The S-AWC in the Evo has a pretty complex AWD system and is still probably one of the most advanced AWDs you can get in a road legal car now. It's super fun to read about and when I left the scene in 2015, the only ones who were able to adjust [tune] the S-AWC was Bosch with their own unit, requiring you renting out an entire track for the day and paying for the services which if I recall correctly, started no lower than $20,000. I don't think that has changed.
- 3 hydraulic diffs: front, center, rear. All functionally open diffs. The center and rear diffs are active.
- System is always 50:50 front/rear power split
- 3 known sensor inputs: wheel speed, yaw sensor, and steering angle sensor
- When the power starts to bias towards front/rear more than the other, the center diff will start locking
- The rear diff can send 100% of it's given power to either side - so essentially up to 50% of the car's total power can be sent to either rear wheels (torque vectoring, also known as AYC-active yaw control for Mitsu.)
- There are 3 AWD settings, tarmac, gravel, snow.
- Tarmac allows the center diff to stay open the longest but will clamp the hardest once limits are reached
- Snow will lock the center diff the earliest but the clamping force is much more gradual than tarmac, essentially allowing smoother locking operations. This was a favorite with drag racers.
- Gravel is in the middle. Usually this was also a favorite when racing in wet conditions.
- The traction control and stability had 3 settings.
- Completely on - TC will disable engine power (horrific feeling I might add.) SC will operate the rear brakes as a way to help the rear rotate.
- TC off, SC on
- TC and SC off. Recommended for the track as leaving SC on will burn up the rear brakes
- Fun fact: There were high failure rates for the pump due to corrosion. The pump for the system was located behind the passenger rear wheel covered by nothing more than the body panel and wheel liner. If you lived in the salt belt, it wasn't a matter of if
your pump failed but when
and often before the car reaches 100K.