MoTeC’s Subaru Diff Controllers (SDC, SDC2 and SDC3) are suitable for Subaru WRX and STi vehicles. They are plug-in replacements for the factory fitted Driver Controlled Centre Diff (DCCD) controller, fitting into the OEM box that is bolted to the steering column underneath the dashboard.

It is worth considering the installation of a MoTeC M800 Plug-In ECU in addition to the SDC2 or SDC3 to take advantage of several additional features. Using the RS232 serial communication link, all values from sensors connected to the SDC2 or SDC3 can be logged in the M800 Plug-In ECU, without having to duplicate any of the sensors.

Functionality
The SDC units are used to adjust the torque split between the front and rear differentials to achieve greater control over handling characteristics such as traction, braking on loose surfaces, turn in response, and understeer on both corner entry and exit.

The centre differential is essentially a limited slip differential with adjustable preload. The SDCs work by regulating solenoid current, which is proportional to the preload. When no current is applied (0% lock) the centre differential operates as an 'open diff' with a mechanical torque distribution of 65% rear and 35% front (60% and 40% in some vehicles). With increasing current (increasing percentage lock) the preload increases, requiring more torque difference between front and rear wheels before the centre differential will slip.
There are six selectable control modes: 0% lock, 100% lock and four user-configurable modes. These modes can be selected using the DCCD thumb wheel.