It does have 3 input shaft speed sensors. One engine speed, and two post clutch input speed sensors.... yet no output shaft sensors. Can’t think why they would double down on engine speed and yet have no output sensing?? They trust the DSC and not the DME? Why does it get its tits in a twist from a shorter ratio and not a longer one(
@dyezak is using stock diff with m3 calibration)?
The output shaft speed sensor is not required for shifting if there are sensor on the transmission side of the clutch.
To control the shift control SW is looking only at engine and transmission side of the clutch speeds.
Output shaft has very little to do with performing the shift and it would be too inaccurate because flexing of the drive shafts, backlashes, etc.
Output shaft has to do with shift scheduling though, because industry practise is to set shiftpoints based on pedal position and output shaft speed (in this case calculated from gear ratios or less likely ABS). But changing differential wouldn't help (unless for scheduling they actually use ABS sensors). But most likely those M3 GTS shiftpoints
are just low - this car has V8, so they can be low. Someone could confirm how really are they in M3 GTS.
I imagine this is because switching from a longer to a shorter ratio mimics clutch slip (higher rpm relative to expected rpm for a given engine speed)
I don't believe that would be the reason. In-gear is the time when plausibility checks would happen (to asses the sensors are working correctly). I don't know why putting 335i soft to M3 doesn't work. Maybe it is just luck that we don't hit diagnostic bands from one side, but we do from another. Or 335i has tighter diagnostic bands because they never consider people would swap differentials on 335i's.
You’re right. It would also explain why @dyezak’s car thumps into gear really hard going up the gears and fumbles the downshift.
Again, I don't think FDR has anything to do with shift quality. I would think more that different dynamic of engine control/engine inertia have more to do with it.
Still there is a chance that his problems are mainly due to reset clutch adaptations.