DME Tune Affects DCT Performance

dyezak

Major
May 4, 2017
1,768
Plano TX
Something to keep in mind. Your DME tune affects DCT performance. I was just working with a member who had poor shifts with his DCT and one look at his tune told me something wasn't right. There were no torque limiters being hit, no knock or timing corrections from knock sensors, but there was MASSIVE timing reduction at every shift.

datazap-chart (4).png


If you look at the blue/purple line that is timing drops without any knock or torque limiters. If you compare it to the grey RPM line you can see every dip in timing corresponds to a shift or an abnormality with post shift activity.

The individual got a new tune from someone with a great reputation on tuning DCT's and this is what it looked like after:

datazap-chart (5).png


You have the same car just a few days apart with a new tune behaving completely different. You still have a slight timing drop but nothing like the previous setup. Also, you can look at the grey RPM line and compare the shift speed no timing drop and timing drops. Even in the second tune you can see how the timing drop that did occur caused that shift to be slower than the first two shifts with no timing drops.

Just a public service announcement. Your DME tune impacts your DCT shifts even when (from a power standpoint) the tune is good.
 

boostE92d

Corporal
Jan 9, 2018
147
Houston TX
I'm getting timing reductions (post shift, dct) almost that bad with my car. I'm just running the ots MHD e50 tune. I wondered what that was all about. Knowing is half the battle. Thanks.
 

NoQuarter

Captain
Nov 24, 2017
1,048
Indiana
I'm getting timing reductions (post shift, dct) almost that bad with my car. I'm just running the ots MHD e50 tune. I wondered what that was all about. Knowing is half the battle. Thanks.
right... an E50 tune with DTC is going to be MUCH happier with a custom tune
 
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Reactions: boostE92d

Mevd17x

New Member
Aug 2, 2018
1
This is true, and the DME values have had an an influence on DCT and Automatic gearbox performance for a very long time. On the DCT cars there are maximum torque tables in newton meters that will limit on shifts if the tuned power exceeds the allowed limits, and on automatic gearbox cars, careful consideration of the optimal torque for lambda maps is needed to make more power whilst not bumping into transmission torque limits set in the DME.
 

RSL

Sergeant
Aug 11, 2017
345
What are the right torque tables to be looking carefully at?
It's not all torque tables, it takes a broader view and knowing how different things tie together. If you're having some questionable events and want to try to tackle them yourself, post logs. If you want a tune good in short order, no substitute for testing and experience, and doubt there's anyone that has more depth in tuning DCT cars than BQ.
 

Sbrach

Corporal
Oct 2, 2017
218
Interesting. I was under the impression the timing drop for the shift was necessary to reduce tq in order to complete the shift. What does tq actual look like in those logs?
 

dyezak

Major
May 4, 2017
1,768
Plano TX
Interesting. I was under the impression the timing drop for the shift was necessary to reduce tq in order to complete the shift. What does tq actual look like in those logs?
There does need to be a dip. It is hard to explain, but if you have ever thrashed a modern sport bike (motorcycle) you'll know the "feel" of shifting like this. You don't have to close the throttle completely on a bike to complete the shift, just enough of a lift to unload the dogs (going from 100% to 90% throttle).

Same thing here, there is a dip on the timing. But you don't have to go to -11deg timing to complete the shift. A mild drop of a few degrees is plenty to unload the input shaft to allow the clutches to swap.
 

Sbrach

Corporal
Oct 2, 2017
218
So I just did a test and at 380nm reported timing drops from 11.5* to -6 for the shift. Before, with stock load to torque, at around 575-600nm at the shift timing drops to -11 in some logs but as little as 4 in others. The duration is longer though.

I assume the above log is an n54. I have many tq Manager tables defined for N55 but not nearly all of them. If the tuner you are working with would like to share what tables are needed in MSD8x to keep timing nearly flat like that I will add them to the N55 xdf. I think a lot of the overshoot/undershoot around the shift that I am fighting trying to dial in PID May be a result of this large timing drop. I did check a log from my car stock and it does drop to around -6* as well.
 
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aus335iguy

Lieutenant
Nov 18, 2017
913
I think that N55’s and N54s are slightly different in approach to timing drops and duration as well.
Not in all cases but generally you can hear this as a typical DKG pop or burble as it completes a shift. It isnt as prevalent in N54 and that’s why i think that the strategy for shifting is different between the two.
 

ganque

Private
Jan 22, 2018
41
So... does N55 PWG with DCT are also affected by this? I'm planning on getting a custom tune next month.
 
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