But even if slip only occurs in a small range each time you mash the throttle, there will be extended wear on the clutch packs, which then often leads to DCT transmissions ready for the trash within a few thousand or maybe 10.000 miles. Of course, this issue gets aggravated by piggyback units or poor engine mappings, which manipulate torque calculation inside the ECU and let the transmission run with too low oil pressure from the beginning. In such circumstances, the DCT won't be able to survive even when it runs within its stock torque limits.
With the stock calibrations, the 1st Gen DCT (E-Series) is limited to 17 bar of clutch pressure, while the 2nd Gen units (F-Series) employ an 18 Bar limit. Those limits are the same in all BMW calibrations, regardless if it's a 335is E92/M3 GTS E92 (both 17 Bar) or M4/M4 GTS/M5 Comp. (all 18 Bar). A stock M4 running around 600 Nm/440 ft-lb will of course never touch that limit and there's plenty of room to compensate for very high oil temperatures and nearly worn-out clutches. However, an FBO M4 with an S55 engine can easily get close to the DCT's limits, while the M5 with an S63 engine reaches the 18-bar limit just with a Stage 1 software tune.
Usually, slip starts to occur occasionally when being right at the limit and then happens more and more often over time, as clutch quality decreases. How quickly that happens depends on the quality of your tune and your right foot. Fortunately, both DCT generations have plenty of room to increase the clutch pressure and let them safely operate at much higher torque levels. Currently, we are offering 20 bar mappings for all DCT vehicles, which opens up room for around 1,000 Nm/773 ft-lb of torque.
How much torque your clutch packs can withstand is influenced by many factors, including oil temperature (holding capacity gradually decreases with rising oil temperatures), the current wear state of the clutch packs, the quality of transmission oil, and foremost a correct engine tune setup. Current torque is not measured during driving, but it gets calculated within the ECU through various maps and then sent through the CAN Bus System to all other units in the car. While raising the pressure limiters in the transmission will help anytime, the effects will get even better when paired with a correctly set up engine tune. Running 1,000 Nm of torque on the dyno, while only transmitting 800 Nm on CAN-Bus will have the transmission to adapt pressure all the time, instead of calculating it correctly in the first place. These small time-frames are the difference between a clutch pack surviving 15,000 miles or 100,000 miles.