Cams and Compression

[STAATS]

Checkout the updated video, in the first video readings were low because of crappy gauge, here’s updated video with good quality gauge. Totally different results, it’s essential to have a good test gauge, same car same setup

https://youtu.be/CDr-fXP0NJM

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Yer I have a feeling it was the gauge I was using - so I think after I have done some other jobs on my car I might invest in a better gauge and maybe a leak down kit as well instead of borrowing and then go from there. I have put it on the back burner somewhat as it is a newish rebuild by Andrew Lang so i think its more likely reading error than an actual issue as in every other way its in good health and even if the readings are correct I am not actually going to do anything about it until its time for a new rebuild so a long way off... hence getting a new gauge or leak down testing is on the list, but below other jobs like finally getting a helmet and taking this thing to the track haha

[duracellttu]

Here is the OTC brand I used for my compression test and leak down test, which can be found in Amazon. I should note that Lang built my head and performed a leak down test with the exact l same brand gauge at his shop.

[DoubleSidedTape]

I have Schrick 288/280, 320is coated followers, and Megan headers. Everything else stock. Just did a compression test on a cold engine with a harbor freight gauge. Here's what I got:

Cyl 1: 90 psi
Cyl 2: 95 psi
Cyl 3: 90 psi
Cyl 4: 95 psi
Cyl 5: 95 psi
Cyl 6: 95 psi


The car has been sitting for a week since the weekend before last when I took a 600 mile road trip where it drove great. I had it on the Dyno a couple weeks ago and it seemed to make great numbers, although I have no baseline to compare to.

Should I be worried? I am getting multiple misfires so I have a set of coils on order (I have Eldor coils purchased for my previous m3 3 years ago). Plugs are new, along with o2 sensors and TPS.

[zzyzx85]

I have Schrick 288/280, 320is coated followers, and Megan headers. Everything else stock. Just did a compression test on a cold engine with a harbor freight gauge. Here's what I got:

Cyl 1: 90 psi
Cyl 2: 95 psi
Cyl 3: 90 psi
Cyl 4: 95 psi
Cyl 5: 95 psi
Cyl 6: 95 psi


The car has been sitting for a week since the weekend before last when I took a 600 mile road trip where it drove great. I had it on the Dyno a couple weeks ago and it seemed to make great numbers, although I have no baseline to compare to.

Should I be worried? I am getting multiple misfires so I have a set of coils on order (I have Eldor coils purchased for my previous m3 3 years ago). Plugs are new, along with o2 sensors and TPS.

A compression test should be done when the engine is brought up to operating temperature, so the "low" numbers are probably from that.

Is it misfiring under load? I've heard of some engines misfiring in sequence where the first cylinder's misfire threw off the rest of them.

[DoubleSidedTape]

A compression test should be done when the engine is brought up to operating temperature, so the "low" numbers are probably from that.

Is it misfiring under load? I've heard of some engines misfiring in sequence where the first cylinder's misfire threw off the rest of them.

Under load seems ok. That dyno plot is from about 3 weeks ago and I had no issues there, but I get those codes for "Misfire, Cyl N without cutout" on 3-5 cylinders and "Misfire, multiple cylinders without cutout" pretty consistently.

I drove around to get the oil up to temp to do an oil change and re-tested cylinder 1, and it showed 105 psi with that gauge. I don't know if it was the gauge or my technique or whatever, I think if my compression was that bad on all cylinders I would notice it on the dyno and the butt dyno, so I think I'm probably good to just drive it this summer and then pull the head over the winter.