https://www.cobbtuning.com/accesspor...transmissions/

Looking at COBB's PDK tuning for the 991.1 cars, the factors of interest are the 'shift firmness' and 'increased clutch firmness'.

"INCREASED SHIFT FIRMNESS

Shift firmness is the culmination of a few variables that determine how quickly the clutches are engaged between gears. The COBB PDK OTS maps offer slightly increased firmness over stock which translates to a shift more akin to that in a 991 GT3.

INCREASED CLUTCH PRESSURE

Minimizing clutch slip when engaging a gear moves power through the drivetrain more efficiently. Our calibrators have increased clutch pressure only in the High Torque Aggressive OTS map. This is intended to be used on vehicles that have a significant increase in torque over stock (50% or more). As a note, when flashing the High Torque Aggressive map, a PDK Relearn MUST be performed."

Assuming the clutch pressure is sufficient, then the variables that play into shift firmness are my guess as to the issue. I imagine it's the interaction of engine torque, shift pressure, and shift timing. So, for example, on a motorcycle with a sequential dog box transmission, you can do clutchless upshifts. First, you apply a little bit of pressure to the shift lever to preload it to get ready to upshift. Then, simultaneously, breath off the throttle and apply more pressure to the shift lever and it'll pop right into the next gear without using the clutch. If you don't get the timing correct with the lifting of the throttle and the moving of the shifter, it won't shift gears.

A link to how the PDK works:
https://autoweek.com/article/technol...oweek-explains

"A DCT is more similar to a manual transmission than a traditional automatic, but instead of one clutch engaging with a flywheel, two separate clutches work together. A PDK gearbox uses hydraulically actuated wet-clutch packs, one enveloped around the other. One clutch connects reverse, first, third, fifth and seventh gears, the other handles second, fourth and sixth. As opposed to a clutch pedal on the floor, an electronically controlled valve body actuates the correct clutch when it’s needed. The PDK only engages one clutch at a time. However, because gear sets alternate between clutches, as one disengages the other can engage in one fluid motion."

So.... maybe this shifting issue is an issue of timing between the engine torque being cut briefly (can be throttle plate closing and/or ignition cut) and the switching of the clutches. Basically, the shift firmness and how long it takes for the clutches to switch.

Now, if we assume it is in fact the clutch slipping, then I can see it slipping on the shift and then the engine hits the rev limiter which results in a fuel cut which reduces the torque enough for the clutch to catch. I don't know if it's possible to datalog what the PDK is doing in relation to the engine when a shift is commanded. As the same PDK is used in the Turbo cars, maybe someone just has to figure out how to tune the PDK on the 991.2? I'm sure the 991.2 Carrera has a different PDK tune than the Turbo as the engines have different characteristics. Or maybe, if it can be tuned on the engine side to have a slightly longer duration torque cut during the shift.

I'm purely hypothesizing as I don't have any detail knowledge of how the engine interacts with the PDK nor how the PDK programming works.

 

Looks like it's just hitting rev limiter and reacting in a funky way. Video has no sound.

IMO, you modded it and it's not working as per design...you're on your own. Surprised Cobb isn't helping you...nice learning experience?

I typically don't rev to redline in mine because it sounds and performs best under 6k.

 

That's not what happening.

...

That's wonderful. You're extracting less power from your car as it makes the most power above 6k RPM. It also has it's best howl above said RPM... With that said, I don't think this thread is for you.

 

Thank you all for continuing to comment.

Spdracerut: What you suggest may very well be what is happening. It is one of the things that Cobb felt could be the problem.

Minthral: I don't know why there isn't sound. I have sound on my end, but the video is mute. I will look into that and maybe upload again.
It definitely looks, feels and sounds like it is a rev limiter problem to me. But It is happening BEFORE redline, it continues to bounce until it engages.
It seems as if the car is unable to shift and the ECU has to "retard" something in order to get the rpms lower where the engine can engage.
If it was a rev limiter I would think it would engage beyond 7200 and mine is happening around 6800, well before the actual redline, but I really dont know..

As far as where "I" Shift, that isnt up to me. When the car is in launch mode its basically mash the pedal and hold on. The car determines where to shift, not me.
So if decides to shift at 7000 then its the ECU doing that. I think stock cars may perform better at 6k, but my dyne charts and my *** knows that there is massive power up high from 6-7000 rpms.

If I shifted at 6000 RPM's I would never have the times I have shown on Dragy.

 

Ok, here is the video with sound. It is a setting within IMGUR that only allows sound from IOS or Android devices, not laptops.
I re uploaded it. Same video now with sound. Just click the sound icon on bottom right of image for sound, It will still default to mute.

https://imgur.com/unkjbEU

 

Although its probably tq related, you should be getting more tq in 1st and second gear (1st gear is funky too but 2nd gear is fine). I agree its probably clutch related as others point out. The gearset in the carreras is from the 991.1 turbo but i would assume the clutch packs are totally different in the turbo models. Easiest way to find out is if there is a different part no for the turbo pdk.
I would imagine this can only be fixed with a TCU tune or by dialing back tq in 1st and 3rd gear. But even with a TCU program that increases pressure, you might be at the mechanical limit of the clutch packs. Is the juice really worth the squeeze with dodson for the last 0.2 sec? Might be worth it if your pdk broke, but not if its working. Its so expensive and your car already runs 10s. Maybe 11.0 if you dial the tq back a smidge. Thats still smoking fast. Turbo S’s are running mid-high 10s stock on dragy and one guy posted a 10.56 with a cobb tuned turbo S wih an akra exhaust. Half a second is nothing.
just food for thought

 

I would never even consider a Dodson PDK. I would sooner dial down the car before changing the PDK.'
I am not a racer or a drag racer or track car guy. I am just having fun trying to extract the most I can with simple bolt ons.

I am hesitant to believe that my car with 500ft/lb of torque is causing a PDK failure. I think a simple tweak to the tune or PDK software could correct this, but I am speculating.
There are cars pumping out far more torque and HP than my car does and using stock PDK. And, I think the torque is actually higher in other gears, so why is it happening just from 3-4th?

Anyone reading this and being hesitant to get your car tuned, DONT. It is the most fun you can imagine taking a fast car to super fast for very little money and it can go back to stock tune in 3 minutes.

I am just trying to figure it out for everyone else (and myself) in case anyone runs into similar problems.
PS: If I shift manually this is a non issue so it has to have something to do with the PDK and the programming with the tune/ECU.

 

I had the exact same issue in mine even before the upgraded turbos but after my last tune and pdk tweak (if that's what you want to call it) the issue has Not reoccurred.. Mine would hang-up between 3-4 before shifting even after it was at normal operating temps. Also keep in mind I'am at 550wtq at only 3k..

 

Cosmo: Are you suggesting a different tune solved it or a PDK tweak?

Do explain what you did to resolve it.

 

Yes when they went in the second time and had a lot more time with my car to figure out this issue it was fixed.. I have had zero issues with it and have ran many cars since. Steve is the tuner at Hydra and is the one who figured this out, give him a shout.

 

I actually sent him a message days ago . Waiting for him to get back to me or maybe I will give him a call later today.

 

If anyone can figure it out it will be Steve at Hydra. They have "fixed" many many Cobb tuned cars. I know people find that hard to believe but I've seen it and know the owners of the cars!

 

Interesting... That would drive me nuts. Enough to remove the tune. What a bummer OP. Hope you get it worked out.

 

It drives me nuts, but not even remotely nuts enough to ever consider removing the tune. Its a different car.
Like a good looking girl with perfect skin or a supermodel with a tiny pimple. Ill take the super model with the pimple over a good looking girl with perfect skin any day

 

I've mentioned this before, but I had the 3-4 issues too but it's been resolved. I was never able to capture it on a data log but my map was changed out for another one nonetheless and it hasn't occurred. I've been on this tune for several months now.

PTS, can you post a 3rd gear log starting at 2500RPM so we can compare it to my log which is "flawless". We are both Cobb and the same guy tuned our cars.... I know you mentioned that Cobb gave you a PDK tune of some sort, I never had that or was never offered that.

Have you dyno'd your current setup? I'd be curious to see if it happened on the dyno and what kind of numbers you're putting down.