fantastic review! it's just amazing when people in the community freely share info of this caliber/ show just how far down the rabbit hole we can still go with the US evo. do you have the stock rear diff?

 

I still have the stock rear diff. Most of what I've been told is that the best bet is to consider changing the stock front diff out to the Ralliart LSD and leave the rear alone.

 

Just curious who you heard that from? is that a tarmac recommendation, or a dirt recommendation?

I'd also head the Ralliart Front LST was the best, but I couldn't stomach $3500 before installation, so I went with the Cusco RS clutch diffs for my car (1.5 way front, 2 way rear). I'm running Redline Heavy Shockproof in the TC & rear diff, and I can tell you it locks up pretty aggressively...but I never really got to mess around with the stock diffs so I can't offer much of a before & after on them.

Your reivew of the ACD ECU really has me itching to get on too.
Dave

 

That recommendation came from ACP, and he feels that it would apply for both gravel as well as the loose surface tarmac condition we see at Targa.

 

I just dug this up...appears based on the part number that you may have an ACD ECU designed for rally duty.

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

Any chance you'll be trying out the other box WORKS offers for comparison's sake? I'm curious about the 6 settings that box comes with, as I'm not sure I'd want to start fiddling with the settings without having some base settings (or more aggressive than stock) to compare to.

Dave

 

I don't plan to mess with the Motec unit for Targa. For a dedicated rally car, especially considering the level of competition that you run in, I think it would be worthwhile making the plunge and then tuning the ACD to match what you want it to do under various conditions.

 

Have you considered the TRE rear diff upgrade/rebuild? I'm not sure how well it would work on looser surfaces, but it works very well for smoother tarmac (i.e. street/road race). It eliminated the mid/late corner push in my car, which is still on a mostly stock suspension (i.e. no upgraded swaybars, springs, struts).

l8r)

 

Ok so the moral of the story is the Rear diff needs to lock more...and sooner then stock. Now...is it more RELILABLE (on the acd pump/drivetrain) to do one or the other?

 

All the diff controllers do is control the center diff and how much lock exists between the front and rear. Changing the controller theoretically should not alter the longevity of any of the parts.

Everyone I've talked to about the diffs on this car said that the order of importance on upgrading the diffs is center first, then front, and rear last, as that is the order of impact on the handling characteristics of the car.

 

Anybody know if the ACD controllers are the same between an Evo VII and IX? ... If it doesn't plug in, the answer is obvious...but if the plugs are the same, are the pin-outs the same? I have a friend with a VII who's willing to let me borrow his ralliart ACD box, but I don't want to damage it if the wiring isn't the same.

Dave

 

Almost everyone...IMHO...

The front diff only needs to be addressed if you have an VIII with an open front diff, otherwise the stock unit is excellent. The car will never stop pushing with an open front diff.

Next up is the rear...using a tighter center diff to send more torque to the rear with a stock rear diff does not fix the true problem, which is too much torque going to the inside rear wheel, and you get much better results from changing the rear diff than the center. In fact, the stock center diff, ACD or not, is perfectly adequate and already sends plenty of torque to the rear.

I have an '04 RS and have only touched the rear diff. I can make my car loose in, mid, and out or tight everywhere in the turn just with ride height, tire pressure and shock adjustments.

The 'magic' of the EvoX comes from the new active rear diff, the basic operation of the front and center diffs has not changed much. The new active rear diff does the same thing as a rear diff upgrade on an VIII/IX, just a little more intelligent about it with computer control.

 

David,

I think part of the reason for the differing opinion is the surfaces being raced on, and the car's we're working on. Your upgrade sequence makes perfect sense for cars without ACD, where the upgrade path that Peter is talking about is coming from the cars with ACD.

For loose surfaces, the ACD center ups the line pressure over the tarmac settings, so while the tarmac settings are ok, the benefits from upgrading to a ACD ECU that allows for higher line pressures can make a tremendous difference, especially in the loose stuff. Lots of people were talking bad about the ACD system, but few have been willing to jump into the programming to see if it makes a difference. I applaud Peter for jumping in with both feet, and I think he's been happy with the resulting vehicle dynamic changes.

The other benefits from upgrading the diffs is the availablility to mix multi-way diffs to change handling characteristics. I've got a 1.5-way front, and a 2-way rear Cusco RS diffs, and my next mod to the car is going to be to the diff computer. I'm just trying to decide if I think I can do an adequate job trying to mess with the maps myself, or if I should just trust the Ralliart folks that the Group N set-ups are good enough, even though my powerband will be vastly different from a proper Group N car.

Dave

 

Based on the webite you reference above:

"Three variants of ACD electronic control unit exist. The production version and two Ralliart variants - RA553831K1 being listed as a fast road unit and RA553831K2 a Rally unit."

I found this site: http://www.japanparts.com/db/partsli...maker=3&page=3

Toward the bottom of the page, this vendor has three ACD/ECU upgrades from which to choose. I'm interested in the first one that reads:

For Wet - Circuit. Won't fit a unit with AYC. For Evo9, will fit RS only. Manufacture

Parts No. is RA580728K1...$566.37 is doable.

This is a different ACD/ECU from the oned being used by the OP. I'm looking for more torque to the rear in addition to using the TRE rear diff upgrade...obviously to help the car have throttle oversteer instead of just pushing wide...in tarmac, no dirt for me.

 

Dave,
If you purchased something like the GEMS unit, the base group N gravel maps should be better than the Ralliart K2 controller. You could then fine tune from there. I'm sure they probably could get you some Group A maps as well, which would be closer to your powerband.
-Bill

 

Would you happen to know of any other shops besides Cascade who would offer tuneable ACD units in the US? I have no issues buying anything from Cascade, I just like to have options to choose between. FWIW, Cascade can supply different maps for the GEMS (~$450ish each), and they can source the Ralliart K2 ACD ECU (~$1200). One thing I haven't asked is how many programs you can store in the GEMS unit.

I did some reading up on the MOTEC yesterday, and with that system, you can setup 4 programs, and there are two default programs to use as well, one with 0% lock, and one with 100% lock. The 100% lock function is particurlarly helpful, b/c if you break an axle, you lock things up and you can limp the car back to service by sending power to the other ends of the car. What I'm not sure of is if there are any companies in the US who can sell me pre-done maps, and at this stage, I'm not sure I want to develop multiple maps from scratch. I've found two shops that sell the MOTEC unit, one is ~$1700, the other about $1850.

Dave