Cams and Compression

[STAATS]

I know a healthy stock S54 should be 160-175psi compression per cylinder (with spread tolerance) but given the VANOS shouldn't do anything when doing a compression test I can only imagine that the static compression of cammed engines is lower. Assuming stock CR build does anyone know the target / healthy range compression numbers for the various sets of Schrick cams? Ie 280/272, 288/280 etc... specifically I am interested in the 280/272 but figured I'd open the floor in the topic it all...

[maupineda]

The spec per ISTA+ says 12 to 14 bar, which is 168 to 196. A bit of a large range, but maybe that is dependant on what temp the engine is and the position of the rings at the time of measure, so I understand why the wide range.

If the aftermarket cams affect the overlap much then yes, the compression reading may go lower, you would need the datasheet of both cams to do some analysis. Your question is very interesting indeed, I hope someone knows based on the engineering spec of the listed cams.

[STAATS]

Yer I am surprised I couldn't find anything within the E46 M3 community after scouring the internet. There is many articles on how cams impact compression but in our community the only comp numbers I can find seem to be stock numbers. Cams for this engine have become and extremely standard mod in this community in the last 10yrs so it's interesting that this topic hasn't come out sooner.

[STAATS]

Here is some background theory that has prompted me to start asking the question based on the experience I am having:

https://www.crankshaftcoalition.com/wiki/Cam_and_compression_ratio_compatibility

Now obviously we have variable valve timing (VANOS) so it gets a tad more complicated and that why we can have smooth idle and still get power up high BUT I think think that when the spark plugs and fuel pump are disconnected the VANOS won't act and as a result shouldn't change a compression test so hotter cams should drop compression test figures... I am just not sure by how much and/or if all my above VANOS assumptions are correct... hence its hard for me to glean any practical take home from the theory linked other than I need more knowledge.

[digger]

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

[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

[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]

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.

[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]

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.

[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 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

[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

[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

[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)