JB4 Reported torque and clutches slipping

[aus335iguy]

There’s been a couple of instances where people have reported DCT clutches slipping in circumstances when they really should be holding. Ie cars with reasonable but not over the top power levels; and some have even resorted to aftermarket clutch packs to resolve it only to find that the issue remains.
In some cases it’s been found to be related to how a JB4 / Back end flash is reporting torque. I just explained it (best I could) to some poor guy on the xhp what’s app group again.
I don’t fully understand it and I’m definitely not an expert
I do know that It’s not the JB4 that’s the issue specifically. It’s how it’s setup in the individual car by the tuner. It would be great if some of the more accomplished tuners could explain what exactly is happening as I really think people need to hear it. @WedgePerformance @Twisted Tuning @V8bait @Terry@BMS

 

[V8bait]

DCT can be frustrating at times but is a very good trans. In my experience, most people can run a ton of power through them, however some can't. One person I can recall in particular has a brand new unit and it is still acting up, he is flash only and the only "fix" so far has been maxing out the reported torque pretty much. I have a feeling it's related to software and adaptations but I'm not really sure. Before flash tuning was a thing, cars had major issues when running high power but reporting reporting factory levels to the DME with piggybacks. The DCT would slip and gearboxes would be damaged or fail every time. I do sometimes wonder if some of the issues people have are due to previous abuse, but the transmissions and computers also do a lot of adaptation so it's reasonable to believe a JB4 may be causing issues. For example, if you set the "backend flash" load to say 180 and JB4 boost target to 18psi the DME will see 180 load at full boost. Up boost to 26psi and the DME will see the same 180 load it did at 18psi. This was a huge problem before, when the DME only saw maybe 9-12psi and due to the flash tuning you can pretty much max things out now regardless, but how that actually effects adaptations is beyond my knowledge. Especially if people are fiddling with maps all the time, I know the DME watches shift times. To be fair, even flash only cars can experience problems so I don't want to throw the JB4 under the bus but it's a reasonable thought to have.

I've been tuning a few xHP DCT cars lately and so far my initial impression is that it seems like the software is helping. I've had to adjust the flash tables quite a bit, but in good ways in the factory direction. I still need to read up more on the changes, but the 335is already ran more line pressure than the M3 so I'm not sure if they were able to squeeze any more out or if they were better able to optimize things through the shifts, but it seems there are clear improvements especially if you tinker with the custom options. Only had seat time in one a couple times now so Ken would probably have more answers as he owns one, or Terry but I'm sure you know what he's going to say already.

 

[aus335iguy]

You make a good point. Once clutches are glazed there’s little chance of coming back. Thanks for your insight @V8bait

 

[carabuser]

Fudging the L2T tables to report higher torque at low load is just a band aid fix for 1 issue the JB4 causes.

What about every other table in the DME that references load? Just click through the tables in the DAMOS, half of them have an axis labelled Rf or at least reference a parameter that is modelled off of load.

I kind of understand people using a piggyback if DME tuning isn't available and they have a manual trans but there's no excuses on the N54.

 

[aus335iguy]

Fudging the L2T tables to report higher torque at low load is just a band aid fix for 1 issue the JB4 causes.

What about every other table in the DME that references load? Just click through the tables in the DAMOS, half of them have an axis labelled Rf or at least reference a parameter that is modelled off of load.

I kind of understand people using a piggyback if DME tuning isn't available and they have a manual trans but there's no excuses on the N54.

So is there a way to make sure it doesn’t have an adverse affect elsewhere ? Surely it can’t be all bad?

 

[carabuser]

In my opinion no. Most are very tactful when discussing the JB4 because Terry is a nice guy and the customer support for JB4 users is great but the argument for JB4 against flash tuning always distils down to the same points, it's been this way as along as I can remember.

"I've been running JB4 for 3 years and my car hasn't exploded"
"JB4 is great because I switch it to map 0 and run MHD"
"flash only can't do gauge sweep at startup? Checkmate!"

The market seems perpetuated by uninformed people giving the advice that as soon as you pick up an N54 you should spend a load of money on a JB4 and some useless hot air intakes and start sending it. The idea that code changes to an electronic module in a car can increase power is still witchcraft to most and the idea that this could be done from a mobile phone is just unfathomable.

 

[aus335iguy]

Here’s one guy who’s tuned mhd only 20psi 2nd gear reporting 600 and slippong

 

[jeremycnwy]

has there been any updates on this topic?
im waiting on a speedtech kit for my 335is DCT and i have run jb4's since 2010. i know and understand how they work and know all of the arguments for and against so i dont really want to de-rail this thread in that direction. With regards to the DCT is there a proper way to have the jb4 report torque values to the dme that are correct? is it a function of the back end flash?
what are the real world expectations for the clutches in the dct now that we have had time for these new developments with xhp to pan out?