Nicholbry

I'm rather green, so please forgive me for asking a question that most of you may find remedial. Although I've found a couple pages here on Rennlist regarding "Compression Test" and the results of many a member; I've yet to reveal the answer to the question:

What are good compression numbers for the 32V 5.0 liter engine in our 87+ cars and what would be considered unfavorable? I suppose I'm looking for a range or scale of numbers; for example, best - good - avg. - poor - bad

Thanks,

JHowell37

180ish I think.

Hilton

Sounds like you're making progress - good to see an update

Based on the numbers i've seen discussed, 180 as suggested above is pretty normal, going up to 210 for a good condition, warmed-up engine.

I've seen people concerned about less than 150, but there's a lot of variables (how warm, whether there's oil in the cylinder, valve timing) that can affect, and the advice seems to usually be to check that compression is consistent across all cylinders (within 15%).

Of course, I'm not an expert, but I do read a lot of advice from people who know more than me

A search for "compression test results" will probably yield more meaningful advice.

Mike Frye

I agree with what Hilton said, except I think the +-15% is a bit much.

If the rest are about 180psi, 15% would be from 153-207.

10% would be a range from 162-198, which still seems like a lot.

I think I'd be more comfortable in the +/- 5-7% variation range. If one or two cylinders are much lower than the rest, you may have a problem.

Mine's an '85, but here were my numbers from last year:

cyl1 165 cyl5 155
2 158 6 155
3 157 7 165
4 156 8 170

SwayBar

All of your cylinders should be above 180 psi; if they are, then you are in good shape.

heinrich

One of mine tested consistently 180-182 on all cylinders. Made 299 at the wheels stock.

Mike Frye

I guess mine were no good. Have to test them warm again this week. Hope they're better.

SwayBar

We ran into a similar problem with an engine last weekend. Cold it did 150 psi, but after running the engine, that cylinder did 180+ like the rest. Needless to say, the owner was greatly relieved afterward.

Mike Frye

Thanks, I don't remember if it was cold or warm last year, but I know it was when I just got it and before most of the work I did and hardly any driving (for who knows how long). Now I think I'll get a more accurate set of numbers, whether or not they're better remains to be seen. I looked around and asked when I first posted these, and no one said anything that concerned me or I would have rechecked. On that particular thread, I'm pretty sure the only concern was consistency across the cylinders, not so much a threshold number. Now I hear 180 is the magic number. You live and learn.

Car runs great and pulls like a monster right now. If there's something wrong I can't feel it.

AO

When i did mine a couple years back I use a HF tester and got readings 155~165. We used a better quality tool and got 180's, so the tool make a HUGE difference too. I'd be mostly concerned with even numbers.

glork98

This is my experience also. The gauges and the adaptors used result in different readings. Even numbers indicate health as the cylinders will not fail evenly. Within 5 psi excellent. 10 psi good. 15 psi marginal. 20+ psi and it's time for a rebuild.

Mike Frye

Thanks Andrew, that may be the biggest factor, I'll try it warmed up with my cheapo compression test kit and if it still comes up low, I'll check into some better stuff. I wouldn't have thought of that for something this seemingly simple.

Sorry for the hijack.

Lizard928

As well when doing a compression test you should hold the engine at WOT.

two reasons you arent then choking the car for air, so it will reach max compression numbers quicker, and second reason is most vehicles have a flood clear at 70+% throttle, meaning you arent dumping raw fuel into the cylinders to wash the oil off the walls.

And mike when I did the compression test on my 86 engine I got basically 210 across the board.

Mike Frye

Well la-dee-da for you.

At almost 210k miles, I'm just happy every time it cranks over when I turn the key.

Lizard928

that is with over 300k Km on the engine. so I am not far behind your 210.