OK, so, I'll admit I didn't realize until recently ACD didn't allow more than 50% of torque to the rear. This makes me wonder about the following hypothetical situation: if your front wheels are spinning in snow/mud/whatever, isn't the ACD actually worse than the viscous differential? I mean, can't the viscous differential actually put more to the rear than 50%? Yes, I know it's much slower than the ACD, but in this case you wouldn't care that it took a few seconds to kick in, you'd just be glad it did.

 

I'm really curious as to this issue as well. One detail that was added to the '05s that should help the acd in this mud/snow situation is the front limeted slip. Hopefully somebody with more knowledge of drive systems can jump in, but it seems as though fundamentally the best that our '03 VC center diffs can achive is a 50/50 split, in that the center is effectively locked.

 

The ACD can only do a 50/50 split aswell, it just that it can play around with the locking strength and timing of it.

So in snow mode it will stay locked for longer than it would if it were in tarmac mode.

 

Nope. The VC locks up giving you a direct 50/50 split if one set of tires is spining when the others are not.... just like the ACD but slower and not as solid.

Keith

 

http://www.btrprep.com/evo_7.htm

http://www.btrprep.com/e7_qa.htm

This part is extra interesting:

"The system is technically far superior to the preceding Evo models VC centre differential systems (as in the US EVO8 as well I guess?). The centre differential performing well and able to limit front to rear axle “slip” on full throttle to a mean of around 0.6% on a slippery gravel surface. To put this in perspective, a good condition VC unit on a Evo 4,5 or 6 would struggle to be better than 30% aggregate slip value, which is traction going out of the window.
Pressure can be introduced and lost within the ACD system at speeds surprisingly close to WRC car standards, which has allowed Mitsubishi engineers to use a complex and sophisticated software control"

 

In other words, even when the VC "locks up" it isn't locked very well Lots of power going towards wheel spin in slippery conditions in the 03 and 04 I guess.

Keith

 

An ACD is superior because it can be tailored to your taste. Everyone likes a little different flavor when driving at the limit especially in traction limited situations.

Brandon

 

umm... to my knowledge there is an ACD ECU from ralliart..

Which makes me ponder Isn't the center diff electronic... If it is, then a Ecu can be theoretically set up to make 100% rear right?

If this is true... then ill 100% sell my car for an 05 because i always wanted to feel waht it is like in a rwd evo lol, actually id be happy w/ 80% rear-20% front...

 

I think the only way you'd achive this is to remove the front halfshafts while programming the ACD to lock fully. Of course now the ACD clutch will be transfering all the torque all the time and will most likely not last long. I'm fairly sure that the way our drivetrains are set up the best we can do is 50/50 split. The clutch part of the ACD only couples/uncouples the rear driveshaft. To split more torque to the rear it would have to have two sets of ACD clutches, one to lock the rear and one to lock the front. I could be wrong of course, but this is how I understand it.

 

Snow mode on the new 05 EVO's is 70% front and 30% rear

 

The ACD can not do any more than a 50/50 split, it doesn't change the drive ratio.
All it does is decide how hard to lock the centre diff and for how long.

Take snow mode, it will stay locked for longer giving torque to all the wheels for longer so to prevent slip, even when cornering.

While Tarmac mode will release quickly when cornering so to help prevent understeer and play around with the timing and locking strength/timing alot more than in the other modes.

 

100% correct!

I hate seeing page after page of missinformation with people saying you can have a 70/30 split biased to the front, or 70/30 biased to the rear..... ain't gona happen with the EVO!

Keith