I've read the ACD threads, and I understand the center diff is physically geared for an even 50:50 split.

However, I keep seeing articles from magazines (like C&D), where they say the EVO 8 and 9 with ACD are front-biased, with the ability to send power to the rear when needed. So according to them, the car is either 100:0, or 50:50.

I was always under the assumption that the rear wheels were constantly being driven. Am I wrong, or are the editors at C&D idiots?

 

The EVO is a 50/50 front to back. The AWD car they must be thinking of, would be the MS6, which is a 100/0, front biased.

 

Interesting... I'm attempting to find the C&D article; as soon as I do I'll post it here. In the meantime, I found this about the 2005 MR - and they too say the EVO is front biased with a variable split of 100:0 or 50:50

http://www.theautochannel.com/news/2...26/013512.html

Edit: I found the C&D article here.. read a few paragraphs down.

http://www.caranddriver.com/article....&page_number=1

So either these two publications have no idea what they're talking about, or we're confused.

 

It is always 50/50. The distribution never changes.

 

There is a nice article on the ACD if you care to read it

https://www.evolutionm.net/forums/sh...d.php?t=175195

I can try to summarize your experience if you so choose.

ACD Settings:

ACD is set a direct 50/50 ratio no setting in the ACD switch actually changes the torque bias. Instead the switch itself tells the ACD how much clamping force and how long to wait to release based on steering input. The ACD will start to lock up the clutches when the front wheel spin faster than the rear. The ACD will then release those clutches based on a timer setting based on steering input.

Tarmac - Highest clamping force to the limited slip diff clamping force. Any steering input puts the center diff into a free state near immediately.

Gravel - Medium clamping force, 2-3 seconds delay to freeing the center diff

Snow - Weakest clamping force, long delay (4-5) seconds to free the diff.

 

^^^ Thanks RoadSpike.. that was one of the first posts I read prior to purchasing my EVO. I just thought I misunderstood since even Car and Driver claimed the AWD system in the EVO to be front biased with a variable split.

 

My understanding isn't complete mind you but here's what i think.

From what I can gather the Evo has NO torque bias whatsoever. It simply powers the front and back wheel sets with equal force. That being said when the front wheels start to spin faster the center differential locks up making the car turn into a 4x4 system until the clutch is released., this only happens on ACD systems btw.

Now armed with the 50/50 torque split knowledge the may behave similarly to a front wheel torque bias simply based on what wheels are easier to break loose under heavy acceleration, that being said obviously the front wheels. The reason is dubiously simple, the weight of the car shifts towards the back putting less pressure on the front wheels allowing them to slip. This of course is probably how C&D assumed it split 100/0 to 50/50 which is flat out wrong.

 

Wouldn't changing the clamping force via the ACD selector switch technically change the amount of torque being distributed rearward.

 

Does anyone have the Motec ACD computer replacement? It would be lots of fun to have a 40/60 F/R bias for some throttle oversteer

 

Yes in a way, the ACD is geared simply to a 50/50 the clamping acts in the same way that a LSD would. Its not a TRUE torque bias in such that excessive amounts would make your car act more RWD.

Without getting into the details of how LSD works it simply allows for a greater range of torque split than 50:50 while not bias'ing it toward any one side or in this case front to back.

 

The center differential GEARING is set at 50:50. Without the ACD mechanism this is how the car would always operate. Just like an open rear diff is 50:50.

The ACD mechanism DOES change the torque delivery so that it is no longer 50:50 when tire slippage occurs. It moves more % of the torque delivered to the wheels to the side with more traction.

 

Interesting stuff guys.. in your opinion, how would our ACD system compare to the electromechanical DCCD drivetrain in the Scoob?

Granted, having come from an M3 - I'm biased towards RWD sports cars, or AWD vehicles with a rear torque bias. However, everything I've read lends to the fact the ACD or Mitsu AWD system in general has a slight edge in terms of track performance. Of course when I say track, I mean tarmac and not an off-road rally course.

One last thing; does anyone here know if an in-depth, technical comparison exists between ACD and DCCD? If so, could you please provide a link. Thanks.

 

I think I read in car and driver where is was 60/40 or 100/0 but that was a long time ago when i saw it

 

No.

 

They are wrong.