If you've been following Marty's 2-door WRX STi you'll have seen he has performed a complete drivetrain swap, replacing the gearbox, differential, tailshaft, driveshafts, hubs, brakes, and struts with much-improved later-model STi upgrade parts (check out the gearbox swap HERE).
But there was one final part of the drivetrain upgrade he had to do to make full use of all the mad new parts. The dream of having a mad choo-choo mobile that grips in corners like a demon, but which lets you flick a switch and do huge skids, is one I'm sure we've all had. The good news for Subaru fiends is that this is actually possible if you have a certain piece of technology called DCCD.
DCCD stands for Driver Controlled Centre Differential and it is similar in concept to many of the systems used by Mitsubishi in their Evo Lancers (Active Centre Differential, or ACD), or the ATTESA system used in R32-R34 Skyline GT-Rs. Pro tip, don't ask Nissan owners what ATTESA stands for as they'll tell you "Advanced Total Traction Engineering System for All-Terrain" and you'll be stuck there all day.
First appearing in the Impreza Version 2 STi Type RA model, DCCD allows a driver to fine-tune the handling of their car through adjusting the amount of lock-up the front and rear diffs use. The normal viscous centre differential used in manual all-wheel-drive Subaru set-ups was replaced by a mechanical locking unit as well as an electromagnetic unit.
A thumbwheel allowed drivers to adjust the centre diff settings, which some people thought was moving the percentage of drive between the front and rear. However, it was actually adjusting the amount of lock the limited-slip diff provided so the DCCD-equipped cars could get better traction in different conditions (like the snow, mud, or many other places people drive rally cars).
DCCD was included in regular global-spec STi Impreza models from 2005-on (and a little earlier in Japanese models, naturally) in the new six-speed manual transmission. The GD-series STis did also get an Auto setting which let a computer adjust the tuning of the diffs on the fly, leaving you free to concentrate on whether that was some water splashing off your Hella Supertones or it was another headgasket in your EJ.
In 2018 Subaru moved to a completely electronic centre differential, which is surely filled with witchcraft and mystery that can only be unlocked by an electric space wizard.
When people started fitting six-speed gearboxes to their non-STi Subarus (like I did a few times Back In The Olden Days, kids) they learned there was some trickery required to make use of all the technology packed in the heft cog-swapper, including that sweet skid button!
The factory DCCD computer read a bunch of sensors, including ABS sensors, wheel speed sensors, G-sensors, as well as a steering rate and yaw rate sensors. From 2008-on these sensors were wired as part of a CAN network, meaning it is almost impossible to hook up a 2008-on factory DCCD system into an earlier car.
However, the good news is there are aftermarket companies who can sell you controllers for the electromagnetic centre diff, giving you DCCD control. And Marty has sorted one of these kits from the legends at IwireServices.com.
It is basically a "bolt-in" kit, just needing some basic power wires run and a couple of wiring plugs changed over, though you do need to be prepared to pull the interior of your car apart (and your top-mount intercooler off) to have the access you need to run these new looms and computers, as Marty showed briefly in this episode HERE.