compression test

[ozosil]

Hello, my car was getting serviced a few days ago, I decided to get a compression test as well on my 323i to see the health of the engine, i didnt do it when I brought it. It came back as 180psi on all cylinders, the mechanic said that is excellent. What do you guys think? what is the average cylinder compression for a beemer?

[FenderBender]

How many miles are on it?

[ozosil]

115km, which is around 70miles i think

[E36 Phantom]

That's way the hell high. Bentley says 142-156.

[Nline6]

how would a engine raise its compression?? Is that even possible under normal circumstances?

[FenderBender]

115km, which is around 70miles i think

Wait, it's brand new? It damn well should have good compression.

[E36 Phantom]

Not really. Lol.

So, could be a few things. There's always operator error & equipment error. Another thing is if the HG had been replaced before, if they used too thin of a gasket, or had to machine the head but still used an OEM gasket instead of a slightly upsized one. Other than that, I'm not really sure off the top of my head.

But, if it's running well, the most important thing is that none of them are significantly below spec, and that none of them vary from each other by more than 5-7psi.

[ozosil]

Well this car must of had alot of tune ups, and it was serviced every 7,000k which is pretty impressive. But anyways it was 180PSI, they might measure it in different standards in the states... but is it a problem if compression is too high?

[ozosil]

Wait, it's brand new? It damn well should have good compression.

hey, thats 70,000 miles, it not brand new lol. The car actually runs very well, i like it because it does not sound like a pop corn machine or a truck, has one of the best e36 idles i heard... BUT FOR HOW LONG!

[FenderBender]

hey, thats 70,000 miles, it not brand new lol. The car actually runs very well, i like it because it does not sound like a pop corn machine or a truck, has one of the best e36 idles i heard... BUT FOR HOW LONG!

Oh, I was wondering lol. You said 70miles up there^

I'm glad to hear it runs so well. Pictures please :thumbup:

[E36 Phantom]

Well this car must of had alot of tune ups, and it was serviced every 7,000k which is pretty impressive. But anyways it was 180PSI, they might measure it in different standards in the states... but is it a problem if compression is too high?

Pounds per Square Inch are Pounds per Square Inch. Don't think there's any other way to measure it.

Honestly, on these motors I don't know if it's a problem or not.

[jason_recliner]

180 is not a problem because there's NO WAY you'd get 180psi unless you've shaved 1/2 an inch off the head, installed round top pistons and have about a 12.5:1 compression ratio.

The reading is clearly erroneous. If they're all reading the same, chances are everything is well.

[Edit:] Compression ratio will be listed in your manual. Mine's 10:1, which puts the typical range about 135-145psi.

[pracklam]

A compression reading of 180 psi is very good for a 70K mile engine. Even better that all cylinders checked out the same. For reference, the compression of a new engine is 200-210 psi. The 142-156 psi cited in a previous post would be the MINIMUM acceptable.

[E36 Phantom]

A compression reading of 180 psi is very good for a 70K mile engine. Even better that all cylinders checked out the same. For reference, the compression of a new engine is 200-210 psi. The 142-156 psi cited in a previous post would be the MINIMUM acceptable.

http://i105.photobucket.com/albums/m237/ChadMKIII/facepalm.jpg

[jason_recliner]

A compression reading of 180 psi is very good for a 70K mile engine. Even better that all cylinders checked out the same. For reference, the compression of a new engine is 200-210 psi. The 142-156 psi cited in a previous post would be the MINIMUM acceptable.

Interesting. That would mean that wherever you live you have an atmosphere of around 21 psi.

The rest of us, back here on Earth, have an atmospheric pressure typically around 14.7 psi.

[ozosil]

but if you do a search it says a health car should have 170+psi in a compression test, i remember my friend showed me how to do a MANUAL compression test on his mazda (by manual I mean taking out the spark plug and plugging in the compression tester thing) and all his cylinders res 200 to 210 psi, so i am sure a car with 150psi was driven like a race car all its life probably

[E36 Phantom]

but if you do a search it says a health car should have 170+psi in a compression test, i remember my friend showed me how to do a MANUAL compression test on his mazda (by manual I mean taking out the spark plug and plugging in the compression tester thing) and all his cylinders res 200 to 210 psi, so i am sure a car with 150psi was driven like a race car all its life probably

Uhm, methinks you should do some more reading then. Compression depends on the motor. It all depends on how it was designed to be. For example, spec for my Jag's AJ-V8 SC engine is the 130's.

Also, I'm not really sure how else you'd test the compression, unless you're just talking about letting the car's computer monitor things.

[jason_recliner]

Actually I may be wrong on this anyway.
I took static pressure and multiplied it by the compression ratio. Seems pretty simple math.
But there could be an additional pressure increase caused by the heat of the compressed air too. If so, that would make higher values possible than the obvious static pressure calculation.

[E36 Phantom]

Jason, you could just list the pressures from the Bentley manual. I'm sure they've already done the math. Lol.

These are 10.5:1, right?