4WD Controllers

Do-Luck Japan recently released two 4wd controllers for the BNR32/33/34 Skyline GT-R and the EVO 7/8/9 late last year. For some reason most of the English information I found on them is from the UK. We got an email at Cosworth a short while back from the people at Sumo Power in the UK. I have no idea who sells Do-Luck parts in the US anymore. Anyhow, the addition of a 4wd controller can enhance (or screw up…) a car’s handling on the road or track. By tweaking the sensor outputs for longitudinal Gs, lateral Gs, and steering angle, the Do-Luck “D-ETS-M” (GT-R) and the “D-ACD-M” (EVO) controllers can adjust the amount of front/rear power distribution and the rate of gain by affecting the hydraulic pressure that squeezes the clutch discs together inside of the center differential. This can effectively alter the way a car handles to account for driver preference, weather conditions, track conditions, tires, etc by making a car turn-in better, power out of a turn sooner, understeer/oversteer, etc. The possibilities are endless…to a degree.

Somebody asked me the other day something like, “What’s the difference between the Cyber EVO ACD reflashing software (or reflashed ACD computer), the piggyback controllers (Do-Luck, Field, HKS, etc.), and the fully programmable units (Motec, Pectel, etc.) outside of their prices?” Diff controllers actually mirror engine controllers in a way. The Cyber EVO software is much like ECU reflashing software, the piggyback controllers are much like piggyback fuel controllers like the Apexi AFC-Neo, and the fully programmable controllers are much like standalone ECUs. “How much control do I want?” is the question you need to answer before jumping in to a diff controller. Let me attempt to break it down.

Just like ECU reflashing software can be slow and cumbersome to work with but effective, so is the Cyber EVO ACD reflash software. It comes with 12 pre-programmed ACD maps, but no datalogging. I think you can also send your ACD computer in to have it reprogrammed too but I don’t know much about that. That’s kind of like buying a mail order ECU reflash if you ask me (not truly tailored to you or your engine in particular). You only have the 3 slots that you can occupy at any given time and there is no labeling so it’s up to you to remember which map you have in which slot since the LEDs are already labeled on the instrument cluster. Also like a factory ECU, it’s control strategies are specific to what the factory (Mitsu/Nissan) wants the diff to do and not necessarily what YOU want it to do. This adds to the hassle while tuning, but if you have time, patience, and money for track time you can improve performance for minimal investment.

A piggyback controller like the Do-Luck and Field controllers are similar to piggyback fuel controllers in that you can only tweak the sensor outputs and therefore only tweak the center diff’s effectiveness. You are still limited to the factory diff computer’s minimum and maximum outputs since you aren’t changing any of the actual programming. The analog interface (knobs) is great for quick tweaks and gives you a good deal of control, but not full control just like the Apexi AFC-Neo. Obviously there is no datalogging, but bang for the buck is good.

A standalone controller like the Motec or Pectel units give you full 100% control by allowing you to fully tune it’s outputs. Just like a standalone ECU there are no bullshit factory strategies in the way. While a diff controller is very simple in theory (no lock, full lock, and everything in between) the factory controller still limits things like rate of lock and unlock, fluid temperature limits, minimum and maximum fluid solenoid duty cycles, fluid pump pressures, etc. These things are probably only important to serious racers, but they are things to consider if you are building a serious effort car. Full control is always best if you know what to do with it. If you have a standalone ECU like a Motec or Pectel, you can also build track maps based on all of the data gathered between the ECU and diff computer for fully detailed driver/suspension analysis. This can be done with the Cosworth EC Pro ECUs as well. Chances are if you’re spending the big money on a standalone differential controller, then you will also be spending the big money on a high grade standalone ECU.

Regardless of any controller, the center diff itself and the fluid pump both must be in good shape. The fluid pumps have in line filters in them and with use and abuse can clog. The diff clutches can wear which reduces the diff’s effectiveness AND contaminates the fluid. Sometimes people who build “serious” cars seem to forget about the center diff and control system. Two more wheels driving the car means double the drivetrain work, right? Nobody said it was easy to go fast. The diff itself can also be tweaked mechanically just like a clutch type limited slip diff, but that’s a whole different story…

The Motec controller allows 4 selectable programs plus full lock and unlock. It has a plastic case and microphone style DIN plug to keep cost “reasonable” though.

The Pectel Mitsubishi CDC goes all out with the vibration resistant aluminum housing machined from solid and the aerospace grade connector. Using combinations of the 3 LEDs on the EVO’s dash the driver can choose from 12 selectable programs (if I remember correctly) plus full lock and unlock. With a PC it can also be programmed in real time. I believe the Subaru CDC is only sold through Prodrive UK though.

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