ACD-Pro - Mitsubishi Lancer Evolution Active Center Differential Controller

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ACD-Pro – Mitsubishi Lancer Evolution ACD (Active Center Differential) Controller

ACD-Pro is a standalone 4wd computer, engineered specifically for use with Mitsubishi’s Lancer Evolution Active Center Differential (ACD). ACD-Pro’s formula based microprocessor applies its own signal (up to one hundred times per second) to precisely control the center diff’s clutchpacks. This gives the user an infinitely adjustable range between fully locked and fully unlocked states and can easily be adjusted on the fly. ACD-Pro does not need map changes or re-flashing for different road and traction conditions

Technical Details:

  • Advanced Microprocessor Based Unit
  • Dual-axis high resolution G-Sensor
  • Water resistant and dust proof enclosure (IP65)
  • Custom firmware with several internal modes (adaptive modes) based on driver throttle and G-Sensor behavior that switch on the fly automatically
  • ACD (Active Center Differential) locking force calculations use advanced formulas instead of static mapping or “lookup” tables
  • Easy to configure as Standalone -OR- piggyback operation.
  • Each control module is fully bench tested prior to shipment.

ACD-Pro EvoX Installation Guide: Click Here!

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  • Proven in daily driving and track applications for EVO 7/8/9 and EvoX!
  • Unique and exclusive Left Foot Braking option
  • ACD-Pro can be in MANUAL mode which controls pressure directly from the knob setting -or- AUTO mode which uses G-sensor and TPS inputs, working off our algorithm with the knob for “gain”. The Auto mode is able to respond immediately with very little lag and precise pressure control.
  • The hardware and firmware were designed to work together to be as “driver transparent” as possible. Our philosophy is that the less you need to adjust or monitor while driving the more you can concentrate on the road / race.
  • Most setups can use ‘Auto mode’ and work entirely off of the “gain knob” without any tweaking or tuning (highly recommended). USB tuning is available for hardcore tuners but most will find it unnecessary
  • The ACD-PRO unit installation requires connecting (6) wires only. The installer has the option to hard wire the ACD-PRO to the ACD Solenoid (located on ACD pump) or to connect the ACD-PRO to the OEM wiring harness.
  • works well for swapped vehicles, converting from VCU (vicous coupling unit) to ACD.


Installation Notes:

    • TPS connection can be taken from (tapped into) TPS line going to ECU. Power/Ground from a spare circuit (switched) with 10 Amp fuse.
    • E-brake can be connected to the wire after e-brake switch (ground when pulled, float/unconnected when released).
    • ACD+/- going to the ACD valve solenoid. ACD+ (black 18 awg) replaces OEM ACD line and ACD- (white 18 awg) replaces connection to ground.The ACD+/- should never short when there is power . Now the original ACD+ from OEM controller connect to the ACD IN wire for piggy back.
    • To check TPS it should read 0.4-0.6 volts when throttle is closed and about 4.5-5 V when throttle is fully open on the blue TPS input. After making sure of that you can checkthe pump connection by going into manual mode and turning the knob. As you increase knob setting you should see an increase on voltage between the pump terminals (multimeter probes on +/- of the pump) from 0 V all the way up to 8-10V. The pump voltage check should be directly done on pump +/- and not pump + and ground as ACDPro is a ground switching system.


    • ACD +/- and Pump +/- wires (black/white pairs on 6 wire/4 wire, 18 AWG cables) should not short connect when power is on. Disconnect stock controller’s ACD+ from the solenoid valve. Failure to do so will cause damage to the controllers.


OEM ACD computer wiring diagram here:


How ACD Works in an Evo:

    • Mitsubishi’s ACD system works by dynamically adjusting the limited slip locking state of the center differential clutchpack. When we talk about “lock” on the center diff, it should not be interpreted as a distribution of torque from front to rear, rather it should be thought of only as a clamping force – which locks the Front and Rear outputs together, and prevents the center differential from behaving like an open differential. This is not the same as Nissan’s ATTESA-ETS or Subaru’s DCCD (both of which adjust torque split) —

ACD is fixed at 50:50 FWD to RWD, but instead ACD alters the clamping force on the center diff’s clutchpack

    • , see diagrams below:



    • The ACD is a bevel-gear type center differential with a front/rear torque distribution of 50:50. The differential is controlled by a hydraulic ‘wet’ multi-plate clutch, where the clutches are made from high strength steel. The maximum limited-slip torque of the multi-plate clutch is about three times that of a conventional VCU (viscous coupling) center differential: IE: 3 times the grip can be transferred to the wheels that need torque. Although some drag racers still prefer VC for its simplicity, ACD is technically far superior to the preceding Evo models (and certain USDM models) VCU. When the car is accelerating or decelerating rapidly, ACD calculates what the optimum locking amount would be and then engages the limited-slip locking mechanism by applying pressure to the plates via hydraulic ACD pump and solenoid. This ranges between full lock (16bar pressure), full open (0bar pressure), and all points in between. The harder you accelerate or decelerate, the more it locks – for maximum stability and traction. If the front wheels are spinning faster than the rear wheels, then the ACD begins to lock the clutches up. The pressures that can be generated or removed by the ACD system occur at surprisingly high speeds!


    • If the amount of force exerted by the front wheels is less than the amount the clutches resist, then the slip is stopped and both front and rear spin at the same speed. However, if the force the clutches can resist is less than the force exerted by the slipping set of wheels, then the wheels will slip, but only by how much remaining force the slipping wheels overpowered the clutches. When turning, the wheels in the front have to travel a further distance than the wheels in the rear. This is because the wheels in the front travel using a larger turning radius than the rear wheels, so in order for smooth turning, the center differential needs to become open to allow for the front set to turn at a different speed. If you were to leave the center differential locked, the tires would skip and chirp on asphalt. ACD effectively allows the differential to operate in more of a free state when steering movements are made. However the preset ACD maps that come with the car are designed to be forgiving for average drivers in stock lancer evolutions, not true motorsport setups with high power engines in modified chassis and suspension.


ACD History

    Mitsubishi’s Active Center Differential (ACD) was first employed in 2001 on the Evolution (Evo) VII model. When the Lancer Evolution VIII model was released in the US in the spring of 2003, the Evo was outfitted without the ACD or AYC found in other markets. Instead, it was outfitted with the Viscous Coupling Unit (VCU) which distributes the torque evenly (50:50) to the front and rear wheels. This VCU was also equipped on the 2004 model year Evo in both the standard and RS models. Beginning with the 2005 model year Evo VIII, Mitsubishi decided to outfit the car with the ACD unit instead of the VCU. The ACD was available to all variants of the model: RS, Standard, and MR, In October 2005, the 2006 model year Evo IX was released to the US market. Again, as it was with the previous model year, the ACD unit was standard equipment on all variants: RS, IX, and MR.


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    • The evo transfer case houses the front differential and the center diff – specifically ACD clutch pak and the ACD activation ring piston circuit. The ACD / AYC Pump is in the rear passengers side fender / bumper. This pump produces hydraulic pressure to active the AYC and ACD circuits which operate from 0-145 PSI. It also has an accumulator to store pressure (around 300 PSI). This pump is connected to the reservoir in the trunk. The ACD ECU is located to the right side of the glove box, behind the passenger side kick-panel. The ACD hydraulic unit is housed in the engine compartment and regulates the hydraulic pressure of the multi-plate clutch within the range of 0 to 16 bar (235 psi). There are many different sensors used by the ACD when determining how it will control the center differential. ABS input, steering wheel angle, throttle opening, wheel speeds, and longitudinal and lateral movements of the vehicle are constantly measured by the ACD. Additionally, the driver can select how the ACD will perform by selecting one of three different modes from a switch in the cabin: Tarmac, Gravel, or Snow. When you engage the parking brake, the ACD is disengaged to prevent damage to your drivetrain and the ACD unit. The reason this would cause damage is because if you were to have an engaged ACD attempting to lock the center differential then you yank on the parking brake stopping the rear set of wheels from spinning, you are forced to attempt to overpower the ACD unit from keeping the rear wheels from spinning. This puts a tremendous amount of strain on the ACD clutches, the ACD hydraulics, center differential and your brake system.

Frequently Asked Questions

    • Q: What advantages are there in your Auto Mode controllers vs. Manual Mode and Semi-Automatic controllers available on the market?


    • A: We believe this automatic controller is one of the most advanced aftermarket Center Differential control systems on the market today. It is rivaled only by a few very expensive systems on the market in its ability to persistently try to give you the best traction in any given situation. What makes the difference? The use of high resolution G-Sensors and the mathematical formulas developed that are used to convert the measured data into usable locking forces. Utilizing a physics approach to calculating the locking forces required using algorithmic formula’s instead of the “static mapping” method usually combined with basic logic trees that are so popular with competitor products. Auto controllers can calculate and set the locking force with a 10 bit output range – that’s 1024 steps of locking percentage and the rate of change is “fluid” in that it doesn’t jump in large increments like static mapping tables simply have to. The formula’s were “mapped” and then tweaked using tarmac and rally drivers in real-world racing conditions as alpha and beta testers. Their input into the feel of the car was exclusively used to tweak the formula’s to shave time in the accelerating, cornering and braking programs. In Auto Mode the controller can shave literally seconds off of each lap.


    • Q: How does the ACD-Pro control knob work and what is the proper adjusting procedure for determining where it should stay?


    • A: The control knob for the system is used to scale the ACD “aggressiveness”. Fully CCW turns the unit essentially “off” which will increase oversteer and bias the rear wheels. Full CW gives it full “aggressiveness” maximizing traction and thusly increasing under-steer. In this setting the system will attempt to give you maximum traction at all times by trying to maximize the amount of ACD lock at all times. The system is infinitely variable between these two extremes. Start at lower settings (over-steer) and increase the knob setting until you find the car handles the way you would like it to in the corners. You can alter the setting at any time and on the fly as conditions change.


    • Q: What happens if the ACD-Pro is kept in manual mode at the lowest setting? is it RWD?


    • A: With ACDPro in minimum setting (manual mode) the forces applied to clutch plates that control clamping forces are non-existent. It is still a fixed 50:50 torque split, but the differential plates are in the resting state as you would have while cruising. There is no issue with wear at long distances as it is designed and tested by manufacturer for this state of operation.


    • Q: What does the left foot braking (LFB) feature do?


    • A: We are the only ACD Controller manufacturer that has this exciting feature for rally and ice racers. Here is how it works: When on a corner you might use your left foot to brake but at the same time use your right foot to apply throttle on ice or mud and we enable you to use the same throttle level to keep the ACD engaged and keep the two axles locked longer and stronger. If the throttle applied at the time of LFB, is at 30% or higher, ACDPro Controller overrides the breaking algorithm and keeps the ACD engaged based on throttle level and G-sensor inputs. This is a very strong and effective feature used on ice and mud from Finland to Australia. Q: Where should the ACD-Pro unit be placed in the car for installation?


    • A: The suggested location for installation of the control module is behind the dashboard in the knee crash pad area, there is a large open area behind the metal bars. Switched power and ground are also available nearby at the fuse panel to tap into. You may want to run an extension for the two ACD+/- wires where you can solder in the two wires you need on the F25 ACD connector.


    • Q: Where should the G-Sensor unit be placed in the car for installation?


    • A: The suggested location for installation for the dual axis g-sensor is on the horizontal metal surface under the center console. ~1 meter of wire between the control module and the sensor is provided for this purpose. Any other level horizontal surface will do as long as the sensor case can be attached firmly using epoxy or other strong adhesive. It should not be too far from the center of gravity of the car. Do not use 2 sided tape, or foam carpet tape, use a 2 part epoxy or contact cement made for plastics. Note the orientation arrow, and install the sensor with its arrow pointed toward the front of the car! (The wires exit the g-sensor module towards the front of the car. The screws in the cover face upwards.


    • Q: How do I run ACD-Pro as a piggyback and keep the stock controller?


    • A: If you want to keep the stock system, you can disconnect the ACD (at F22 Pin 8) and connect that to the controller. Keep the pressure sensor and pump configuration as-is and make sure the respective wires are safely and securely disconnected (taped).


    • Q: Does ACD-Pro work on vehicles with AYC (Active Rear Differential):


    • A: Yes, it is easy to configure ACD-Pro as a piggyback and keep the active rear diff fully functional and in place


    • Q: How does the OEM Tarmac/Gravel/Snow switch influence the ACD?


    • A: Contrary to popular belief, this switch does not change the torque split. The differential is geared at 50:50 and cannot be changed by the push of a button. What this switch actually does is quite simple. Each setting determines how long the ACD will delay in freeing the center differential after a steering input is made. In addition, it will determine how much locking force the ACD will exhibit on the clutch pack and center differential.


    • 1. Tarmac is the setting to be used in dry, paved conditions. In this setting, the ACD provides the strongest limited-slip clamping force of the three modes and will almost immediately allow the center differential to go into a free state upon detecting a steering input.


    • 2. Gravel is the setting designed for wet or loose roads. In this setting, has the second strongest clamping force and the ACD will delay in freeing the center differential for a moment upon receiving steering inputs.


    • 3. In the Snow setting, the ACD delays in freeing the center differential for much longer than the other two settings. Of the three modes, this one also provides the least amount of clamping power.


    • On certain JDM evo’s and USDM Evo X’s there is also a rear AYC diff with clutch paks (there are two, one for the left wheel and one for the right wheel) and the AYC activation ring piston circuits (there are two as well). It also houses the rear differential. (most high performance evos get rid of AYC and go to an aftermarket clutch diff here).


For improved handling on non-AYC evo’s (USDM especially):

    • we recommend to do this to the rear differential: