Alright, so the '05 Evos are out now. I assume they have a hydraulic pump for locking the center diff, so can this pump be used for a S-AYC rear diff as well?

I know all the necessary sensors are there (lateral/longitudinal g sensors, steering angle sensor, etc). If there is hydraulic pressure for the rear diff, I assume all one would need would be the electronic signal to control it, correct? Or do the JDM/UK/Aussy/Everywhere else Evos have 2 hydraulic pumps? I am hoping the Evo IX will have S-AYC, but if it doesn't, I definitely want to convert it. I am just planning ahead.

 

Well, in short, no. The S-AYC uses dual clutch packs to transfer torque left/right and has a separate reservoir for the S-AYC fluid, which has to be replaced every couple thousand miles. Also, the AYC takes up a lot of space and cars that have it require a smaller fuel tank without the US required evaporative emissions equipment. If I were to guess, it would still be a lot, even if you could retain the sensors it would seem that there is some significant hardware that would have to go on. The Evo IX makes its debut in April, so it's not too long until we'll find out what it'll have. If you must have S-AYC, then definitely wait to see if it's an option, but my guess that retrofitting it to any current USDM evo would be highly cost prohibitive, particularly when there are so many options for improving the handling of your car via wheels/tires/suspension.

 

I know it transfers torque left & right, that's why I want it. What exactly is S-AYC fluid and why would it be different from the active center diff fluid?
I thought the emissions stuff is under the hood, and the UK/JDM versions of the Evo have a 55 liter capacity (55 liters = 14.53 gallons, same as ours).
April for USDM or JDM/UK?

 

I cannot wait untill AYC is on USDM Evo so everyone will stop wanting it so bad. The system isnt all that great but they will soon learn

 

Yeah I like to learn my lessons the hard way

 

The main thing I don't like about my Evo's handling is that it won't pull me out of tight turns very well, and just plows when it's on power spinning the inside front wheel. A front LSD, active center diff, and a rear diff trying to rotate my car sounds great to me!

 

I dont think you will ever be able to find that perfect medium for Evo handling. 4WD cars either push alot or oversteer. After all it is a "rally" car. If I could give my AYC I would. As soon as mine blows I will not be looking back.

 

From what I've heard, the S-AYC is light years ahead of the AYC on your VI though.

 

If it is I hope they work on the reliability of the system.

 

The emissions equipment I'm talking about is for the evaporative emissions on the fuel tank, which is in the rear. One major reason the AYC is different from the ACD is that the ACD has a single clutch pack that locks the differential, forcing a 50/50 torque split in the event that the rears are slipping or are likely to slip. So essentially you have 100/0 front/rear to 50/50 front/rear. AT NO TIME is greater than 50% of torque diverted to the rear.

ACD is simple in comparison to AYC which is symmetrical and can divert greater than 50% of the torque to either side. Two do this you need twice the clutch packs and you have a much smaller amount of space to do it. Combined with the fact that AYC is varying lockup much faster and more often (basically whenever you turn) means that the duty cycles are also harder on the clutch packs. This translates to a different fluid that needs to be changed more often.

I would abandon my dream of AYC. It would JUST NOT be possible. You'd be better off waiting for it to come to the USA (and it might not, because it's really not that great) and trading in your car. Or just learn how to drive better so you don't rely so much on driver aids.

 

Although the 05 EVO doesn't have the AYC, IMO the ACD and helical diff in the front do a nice job of pulling the car out of a corner compared to others cars I've owned/driven with open front diffs and viscous center diffs (03-04 EVO, WRX, DSM).
Link at this diagram: though it talks about AYC also, you can see how the ACD is opened in the turn, so that the rear tires have no power and cannot push the car into understeer, at this time the front end is "pulling" the car through the turn with the help of the helical front diff.

 

If you notice, step 3 is where the AYC is really working, which is precisely the point I am talking about coming out of a turn under power. Seems like the extra rotation would be great.

 

All that crap for a car is just to much...the car is smarter than the driver LOL

 

you could do donuts easier with the active yaw control. lol

i think it could be a over kill for a daily driver, unless you live in seattle where it rains all the time.

 

I live in Portland where it rains all the time, but I'm talking about track days. At the end of the front straight at PIR there is this chicane 90 degree right then about 120 degree left (like a U-turn) and coming out of that left, my left wheel is squeeling, i'm off/on the throttle trying to get the jump out of there, and it feels like i'm just stuck in quicksand. It's frustrating.