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View Full Version : All you ever wanted to know about ACD



earlyapex
12-19-2005, 03:27 PM
http://www.norcalmotorsports.org/users/bryan/mods/EVO/ACD.pdf

enjoy.

Cameron@xperformance
12-19-2005, 10:17 PM
nice! i just wish i could understand it all

cerebus
12-19-2005, 11:22 PM
There was a link to this in a previous thread about ACD mods and how the ACD works. What's interesting about this article is that it claims that for best cornering performance, the front/rear split should be 30/70 and that a 50/50 split gives the best traction performance and stability. (middle of section 2.1) Front/rear weight split doesn't seem to have been considered or wasn't considered a factor in arriving at these conclusions.

Mitsubishi chose the 50/50 split for stability and traction, and use the ACD to affect steering response (end of section 2.1) and use the AYC to optimize cornering performance.(end of section 4)

So how does the lack of AYC affect our cars? How much are we losing in handling performance compared to the rest-of-world Evo's?

Also, they assume that a rigid 4WD system gives the best performance and I wonder if that's the best assumption to make.

And does anyone know the conversion from Nm to ft/lbs? In section 2.2, the article discusses why they chose a center diff that could limit torque to 2000 Nm.

That other thread had some other links as well that need to be investigated. This is hard stuff to understand!

earlyapex
12-19-2005, 11:47 PM
2000 Nm = 1475 ft-lb

All the UK track whores get rid of the AYC after it breaks. They all say the earlier RS version was the best version for track, which is basically the same stats as our 04 RS (non-acd and AYC but with LSD)

That is why I always laugh when all the evom.net kiddies grab their weeniers for AYC.

SouthBayGSR
12-20-2005, 11:46 AM
I don't think the lack of AYC makes too much of a difference with ACD & LSD present. Though optimally having both would seem to have the greatest effect. ACD shifts torque from back/front while yaw control shifts left/right (only rear tires, correct?). AYC is just a more powerful and computerized LSD. You gain much more with the ACD system in all around traction, especially under rapid transitions as I believe the ACD system has the ability to become near-open differential.

Overall interesting article. It also explains a little more on the reasoning on the user controlled- gravel, tarmac, snow settings for baseline torque splits.

This also makes me want to read up on Subaru's AWD system. The STi relies on more of a (cockpit controlled) locked F/R ratio, correct? I think this is what sets these two cars apart in driving characteristics with the evo's nimbleness in the ACD, and the STi's I'm staying sideways with all the torque in the rear attitude.

earlyapex
12-20-2005, 12:35 PM
You are correct AYC only controls left and right torque dist in the rear.

The STi DCCD can be run in full auto mode which works much like our ACD. The DCCD can also be run in full manual mode where you can specify bias more middle or rear, or full lock and it will move from open diff to that depending on slippage. Which is why if set to 35:65 (open diff) you can do big boy powerslides. I believe the 06 sti actually has an even more rear biased setting feature, I think 30:70. Keep in mind, no matter where you set the DCCD, it will run in 35:65 open diff mode until it senses slippage.

In summary, the DCCD is much like our ACD, Torque split is always open diff (35f/65r in the sti) regardless of DCCD setting. It's really how much it actually locks up during normal driving conditions. Alot of people think that DCCD controls the amount of torque when it's really how much it actually locks up during normal driving conditions. Sounds alot like our ACD eh?

here is a good DCCD writeup:
http://wallace.as.arizona.edu/~cgroppi/DCCD_FAQ/DCCD_FAQ.html

turbotiger
12-20-2005, 12:38 PM
Have you seen the Best Motoring video that showcased the 05 Evo MR in japan? They compared a stock 05 MR with the updated for 05 Super AYC (more torque transfer) with a Group N RS evo rally car (Only the RS is group N certified)

They mentioned the hinderance of the earlier AYC and tested the newer for 05 AYC, and considered it alot better. They then drove the 05 MR and the Group N RS evo rally car (with modifed ACD) on the track and contributed to the faster speed and easier handling to the new AYC which the RS lacked.

redvolution
12-20-2005, 02:59 PM
http://www.roadandtrack.com/article.asp?section_id=31&article_id=2908

The video from this article mentions that only now (for '06) does Subaru use a yaw-sensor input to DCCD.

That's one area where the ACD previously held a big advantage over the DCCD.

dohcvtec
12-20-2005, 03:37 PM
I could have sworn the 05 STi also had yaw-sensor input for the DCCD.

turbotiger
12-21-2005, 01:42 PM
I thought it was the steering angle sensor that was new for the STI's

earlyapex
12-21-2005, 01:45 PM
05 STi did have yaw sensor input as well as steering angle, braking, etc much like the ACD has.

SouthBayGSR
12-21-2005, 11:30 PM
good info Apex. Good article too. Now that I look at it, the DCCD and the ACD are basically the same with a few minor variations. The STi is built at a main 65:35 open and a 50:50 open for the evo. Both have user-alterable settings. The evo article made an interesting comment of why they made the torque split user-settable rather than relying on inconsistant and possibly troublesome sensors to do so. Looks Like Subaru and Mitsu both agreed on this, yet dont agree on a standard bias!

cerebus
12-22-2005, 08:52 PM
Hi folks:
FYI
EvoM has a sticky up about the ACD as well.