Are these good compression numbers?

[Lee in Ottawa]

Hey guys had a compression and leakdown tests done on my 535i because I don't want to turbo it if it's no good.

Are these numbers good?

Cyl1 165
cyl2 135
cyl3 135
cyl4 145
cyl5 150
cyl6 135

And for the leakdown the mech wrote

cly 1-4 read 29/30 5-6 28/30

What does all this mean. Is she healthy enough to handle a few pounds of boost?

[Dave M]

OK, I'll bite.

I'm no leak down interpreter, but if those numbers are % leakage, I would think........not so good. The compression numbers are well outside the bmw limits as well.

I think the extra boost would find ample room to make a quick escape;)

Did the mech provide any feedback, or just the numbers. Your money should be worth more than just a bunch of numbers.

Anyhow, someone else tell me I'm wrong.

Dave M

[Lee in Ottawa]

Well i brought the car to a new mech this time. One of my buddy's friends. Problem was that he is a honda mech however his old car was a 95 525i. Anyways he told me the motor was in fairly good shape and should have no problem handling boost. He said for the leakdown that for the 30psi he put in it held 29/28psi. So lost 1-2 psi. He said 5% air escaping is acceptable. I was hoping someone here would have some numbers to compare too

[Dave M]

Ahh, that makes more sense on the leakdown and 5% seems reasonable, assuming the test was done correctly. Someone who knows leakdown tolerances better will provide better feedback.

I would, however, be concerned with the comp #s. I believe 7psi is the 'in spec'limit for these engines (or is it 7%). Either way, you're well above it.

Did you also try a wet test (dump a teaspoon of oil into each cylinder and see if the comp rises)? This may indicate lower end (rings) issues.

Did you have the throttle open all the way during the test?

How many cranks to max comp?

Was it the same # of cranks for each cylinder?

Are you going through oil between changes?

What do your plugs look like in the low comp cylinders?

My 525im ran 'fine' with a bum #5 cylinder. I didn't realize how pooched it was until I did some investigating (120 psi)

I hope yours is better than it sounds.

Get us some info and we'll be glad to help

Later,

Dave M

[Lee in Ottawa]

Umm I don't have answers to most of your questions but i'll get them. I am going through oil in between oil changes but i know im losing it at the oil pan (next weeks project) HE said my plugs looked okay but that he could tell it was running a little rich but they were all consistant.
What is spec for these engines?

[Bill R.]

accurate leakdown testers that i've seen use 100psi and virtually every orifice i've seen was calibrated for flow with 100psi. I wouldn't trust the results with 30psi on the leaddown test. Also many of the questions asked below do apply, such as wet and dry compression test and was the throttle plate held wide open ? and was the afm taken out of the circuit while the test was done?



Well i brought the car to a new mech this time. One of my buddy's friends. Problem was that he is a honda mech however his old car was a 95 525i. Anyways he told me the motor was in fairly good shape and should have no problem handling boost. He said for the leakdown that for the 30psi he put in it held 29/28psi. So lost 1-2 psi. He said 5% air escaping is acceptable. I was hoping someone here would have some numbers to compare too

[Dave M]

Bentley states 142-156 minimum PSI. 7 PSI max difference between cylinders. Different compresion testers may deliver different results. The max PSI is less important than the consistency (as long as we're talking a reasonable max such as your 165).

Dave M