Exhaust cam timing
 

Hey guys,
I have the option of making an adjustable cam gear for my turbo M111 engine(ex kompressor),the reason i want to make it adjustable is because i believe the timing on the exhaust has been setup to work best with the SC/low exhaust backpressure and may let out a few hp if tweeked .though i have a few questions i need to sort before i decide to go ahead and make it happen.

-Im not sure how far to make it adjustable...somewhere between 4 and 8 degrees sounds logical?.

-Trying to gauge how much valve clearance vs intake valve or vs piston is not the easiest task for me,so once installed i plan to adjust the intake and exhaust gear full advance/retard and turn the engine over by hand while on the engine stand,any thoughts?

-Advancing the exhaust may shorten overlap somewhat which may help the situation with a turbo...though it will also open the exhaust earlier which may not help so there may be minimal gains if any...has anyone here had much experiance with exhaust cam timing?

I managed to score an exhaust sprocket that would be suitable for machining,it has the same timing as my orignial just much more meat around the bolts,im wondering if its worth slotting 6 bolts instead of just the 3,will need to drill the end of the cam flange too accomodate the 6 bolt design but thats no problem however i will need to remove the locating dowel which im not so keen about.

New Gear:
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Original:

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Cheers,
Paul

in basics Paul,
To increase topend u must retard the cams, low end advance. if u apply it to both cams u shift the power up or down the rpm range.

usually a 4 deg on each cam from std point will shift power abt 500rpms up or down, but that means the whole cam profile will shift, so if ur cam has a working range of say 2000 to 5000, it will be 2500 to 5500.

but ur only option is by trial and error i guess. But do test clearances before u run.

Thanks Jay,

Hmm so would that mean cam duration would be the biggest difference in a turbo cam vs a supercharged cam?(rather than timing)

Theres quite a few variables,you could almost say the factory exhaust has a similar backpressure to my turbo setup with free flow exhaust....if this was the case i guess you will simply shift the power up and down the rpm range....however if the backpressure is significantly different from OE on my turbo setup would timing help more than just shift the power band?

As for clearance checks is there an easy way to do this?...surely if i assemble it all and rotate it in the fully advanced/retarded on both ex/in and there is not contact i have a fighting chance?...though if it is close but not touching that could end up being scary at high rpm?

I do believe that your feeling ur engine is running strangled by 6200 rpms and almost dead by 6500. i would assume that case since the stock S/C had an RPM limit which had the engine limited to 5800 redline and ths everything tuned to work with this range.

i cant recall how you are tuning the car, what u need to do is have the intake cam go to zero position at say above 4500 and set some 4 deg of retard in the exhaust cam for starters. then always recalibrate your AFR, then start working on ignition.

as for clearances, 4 degs of advance or retard should be with in the safe range, after all engines usually have that clearance since you can by mistake install the cam gear one tooth off (abt 12deg) and still get away with it.

Thanks Jay,iv had the sprocket machined 5 degrees either way,i will install this weekend and check for interference!...need to make some timing marks on it still.

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cheers,
Paul

I am curious about the exhaust timing also. I have not played with mine yet.
I do want to point out that the intake cam adjuster should be set up to be on through out the rpm range. Mine flows significantly better with it on. I made over 50rwhp with it on vs with it off. The curves were almost identical. I have been playing with it recently and even at 5000rpm I still flow more and make more power with the intake cam advance on. It seems to fade off a little after that but not much difference with it on or off at 6000rpm which is were I shift.
In my opinion I think that Mercedes does everything for low to mid range torque as Jay was saying. So improving high rpm power is the key at a certain point. My car for instance falls on its face at above 5200rpm, which is why I need to do exhaust.

Rebuilt the engine and installed the sprocket this weekend,turned the engine over clockwise and anticlockwise(so the intake cam would advance) with the exhaust cam full advance/retard...didnt appear to be any interferance,so good so far!.

Whipplem,
I agree,but how late to turn off the advance may differ substantially on the kompressor engine,when we first tuned the engine i thought we tuned it with the advance on,but the second time round i found out we hadnt,so we brought it in at 1200rpm and left it on throughout the entire rpm range(which made a huge difference)
Below is a recent dyno vs the stock standard engine a few years back.
Notice how power drops off at around 4300,this is where the cam is normally retarded on the M111,note we have raised the rpm limit to 6300 which helps alot with gear change as the car is still pulling really well at 5800.

So next time we are on the dyno i will retard the intake cam at somewhere around 4200 - 4300 then play with the exhaust cam alittle to see what the outcome is!


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Good to see it put to the test, good luck with this rebuild btw.

Just yesterday we were tuning a 2.3L EVO9 that has variable intake cam and a sprocket on the exhaust cam. The builder had set the exhaust cam by mistake with abt 6deg of advance! Come tuning time we could instantly tell something was off with the cams.

1- Idle vacuum was high
2- Low down pull was amazing (car could pull from a stop with 2 up in 3rd)
3- Power dies after 5800 and logs showed lots of ignition knock despite the low load readings and the mild timing tune.

So we retarded the cam for testing to 4deg of retard, and all the above are now the opposite.
We lost some vacuum, and lost the low down pull as the car cant start in 3rd without frying the clutch now.
Finally power now continues all the way to 7000 and we eliminated the ignition knock.
Intake cam was setup to almost 0 setting in the high range.

Just thought of sharing as it might help.

As an off subject regarding my AMG, do any know if there is a difference between the exhaust cam of the M104 280 and that of the 320? On the AMG 3.6 104 its believed that the intake cam is an AMG product while the exhaust is the stock C280 unit but with a new sprocket that we think is retarded from the stock 280 unit.

Now if the 320 has a diff exhaust more aggressive profile, it would be cool to try it with the sprocket provided on the AMG unit.

And I wonder why none have tried to use the AMG intake cams and exhaust on an M120!!! They should fit I think and they will make good power for sure. I have driven a 280C with the AMG cams on it and the car made serious power.

Thanks!,hopfully this time everything is straight and iv got the correct timing...everything lined up at 20atdc!.

Very Interesting! sounds similar to some of the issues im having with mine:

1-difficult to keep a low idle
2-massive amounts of boost down low
3-power dies rapidly after 6000,but this could be due to not switching of intake advance

Intereseting about tthe AMG cam sprokets,you would possibly have to compare them side by side unless you can find genuine MB/AMG info!.
Its pretty hard to get second hand AMG bits here especially cams etc,im waiting for a C36 rear bumper to finish of my kit,its going to be a while =)

If you feel power is fading quickly at 6000 its prolly from the advanced cam. But since you mentioned before that keeping the cam advanced past the 4200 range made a bit more power, you can opt to switch it of at say 5000 - 5200 and see the results you get.

Like i said before, in my AMG its clearly felt that the Cam needs to stay advanced past the factory set point at 4000 rpms, it can be a similar case for you too.

If i had a V12 M120 SL and the AMG cams could be fit, i would pay a couple of thousands for them, am sure they will give some 30+ hp on a 6.0, After all the 7.3 AMG M120 is nothing but 2 "3.6 AMG" engines in one. (Almost):P

Interesting so are the heads almost the same as the C36 on the V12 M120?

Hmmm,Just spoke to the tuners,they confirmed we did try switch the advance off at 4300rpm and it made no difference(or made it worse)...which is very odd!.so the dyno run i posted is with the advance on throughout the entire rpm.

Next time on the dyno we will try a few diferent rpms to switch at and see how it goes...

I have replaced my intake advance with a near new second hand one as sometimes when the engine is hot and is turned off for 5 mins then restarted it makes a grumbling noise,this was either the tensioner or the intake advance loosing oil pressure...i pulled apart the intake advance and there is scuffing around the main chamber from poor cleaning of the block after the machining.the new one had much tighter spline clearances and seems to auto slide to the retarded position much better then the original!

Just having the fuel rail remade at the moment,after that will get on the dyno.

Cheers,
Paul

Just for referance heres a dyno of the first tune,we had uncontrolled boost because of the wastegate position/piping,we have since ground it out nice and smooth whcih has helped alot,though we run 14.5psi now so its not such an issue.

This graph assumes cam timing is correct on both runs though they happened between engine builds so i cannot be sure.I have had to shift the blue line to its correct location as the software did not properly align them on the day,i have not shifted the afr curve.

Blue line is with intake cam retarded troughout the entire rpm range,boost is set at 5.5psi on the wastegate but gradually raises uncontrollably to ~14.5.(notice the problems with surge down low) rpm limited to 6000.

Red line is with the intake cam advanced throughout the entire rpm range,boost has been upped to ~14.5psi

From this its possible to see there will be gains in using the retard up high...but the retard will need to be better compared with the boost setup the same as the red dyno run.

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Cheers,
Paul

Well now that you have made the sprocket for the exhaust, you will have more gains and before 6000RPM. At Least thats what i expect to see. but one thing that you might have is an increase in low RPM torque and quicker spool up.
While tuning an EVO10 that has both cams adjustable, we set advance on the intake and retard on the exhaust, and we ended up with what i mentioned above.

SO Pags,

Any new updates??

every time i read something you two guys do i learn something,
thankyou very good reading of attempting to sort out your complex problem paul!