Compression numbers

[DSMxTSi]

Jenni and I did a compression test on the '90 with each cylinder at 120 psi. I know that's somewhat low, but how low is that for this altitude? Eric W mentioned that he was getting 120 in 3 cylinders and 112 in another last year, but his car seems pretty damn strong. So am I correct to assume that 120 is a decent number up here in Denver?? The needle jumped pretty quickly to 120, then didn't move much. So that tells us that the rings are in good shape, but the valves/seals may not be. We had put new NGK plugs in before it was started, and it was ran maybe a total of 5-10 minutes previously, and the new plugs were fouled very black when we took them out for the test. No oil on the plugs, just VERY black. I drove it to work down in Castle Rock yesterday and it used at least 1-1/2 quarts of oil, but probably more like 2 quarts. So I think that the head will get rebuilt sometime soon before we drive it more regularly. It does dump a lot of smoke out the exhaust, but it's hard to determine how much of it is oil and how much is fuel. It does run extremely rich since the VPC and GCC were last set for the midwest. We did cut the fuel down at idle, but didn't do much under throttle/boost since we'll be moving in a week and we'd just have tune it all over again. Coolant is perfect, haven't lost a drop.

We will do another compression test on it once we are moved to Missouri and we'll post the results to see the difference in altitudes. We'll probably do a "before and after" on the ESi and Spyder also, and post those too.

Cody & Jenni

[Van]

Altitude plays a big part in compression readings.

I verified this because I got real tired of hearing people say that 120 was bad compression, hehe. I did compression tests up here and down in Denver on my car in the span of a day.

ie: Up here at 8200ft elev, my #2 cyl was a 115, the same cylinder down in Denver (at 5280ft elev) was 125.
A 10 psi difference. All four cylinders showed between a 5 and 10 psi difference between Denver and up here.

Using an average of my Denver compression test readings Cody, I come up with an average of 123 psi. I still have 1g pistons too.

So 120 psi in Denver is good, my car runs great.

When you get to Missouri you can redo it and report what you get.

[V8SpankR]

My last compression test showed 126-133 so I guess that's not too bad?

[DlandryTSI]

I think when salmi sold the 2litere it had 100 across the board.

--Dave

[tekky]

I dun remember for sure Dave might... my car was 125 or 130 across 1-3 and then 5 less on #4......

[DSMxTSi]

Finally got around to doing another compression test to compare with the numbers from Denver.

Cylinder #1 = 140
#2 = 140
#3 = 150
#4 = 150

Not too bad! :) I'm not positive of the elevation here, but I can find out.
Unfortunately during the drive to warm it up to operating temps the positive battery terminal decided to touch the underside of the hood. It touched long enough to burn a nice little hole on the bottom of the hood, plus the battery light and CEL came on on the dash and the CEL finally went off after a few seconds. It seemed to be fine afterwards though, but I'll be checking electrical crap soon enough to be sure.

Cody

[Van]

Thanks for posting and further confirming this Cody!:D

Now maybe people will quit wasting money on rebuilds just because they see 120 psi compression numbers up here.

You'd be surprised how many people just don't get the whole altitude thing and how it plays a key role in alot of different things, hehe.

[ibspoolin]

When i got my motor back I was pissed, my compression varies from 148-165 accross all cylinders. It's nice to know that altitude plays a large part in that figure. I was expecting numbers closer to the 180's, looks like that's right where I'd be at sea level. I have JE 8.5:1 bored 20 over, nothing special just a decent rebuild, I guess.

[BatmanGSX]

Yup, I was getting 123 across the board with a 40K engine. It worried me a little bit back then but just due to the consistancy I forced myself to believe it was okay. Looks like I was right.

I'm building a new one with 8.5:1 compression. I'll compression test that with the same tester and see what happens for some more comparison.

[Red91GSX]

I just swaped my head and did a compression test.

Note: I am in Missouri

#1 145
#2 160
#3 150
#4 145