Sorry guys... it is the shift... and it's not the shift.
I've posted about this in another thread
here, but it's an artificial delay the DME imposes between shifts on 6MT cars, both N55 and S55.
My testing, which you can see in this thread, suggests (with a lot of data), that there is a 2 second delay in waste-gate behaviour started from when you first lift off the gas for the shift. The waste-gate doesn't fully close until this 2 second duration is up, and that slows the rate of boost spooling.
Shifting faster actually makes the situation worse, not better, because you'll feel the delay for longer.
Shifting quickly at higher RPM can mask the situation because less boost will be lost between your shift, but logs show that it's still there.
I've been working with a tuner to eliminate this delay, and it's going really well. I'm basically on the base map from my tuner intended as a starting point for 91 AKI fuel, combined with changes focussing on this waste gate delay and lost boost between shifts. My tuner is still trying to make it more consistent, but it's already about holding boost between 2nd to 3rd shifts about 80% of the time, and 3rd to 4th shifts about 50% of the time. Butt dyne and Draggy data show that the car is way faster once the shift delay is eliminated.
I went for a drive to run some errands over the weekend with the Draggy running, and only just now looked at my data. I stated in this thread that my previous best was 5.12s I believe, but without really trying that hard I now have valid draggy from street 0-60 of 4.45, 4.48 and 4.47 (1ft). Screen captures below:
Of course, I cannot explain how R&T testers were able to achieve their results, but I actually suspect BMW may have had custom flash for the DME on those cars.