Cams and Compression

[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.

[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]

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.

[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.

[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

Sent from my iPhone using Tapatalk Pro

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]

Hey Everyone,

So I kust saw this thread and figure i would do a compression test, to add to the conversation.

2005 E46 M3 ZCP (203k miles)
Schrick 288/280 cams
Schrick coated followers
Karbonious CSL airbox w/ OEM flap
CSL MAP sensor and air rail
CSL ECU (H-bridge)
SSV1 headers
SSV1 sec 1 (catted)
OEM sec 2
Scorza exhaust
CSL battery (not sure if that matters)

Perform at normal operating engine temp.

C1 - 159
C2 - 159
C3 - 160
C4 - 165
C5 - 157
C6 - 160

Thanks for sharing. This was helpful when comparing my compression numbers today. I'm not as worried as I originally was now that I know aftermarket cams result in lower compress pressures, compared to stock.

2005 E46 M3 ZCP (159k miles)
Schrick 288/280 cams
Schrick coated followers
Karbonious CSL airbox w/ OEM flap
CSL MAP sensor and air rail
CSL ECU (H-bridge)
Ported exhaust on head
SSV1 headers
SSV1 sec 1 (catted)
SS twin pipe (resonate)
SS race exhaust

Perform at normal operating engine temp.

Compression [psi] / Leak Down Loss [%]
C1 - 154 psi / 1%
C2 - 152 psi / 1%
C3 - 152 psi / 3% (crank case)
C4 - 152 psi / 2%
C5 - 148 psi / 2%
C6 - 158 psi / 3% (crank case)

[Radekxpl]

Here, he has your setup, same cams…

https://youtu.be/A-kBFsLRUmQ

so these are now 2 datasets that suggest the more aggressive duration is affecting the reading. Cams affect dynamic compression which is what you are measuring, when the engine is not running both cams are at opposite ends of their adjustment range.

he also read 150, he had a bit more compression but it could be variation on the assembly, the gauge, etc. For comparison purposes I’d say the number are the equivalent.

lately I have used my car for very short drives or just move it in the garage and my oil has also smelled gassy. Just take it for a good drive and check.

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

Sent from my iPhone using Tapatalk Pro

[x Spades x]

Hey Everyone,

So I kust saw this thread and figure i would do a compression test, to add to the conversation.

2005 E46 M3 ZCP (203k miles)
Schrick 288/280 cams
Schrick coated followers
Karbonious CSL airbox w/ OEM flap
CSL MAP sensor and air rail
CSL ECU (H-bridge)
SSV1 headers
SSV1 sec 1 (catted)
OEM sec 2
Scorza exhaust
CSL battery (not sure if that matters)

Perform at normal operating engine temp.

C1 - 159
C2 - 159
C3 - 160
C4 - 165
C5 - 157
C6 - 160

[STAATS]

I saw a ~25psi drop in compression going from factory cams to 288/280. FWIW the dynamic Vanos operation shouldn't affect results much in this circumstance as cams are in "rest" positions (minimum overlap) at idle so when the engine has been run and then shut down they should still be in this position. I check compression on mine a few times a year and it's been quite consistent. These values are at ~80C water/oil temp.

JE 11.5:1 pistons, stock camshafts:
182 - 180 - 181 - 179 - 182 - 184

JE 11.5:1 pistons, Dbilas Dynamic 288/280 cams:
156 - 158 - 155 - 157 - 155 - 157

Leakdown (regulated to 90psi):
1% - 2% - 1% - 1% - 1.5% - 1.5%

Interesting.

I would have been happy if I got mid 150s like you but the mid 140s threw me. I really should do a leakdown test. I have a vague feeling the compression tester I borrowed maybe wasn't the best I think I will invest in one and check it regularly but definately need to look at doing a leak down test as that is probably more important than a straight compression number

[BBRTuning]

I saw a ~25psi drop in compression going from factory cams to 288/280. FWIW the dynamic Vanos operation shouldn't affect results much in this circumstance as cams are in "rest" positions (minimum overlap) at idle so when the engine has been run and then shut down they should still be in this position. I check compression on mine a few times a year and it's been quite consistent. These values are at ~80C water/oil temp.

JE 11.5:1 pistons, stock camshafts:
182 - 180 - 181 - 179 - 182 - 184

JE 11.5:1 pistons, Dbilas Dynamic 288/280 cams:
156 - 158 - 155 - 157 - 155 - 157

Leakdown (regulated to 90psi):
1% - 2% - 1% - 1% - 1.5% - 1.5%

[STAATS]

I tested mine about a year or so before my cam swap, I could test them when I change out plugs just as another datapoint using the same tool just to see what I come up with. Might be a few weeks though, got a few other things on the agenda first that I have to get done.

Yer that would be great - would be one of the best datapoints, same car, same tool, just cam change to truely see the difference. Keep us posted when you get the time to get it done.

[SamGrant951]

I tested mine about a year or so before my cam swap, I could test them when I change out plugs just as another datapoint using the same tool just to see what I come up with. Might be a few weeks though, got a few other things on the agenda first that I have to get done.

[STAATS]

Here, he has your setup, same cams…

https://youtu.be/A-kBFsLRUmQ

so these are now 2 datasets that suggest the more aggressive duration is affecting the reading. Cams affect dynamic compression which is what you are measuring, when the engine is not running both cams are at opposite ends of their adjustment range.

he also read 150, he had a bit more compression but it could be variation on the assembly, the gauge, etc. For comparison purposes I’d say the number are the equivalent.

lately I have used my car for very short drives or just move it in the garage and my oil has also smelled gassy. Just take it for a good drive and check.

Interesting. Thanks for the datapoint.

I am not too worried about the fuel dilution per se... I am 99% comfortable, even before the compression test, that it was just due to cold, short runs. So I am confident it should go away if just drive it properly like I would like haha.

The fuel dilution thing just brought me to compression testing and then the results seemed weird which brought me to this point.

I borrowed a compression tester and it was one of those plug style ones... so I may invest in my own with a threaded attachment and maybe just keep and eye on it at every Inspection 1 or 2 just to see whats up. Along with sticking to the oil analysis at every change interval.

I would still be interested to know what the actual healthy range numbers should be for a cammed S54.

[maupineda]

Here, he has your setup, same cams…

https://youtu.be/A-kBFsLRUmQ

so these are now 2 datasets that suggest the more aggressive duration is affecting the reading. Cams affect dynamic compression which is what you are measuring, when the engine is not running both cams are at opposite ends of their adjustment range.

he also read 150, he had a bit more compression but it could be variation on the assembly, the gauge, etc. For comparison purposes I’d say the number are the equivalent.

lately I have used my car for very short drives or just move it in the garage and my oil has also smelled gassy. Just take it for a good drive and check.

[STAATS]

overlap has almost nothing to do with cranking compression as the engine isnt being fired and is only running at a few hundred rpm , it is the inlet valve closing (IVC which is in degrees after BDC) late that reduces compression. there are some online calculators that will tell you the compression with a cam with IVC 'X' and then you can see what happens if IVC is chnaged to 'Y'

Cams will drop compression all else equal, a 24* duration increase will mean about 12* later IVC (same centreline) which is easily a 20psi or more reduction on a cranking test

i wouldnt worry about cranking compressoin except for diagnostic purposes as the s54 is not a fixed timed engine, so more doesnt mean much

Yer I did figure trying to track a compression number on a variable timed engine was partially a fools errand although BMW themselves set healthy compression readings (although admittedly a large range) and I am outside of that range so wanted to understand what was healthy for aftermarket cams... I tried to look into those calculators and only ended up confusing myself further haha, so much for being an Engineer haha... I'll explain my situation for context as to why I started prodding this topic of enquiry.

I do oil analysis at every oil change. I have done 3 so far. 1 after run-in (~1200mi) all good readings, except mild increased sodium, but likely left over chemicals from build or assembly lube or something as it hasn't appeared in the next 2 tests. 2nd test with 3000kms (~5000kms total on engine) and was all green ticks... finally the current test 3600kms (~8600kms total on engine) has all green ticks for wear metals but raised fuel dilution... For context since the last test I have been forced to drive some shorter runs more frequently as part of my commute.

So anyway this result prompted me to do a Compression Test to check if I had lazy rings or if the fuel dilution is just from short runs and hence my fault and i just need to strecth the cars legs more... so fully expecting healthy compression numbers... Test results (dry) warm engine but not operating temp:

Cyl 1: 144psi
Cyl 2: 140psi
Cyl 3: 146psi
Cyl 4: 145psi
Cyl 5: 148psi
Cyl 6: 140psi

So as you can see the readings are way below the healthy range set by BMW in TIS... the spread is okay, not great but pretty clustered, spread less than 10%. So as a follow-up test to try tease out if it is the rings or something else (without diving into a full leak down test) I did a cheeky wet test, I chose the lowest and highest readings so redid Cyl 2 and Cyl 5 with a teaspoon of oil in the cylinder (let settle, few cranks without tester before taking readings again) and this time both Cylinders go 150psi. So firstly the jump isnt huge and secondly the readings are both the same. To me, without doing a leak down test, this indicates there is no issues with the rings... then it struck me that all the compression readings from BMW and from the community I was comparing to were stock cams so got me looking into cammed engine numbers and then we ended up here...

Its a weird one for me as on face value the compression results are poor yet my oil burn rate is low. I only topped up 500ml on last oil change and that was more just to finish off the bottle in the few weeks leading up to my next oil change, no oil top ups in my previous oil intervals. Also my Dyno numbers after a Paul Claude tune were 310HP at the rear wheels (SSV2 headers and metallic race cats, SS x-pipe resonated Sect 2, SS Sport Muffler, Evolve Airbox and TTFS MAP sensor for CSL tuning, Schrick 280/272 cams) which is a pretty strong result