20 Bar Clutch-Pressure for the DCT

This is why you need it!

The DCT (Dual Clutch Transmission) was introduced 2008 with the M3 E92 as the successor of the mediocre SMG transmission. It was promised to combine the best of both worlds, being very comfortable during cruising and at the same time being able to deliver very fast and punchy shifts in the higher Drivelogic settings. For nearly 10 years the DCT (delivered by Getrag) was BMW's transmission of choice for their M-Models (except for the X5M/X6M) and it also made a short appeareance in the 135i E8x, 335i E9x and Z4 35i. It utilizes 2 separate clutches and gear-sets to seemingly switch between gears. Shifts are "overlapped", which means one clutch closes, while the other one opens simultaneously to deliver seamless shifts.

Rated at 700 Nm (520 ftlb) the DCT offered plenty of reserve when entering the market for the M3 E92 and 335i in 2008. However, times have changed and that 700 Nm often get exceeded by far in the Aftermarket/Tuning World nowadays. Even the stock BMW M5/M6 F1x touch that limit with their Competition variants delivering 700 Nm from factory. Unlike the ZF-Automatic Transmissions, the DCT does not employ torque limiters per Gear to protect it's internals. Slipping Clutches in the ZF 6HP/8HP will trigger torque limiters sent to the Engine Controller, to quickly get everything in check again during driving. Often this happens completely unnoticed by the driver. The DCT however, won't do that. It will try to raise pressure until it hits the 17/18 Bar limit, but then clutches will just slip. In case of minor slip this might get unnoticed by the driver. Most people do not feel a few 100 RPM slip, when being overwhelmed by the sensation of 700+ Nm put down to the road. In this case slip will just continue until one of the clutch temperature monitors starts to trigger and you are left with a "Overheat" Message in the iDrive and Limp-Mode. Of course your clutches have taken a substantial beating already at this point.

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 10000 miles. Of course this issue gets aggraveted by piggy-back 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 ran within it's 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 a 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 ftlb 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, a FBO M4 with S55 engine can easily get close to the DCT's limits, while the M5 with 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 1000 Nm/773 ftlb of Torque.


How much Torque your clutch packs are able to 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 car. While raising the Pressure Limiters in the transmission will help anytime, the effects will get even better when paired with a correctly setup engine tune. Running 1000 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 correct in the first place. This small time-frames are the difference between a clutch pack surviving 15000 miles or 100000 miles.