for a 3.2 where the seller said it made 200psi on a test, so I assume my reading so far are good?
Thanks in advance

 

[noSHO]

Those are HIGH numbers Denny. Like as in the compression a SHO Shop bored out 3.0L with the higher compression pistons makes. Your car is only putting down 125 fwhp? Did you and Chris take care of that yet? I thought I read something elsewhere about you getting a new y-pipe... Standard compression values are in the range of 190-210. They can really vary but that's what is most typical.

 

[naval-avi8or]

The lowest needs to be at least 75% of the highest. You don't have to have the intake manifold on for the test.

 

[Denny]

noSHO:
Those are HIGH numbers Denny. Like as in the compression a SHO Shop bored out 3.0L with the higher compression pistons makes. Your car is only putting down 125 fwhp? Did you and Chris take care of that yet? I thought I read something elsewhere about you getting a new y-pipe... Standard compression values are in the range of 190-210. They can really vary but that's what is most typical.

eek! WHAT?!?! So my numbers are higher than normal?!? Well this car has a bit over 164K, when we pulled off the valve covers for the 60K, it looked clean. I wonder if sometime in the past 12 years it was played with and some things done and then later on something went wrong, because it's still stalling and we can't find the missing horsepower
But I'm serious, my dad and I got 235-240, so that's really good? Hmm I wonder if somebody shaved the heads or changed the pistons . . ..

 

[clintonk]

My '90's dry compression numbers were between 200 and 240 when I tested them last year. Runs fine.

Clinton Knight
'90 White 182K
'95 Green 52K

 

[Blast7]

Denny:

noSHO
.

eek! WHAT?!?! So my numbers are higher than normal?!? Well this car has a bit over 164K, when we pulled off the valve covers for the 60K, it looked clean. I wonder if sometime in the past 12 years it was played with and some things done and then later on something went wrong, because it's still stalling and we can't find the missing horsepower
But I'm serious, my dad and I got 235-240, so that's really good? Hmm I wonder if somebody shaved the heads or changed the pistons . . ..[/QB]

Could you explain your stalling problem more? I have a stalling problem/power loss and I may have found the problem.

 

[noSHO]

So Denny, your stalling and missing power problem is still there? Or not?

 

[pjtoledo]

About the lack of power, have you put a timing light on it to see how much total advance you get? Did you try disconnecting the exhaust at the y pipe to isolate back pressure? MTX,, did anybody slip some 140 weight gear **** in the tranny? Was the loss of power sudden, or did it come on gradually? You have a cat-less y pipe, I've heard the SHO engine works better with some backpressure, but I wouldn't expect that much of a loss.

Perry Toledo,Ohio

<small>[ May 14, 2002, 09:59 PM: Message edited by: pjtoledo ]</small>

 

[Denny]

Sigh
The power loss has been there since before I got it, good news it that everything that gets done to the car somehow makes it a bit peppier or responsive. It dynoed 125 horse two weekends ago with clogged cats. They're gone now and the responsiveness has picked up tremendously, but it's not all there yet.
Stalling happens when you either floor the gas right off of idle or are just sligtly ******* the gas it stalls out. Or in gear under 2K a couple of times too. That worries me becuase the other day I was getting onto the expressway and I though I'd be ok around 1800rpms but it stalled so there I was coasting without power anything onto the freeway.
When the stalling happens there's like this engine chug, the car will vibrate a bit and there's a knocking noise. I'm thinking it has to be fuel related somehow, but when I checked pressure it was good but it wasn't the same as Olympics pressure readings though, could that be something?

 

[bradman]

Have you replaced the O2 sensors yet?

Sounds like the gage you used for the compression test reads a little high.

 

[Denny]

Not since I've had it, haven't pulled any codes from them, but bad ones won't necessarily throw codes and can cause stalling?

 

[noSHO]

What about a fuel filter? If you think it is fuel related that could be the problem...fuel pump? I promise we will get this figured out one way or another...I want to see it run right. Fuel pressure at idle should be 39+/- 2psi. Also check to see that the pressure holds for at least two minutes after you shut the car off. It could be possible that your pressure is bleeding off too fast, but I'm not sure that is the problem. Just throwing some ideas out there to be tossed around.