PTS-BRG

I took the liberty of creating this "Master Thread" for any and all of us with tuned 991.2's who have the same shift flutter/bounce at redline from 3rd-4th gear, or anywhere else.

There is a lot of information spread out on rennlist, so I wanted to try and get in into one place, one thread, to see if those with the knowledge can figure it out.

I tested my car again and after a no flutter Saturday, it was back to bad flutter Sunday, which means that the problem isnt resolved. I can tell you that it has nothing to do with wheel sizes or offset or anything like that. The only thing I can figure that is common with all of us is that it ONLY happens on PDK cars, Not manuals.

I have been told it could be a limiter issue. A throttle blade issue. A PDK issue. An issue where the ECU throttles the engine based on PDK data. Perhaps clutch slippage, need to increase clutch pressure. This is happening on RWD and AWD cars. Base and GTS.

I will upload a video to demonstrate the problem, I also think the shift points from race launch are all over the place, but it is being uploaded to show the bounce from 3-4th gear.

I have also exhausted my patience waiting for Mitch or Cobb to solve this problem. They make a great product and Cobb (the company) has been responsive, but they have no answers. Its time to look to other tuners to see if they can solve it. Not leaving the Cobb platform, just looking at Pro Tuning with someone other than Mitch, who has left the company, is non responsive (to me) and who has tuned other 991.2's who are experiencing the same issues. So, Mitch clearly cannot figure it out. Maybe these are all cars that Mitch tuned? Need to look into that as well..

I have scheduled a re-tune with another local tuner who comes highly recommended and tunes race cars for a local Porsche race team. I will post back Wednesday evening as we are scheduled to do the tune early Wednesday morning.

2kRbx1O.mp4

usccharles

what actually happens between 3rd and 4th can you explain? it hits the rev limiter on 3rd into 4th?

PTS-BRG

Can you see the video I uploaded? It bounces around 7200 rpm redline for a few moments and doesnt snap into 4th gear.

usccharles

i don't see the link to the video..

PTS-BRG

It isnt a link, it is embedded in the post. I see it clearly. Let me attach a link here to those who cannot view it..

https://imgur.com/2kRbx1O

Jack F

Betim at BBI. He should be called and your issue discussed. Knowledge base in the shop is incredible.

PTS-BRG

Jack F: No idea who this person is or where the shop is located. If you have a contact number, shop address, etc. let me know. THX

991.two

Does this still happen with launch control off?

PTS-BRG

YES. Even if you just mash the pedal without launch it will still flutter.

spdracerut

My guess is the torque capacity of the transmission has been reached. Two personal examples of reaching the limit from a manual and a dual clutch (similar to PDK). My old track car was a S2000. On the stock clutch, it would hold a 1-2, 2-3, and 3-4 shifts no problem on a road course. However, on a 4-5 shift, the clutch would slip and the rpms would just shoot to redline. At the higher driving speeds, the rotating bits in the drivetrain have more inertia and the available clamping force of the stock clutch wasn't strong enough to prevent slip. I upgraded the clutch to one with more clamping force and the issue went away. The other car I drove with a transmission slip issue was a Mitsubishi Evo X with DCT trans. That trans would slip often in normal mode; quite disturbing. It was this really weird strong balking type event too. Not just like a clutch slip in a manual trans car. In sport mode, it would increase the clamp pressure by increasing the hydraulic line pressure in the trans and it wouldn't slip. When people tuned the car, they had to turn the transmission too for higher clamping forces. Of course, there are limits to the stock parts and once those limits are reached, upgraded parts are required.

Dodson is the go-to for dual clutch/DSG/DCT/PDK type transmission upgrades. They are used on all the 2000-3000hp Nissan GTRs. They make PDK parts, though I don't know if applicable to the 991.2.
https://www.dodsonmotorsport.com/porsche.html

PTS-BRG

Spdracerut: thanks for your reply and input. This was originally one of the possible culprits. However, the PDK in my car is the same as the one in the turbo S and it can easily shift that car with equal or more hp and torque. There have also been GTS’s and Turbos that have shown 700, 800 even 900hp without changing the PDK. I’m not saying you are incorrect, it just seems odd that the clamp pressure would be insufficient with such a modest bump in torque.

thesaintusa

For the 911s pumping out 700-900 hp did they have any tuning done to the transmission, i.e. not upgrading the PDK parts but adjusting clamping force?

Any way to reach out to the tuners of those cars?

PTS-BRG

I have spoken with a couple of guys with 700hp cars and they told me the PDK is just fine, no need to increase the clamping force or do a PDK tune.
My car isnt putting down THAT much power and there are half a dozen other cars probably putting down even less than I am who are having the same issue.
It even happens on Base Carrera's and X51 kitted cars.

Not saying it cant be the clamp pressure in the PDK, but it seems odd that it would only happen from 3rd to 4th shift at redline.
Doesn't the car put out even more torque from 4th to 5th or 5th to 6th? If so, why doesnt it happen there where the numbers are even greater?

thesaintusa

Good point.

Odd that it would only happen on 3rd - 4th shift and not 4th- 5th, or 5th - 6th. The PDK would be subject to more torque at the higher shifts.

Any way to monitor/log the clamp pressures in the transmission?

When was the last time the PDK was serviced?

PTS-BRG

The PDK was re programmed months ago via the Porsche PIWIS software. It is adaptive and learns as you drive. That didnt fix the problem.
The new Tuner plans on going for a drive with me on Wed Morning to try and see what the car is doing and how it is behaving.
Then it will remain with him for the remainder of the day for a completely new tune. Don't know what else to do...

I am putting out somewhere around 500ft/lb Torque so perhaps it cold be the limit of the current PDK firmware.
Stock GTS is somewhere around 400ft/lb so it is a fairly good percent higher than factory specs..