I just began noticing it recently but went back and looked at some of my past logs and I see it in them too. So this problem has been with me since at least Stage 3 and it's definitely limiting the performance of the car in the quarter mile. The issue is PDK shift lag. I am hitting the rev limit on the engine because the engine is faster than the PDK when using sport plus in auto mode. Look at these plots and you can see big gouges in the MAP when the rev limit is hit.

I went back and looked at a lot of logs I have collected and about 80% of the time that the car hits 7136 RPM, the VTG rate on both turbos drops to 20% irrespective of what is commanded. It stays that way until RPM drops below 6400 and then ramps back up to what is being commanded. The consequent result is a drop in MAP that can be seen in the graphs along with the drop in RPM.

When the PDK shifts properly, RPM drops and MAP holds steady and bumps at the bottom of the RPM shift point. This is where the power is and that propels the car forward at a continued increasing rate of speed, i.e. acceleration is still positive.

When the rev limit is hit, the boost drops so power drops and at the bottom of the RPM curve in the shift, there isn't any extra power, that application is lost. So the acceleration is lost during that time. That's obvious in the comparisons of the first pair of charts I show from two runs at the CR on Thursday under decent weather conditions. The only problem was that the Vbox was getting a lot of low sat readings and so I don't have Vbox data for every run but I did get it for the first and last which the two in the first graph are. The left is the first and the right is the last.

There is a definite difference that can be seen in traction loss vs rev limiting. When traction loss occurs, boost holds but speed remains flat or drops. When rev limiting occurs, boost drops and speed goes flat.

I am not sure what I can do to address this as not all PDKs do this and mine doesn't do it all the time. Clearly I can get clean runs out of the car but I could easily feel that loss on the last run from Thursday. It wasn't a traction loss, it was a hesitation and it took me a while to realize what it was as I looked over the data and other plots.

I had my best run with stage 4 and overall at the CR (1/13/2017) the first day I took the car out after finally getting it all back together and with the OEM diverter valves. That is shown compared to the best run from a year before at Stage 3 on the county road. The tires slipped in the Stage 4 run as they are the same ones that were new a year ago and it was 15 degrees hotter as can be seen in the IATs. Still, the Stage 4 result produced the same ET but with higher trap speed even given the limitations. I think if I can deal with this PDK rev limit issue, the car will finally produce numbers I want. Even with the rev limiting, it consistently hits 10.6 with bad tires out on the county road and traps above 130 on 93 octane.

The last plot is a run I made at SAR in Nov 2015 with a trap above 135 and an ET of about 10.7. It has that rev limit in it but that was on race gas. Notice how there is no wheel slip but the rev limit slowed down what was otherwise a very good run.

 

It was nice as usual chatting with you about all of this William. I can turn down the power little to help the car shift but that's going backwards. PDK software is right around the corner it's almost ready. Hang in there and in the meantime let's get a log with manual shifts to confirm. Talk soon

 

I talked to the Porsche service rep this morning and he says the PDK service isn't needed until 120k miles which would involve flushing and replacing the fluids. He said they could reflash it for me and then let me drive it with the new setup and it might adapt. I think that is my best hope for now. He said they could do that in an hour and I could just drop by next week so I am going to try that.

 

I agree on that one! Flash and maybe even calibration. Depends if you have the latest software or not.

 

I do, I checked that back in August when I had them do a 20k service. I was already doubting my PDK back then so they checked and told me it was up to date.

 

Interesting... will be curious to see how you resolve this. Hope it's within the software adaptation range as that's cheap and easy!

 

I just dropped it off but I am getting a set of the new PZero N1s as well in case this has to do with vulcanized rubber. Obviously I would rather not change two things at once but one trip to the shop is easier than two. The weather sucks here right now so it's a fine time to lose the car for a couple of days.

 

Update from the shop is that P1647 is a failure of a secondary coolant flow to the turbos when the car is turned off or the temperature of the engine bay is over 190F. So it's quite probable that this was what caused the limp mode failure to shift out of fourth at SAR. They will have the part in tomorrow and they are fixing it under warranty. Don't know if I will get the car back in time to make a run on Friday and this weekend I am booked. Looks like CR testing won't take place until next week.