You have been Stuck!

PM me when you think the useful comments have run out, and I will do a one time "clean up" and close the thread while leaving it stuck for all to see.

Keith

Z1auto sells the Ralliart ACD ECU upgrade, but it specifically says its not for US spec models
http://www.z1auto.com/prodmore.asp?m...gmt&prodid=137

Also, in layman's terms ACD exists to keep the behavior of the car predictable under different road conditions. To me this is what it means and feel free to correct me if I am wrong, when the coefficient of friction (mu) of the surface conditions go down (aka when the roads get slipperly), switching to gravel or snow progressively induces more understeer on the car during corner entry and mid-cornering.
This is because no car is setup to be perfectly balanced in handling in all road surface conditions. Usually a car that is setup to have neutral balance at the limit during dry road conditions will tend to oversteer as the road gets wet (slippery). There is no such thing as a car with neutral balance under all road conditions. But ACD tries to compensate for that ;) .
If you have tried pushing your car during wet/gravel conditions with ACD set to tarmac or if you have an 03/04 EVO and pushed it during hard cornering under wet/gravel conditions, you know exactly what I am talking about. The car will oversteer like crazy (dangerous if you don't know how to handle it).
ACD does a lot more than just inducing more understeer it also tries to optimize grip during accleration. Its pretty obvious on how it accomplishes that with the info given above.

Goodjob!!! Terry S. {thumbup}

so, the Ralliart ACD ECU must interfere with other equipment on USspec cars. I has nothing to do with AYC. hmmm.

http://www.lancerregister.com/showth...threadid=65880

Theres some info on the ACD ECU installed in a USA Evo. I think its possible to trick the ECU into thinking AYC is there, therefore allowing it to work.

Regards,
Max

Awesome, thanks Keith. :thumbup: I'm going to look into the Ralliart ECU thing a bit then i'll shoot you a pm to close and clean.

Thanks again to everyone for the kind words and keep the good info coming!

Terry S

"The ACD allows the differential to operate in more of a free state when steering movements are made. 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 as you can see from this picture. (turning radius.gif) 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 wheels would skip and skid badly. (1) (3)"

Question: Given the front and rear have lsd's and work independent from one another, if the center diff becomes locked, how would the wheels possibly skip around corners when both the front and rear diffs slip. You could actually set up, by virtue of plates, and control which end slips (over/under steer) if the center was always locked. Doesn't Ralliart offer a center lsd replacement that fits the US 8? How does this fit in to the mix if all diffs have the ability to mechanically slip under pressure (cornering)?

Dave

The slip action in the front and rear diff allow the wheels on the different sides to move at different speeds than each other without binding up and skipping around... but when BOTH front wheels are traveling a longer or shorter path than BOTH of the rear wheels you have a difference between the front and rear wheel speeds that has to be compensated for with a sliping action in the center differential.

I used a welded center differential on my Galant VR-4 and parking that car was an absolute pain in the @ss if any tight steering angels were involved. Binding and skittering happen at high speed.... at low speed such as parking the car it was more like binding and poping as the gears in the rear differential ring and pinion tried to self destruct.

Keith

Slight as it may be, I understand how slow speed cornering would complicate a fixed mechanical center. High speed should mostly be absorbed by the tires, but I see you have done this already.

Thanks for your input.

Dave

I don't think the center diff becomes completely locked but instead think of it as the center diff providing more clamping force under gravel and snow modes while still allowing some slip (LSD). Compared to the tarmac mode which immidiately opens up the center diff under braking and cornering. In gravel and snow modes the center diff stays clamped progressively longer allowing some slip. What is means is the car is more stable under braking going into the corner, longer in each mode. This is because the center diff is forcing the front and rear tires to have closer speeds under slippery conditions which translates to a more stable and predictable driving experience. Controlled understeer vs sudden oversteer ...

Hey Mike1023

I have the same problem as you, but it only happens when the car is cold

if you find out more let me know

tks

ya i know only happens on cold start ups thats why im beliving it is that. but i dont thinnk i will find out becasue if bring to deal they will void warrney. i have nothing left of the car. so i dont know how they will take it lol. i will see if my mancnic has the tool for the test. if so great if not not cool lol. i can always but the stock batt in and see but i bet anything it is from cold start. and note this only happens when it is like 20F out side and the batt volta is at like say 10 or so. so its hard for car to start up

How does the ACD react to differences in lateral grip front to rear?

For example, using the same size tire with a different compound? Or using the same diameter tire but with different widths?

In other words, does the ACD clamp harder/sooner/longer in response to yaw (assuming the the steering wheel being turned)?


Great info by the way... very well organized!

Boy this is a hard question to answer ... by using different tires on the front and rear. You are affecting the level of grip provided in the front and in the rear which will either induce more under or oversteer, depending on where the there is more grip and what the difference in grip level is between the front and rear tires.
ACD will still do what it is preprogramed to do depending on the mode it is set at (Tarmac, Gravel or Snow) and what you steering, braking and throttle inputs are, but the results might not be predictable .... the senario will just be different depending on the tires.
Eg: in Tarmac mode with grippier tires in the front, the car most likely will oversteer ... again depending also on surface conditions ... likewise using grippier tires in the rear will induce more understeer in every ACD mode.

nice, well thoughtout review. I guess i'll be using tarmac much more....

wow, nice write-up on ACD. Very helpful!