Compression test today. NE1 have their #'s handy?

[mgoods50]

Cyls 1-4, all dead center 190psi.
Cyl 5, 182 dry, 185ish wet
cyl6 190psi

What the heck? Bentley says 156 psi!

Yes, I was using a cheapo harbor freight gauge, and I have no reference points from previous tests, but 22% higher? No wonder my car runs like a scalded cat!

What the heck? Was my deck shaved by the PO?

[EricP]

Relative numbers are all that matter above a certain point afaik, sounds like you're in the clear!

[dano670]

How warm was the engine when you did the test?

[mgoods50]

Relative numbers are all that matter above a certain point afaik, sounds like you're in the clear!

Yeah, that's my school of thought too. Wish I would have done the test a year ago, when I bought the tool- now I'd have results to compare with baseline.

I warmed the car up to the point of the idiot gauge showing middle; my autometer full sweep was showing 170 on water. I figured it was probably a little cool, but I didn't want to risk burning fingers and losing a nut- plus, I have a tremor, carpel tunnel in both hands, and Dr. De Quervain's tenosynovitis. . . I didn't want to push my luck.

Compression higher when cooler, I'd assume? But it couldn't be that much, right?

[dano670]

Compression higher when cooler, I'd assume? But it couldn't be that much, right?

Yeah, but that was very critical in rotary engines, but not as drastic as in a piston powered engine. The uniformity is key, and your numbers are really nice.

[pbonsalb]

Normal is around 200-210. But closely spaced is the most important and yours are all within 10 psi.

[Doriftu]

Compression higher when cooler, I'd assume? But it couldn't be that much, right?

Compression would be lower when cold. At operating temperature, the seals expand and make a tighter seal, bringing compression about 5% higher.

[hc1001]

Compression would be lower when cold. At operating temperature, the seals expand and make a tighter seal, bringing compression about 5% higher.

This is correct.

Also you want to check if each cylinder is within 10% of the lowest and highest readings...

when i had a compression test done, my #'s ranged from 150 to 160's. and also found out my valve cover gasket needs replacing... :shifty

[mgoods50]

Thank you all for acknowledging my #'s- I feel like a proud parent :redspot
150-210 is a wide margin. Bentley states the figures I posted earlier, but does not specifically designate S50. Reference is 6 cylinder engines. I know compression is higher for the S50 vs. M50. . . about 1/2:1 ratio, if memory serves.

At least I have a baseline now.

[Tom R]

The 150 values in the Bentley are a service limit.

As a side note, the other day I measured compression values in my s2000 that i am selling and found them to be 250 hot across all 4 cylinders...pretty amazing stuff.

[gk325is]

The pressure will depend on where you are located as well. A guy in Denver will be very different from me at sea level.

[egebhardt]

I'm at sea level with 20w-50.
180psi in the 96 Techno, across the board.
190psi in the 98 Arctic, across the board.
200psi in the 99 Estoril, across the board.
The 152 per the Bentley is rebuild time, if you ask me.

[Hova]

PSI is relative to elevation.

Mine were between 190-195. I am at sea level.

[I3MW]

Normal is around 200-210. But closely spaced is the most important and yours are all within 10 psi.

This. I don't know why we are talking about 150. The actual number is 210, but anything from 190-210 is considered good. With that said consistency matters much more and elevation effects the raw numbers significantly so numbers need to be judged accordingly.

[brian8smith]

As stated, 150 is the service limit, not the target. Anything below and you've got some major issues and likely need a rebuild of sorts.

[mgoods50]

As stated, 150 is the service limit, not the target. Anything below and you've got some major issues and likely need a rebuild of sorts.

Thanks for that clarification. I did not realize it was an implied meaning; I am not formally trained. Does this apply to specs (generally speaking) across the board in the Bentley?

Also, sorry for the delayed follow up, I lost the thread. I'm a little embarrassed to revel the goofball careless mistake I made after the test. . .

In a real hurry to finish up some misc. things like labeling relays with my latest toy ( a little label machine ), I TRANSPOSED the fuel pump and DME relays. This results in NO IGN, NO FUEL. Frustrated, and running late, I assumed one of the 17 year old relays gave up on me, so I searched my parts bin, then cleaned the contacts, then brought out my diagnostic laptop. . . no good, other than to tell me no communication with DME. Great, I thought. . . If only one variable, I could start to narrow down the culprit. Unfortunately, I had also relocated the ADS port to inside the cabin, so perhaps a wiring issue had developed since my last interrogation of modules. Oh, the pleasures of OCD. . . :eek:

My son started to ask me if I had switched them up, but stopped because he knows how anal I am about things and assumed (incorrectly) I would NEVER make a careless mistake. . .

The first strike against me in my teens' mental list of "Why parents are dumb." :eyecrazy What on Earth will I have to accomplish to erase THAT entry?

[pbonsalb]

As stated, 150 is the service limit, not the target. Anything below and you've got some major issues and likely need a rebuild of sorts.

After installing a double thickness headgasket for a stage 2 turbo kit to drop compression from stock 10.5:1 to just under 9.0:1, the new compression test result is around 150 psi.