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Discussion Starter #1
I've looked, and haven't really found any good info regarding DCCD, VCD/TC and road racing in STis. I might have missed it, and if so sorry about that. But what I'd like to know is what settings people have found to work for them in road racing, like at Willow Springs or Buttonwillow, etc.

Like VDC and TC all the way off (orange)? Or in sport mode (green)? DCCD on auto, or all the way rear biased (65r/35f I think)? Or somewhere in between? I know some of it is going to come down to personal preference, just wondering what people like. I've done a decent amount of road racing, but never in an STi, or any car that I've been able to control the center diff and traction control.

I used to road race Sentra SE-Rs, and my built one had a Quaife mechanical LSD which was absolutely awesome. It dug into corners similarly to the way the STi does. Now that I have the STi I've sort of been hankering to get back into it.
 

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I've looked, and haven't really found any good info regarding DCCD, VCD/TC and road racing in STis. I might have missed it, and if so sorry about that. But what I'd like to know is what settings people have found to work for them in road racing, like at Willow Springs or Buttonwillow, etc.

Like VDC and TC all the way off (orange)? Or in sport mode (green)? DCCD on auto, or all the way rear biased (65r/35f I think)? Or somewhere in between? I know some of it is going to come down to personal preference, just wondering what people like. I've done a decent amount of road racing, but never in an STi, or any car that I've been able to control the center diff and traction control.

I used to road race Sentra SE-Rs, and my built one had a Quaife mechanical LSD which was absolutely awesome. It dug into corners similarly to the way the STi does. Now that I have the STi I've sort of been hankering to get back into it.
Subaru uses Torsen diffs which act more like open diffs, so don't be fouled because these can't be compared with the Quaife diff. If you really want your Subaru to turn in then have your front diff changed. You can make it turn by trail braking but this is not a very good idea for street driving and also with the e-brake but the stock STI has a lot of understeer. You have to get used to it before you will be able to drive it to its potential.

Regarding traction control and VDC, these are off when the light is orange. When is green you only have the TC off and the VDC will be more permisive. I would suggest to got with the all off (orange) option after you start learning how to drive this car.

Regarding DCCD use it on Auto- when you have good grip and Auto+ when you have less grip. If you want to be in control then change it in manual and go to the bottom on dry surfaces with good grip and upper when is slippery. Don't lock the diff only on snow or ice or you could damage the center diff...
 

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What is the point of locking the diff if not to use on snow or ice?

Snow or ice should give way for the wheels to slip if they need to.

Full lock when you do have grip causes things to bind?
 

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If you are on a road track there should be no difference between vdc green and vdc amber cause you should never activate the vdc. The TC on these cars is imo pretty scary if you are driving hard, but green or amber should make no difference.

diff should be run in auto imo as it is really a best of both worlds type scenario where you get less front drive preapex when you are working to turn the car and more post apex to suck it though.

+/neutral/- settings imo should be used as another front to rear biasing tool like f/r camber ratio, f/r tire pressure ratio, or f/r sway bar ratio. It makes a big difference in that way to help dial in the car and its super easy to adjust while you are driving to find what is best relative to that day, track surface and temp, and all the rest of your settings that cannot be adjusted while you are moving.
 

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I can see it happening in a track situation. VDC will use the brakes to make up for the front and rear diffs acting like open diffs when without any traction or to prevent them from being over run. I haven't seen it happen, but it's certainly possible.
 

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Subaru uses Torsen diffs which act more like open diffs, so don't be fouled because these can't be compared with the Quaife diff.
Torsen and Quaife make the same kind of LSD, typically called a helical or automatic torque-biasing LSD. They should behave almost identically in any given application. (Except for the Torsen T-3, which the STI does not come with.)
 

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Discussion Starter #9
Yeah, I don't have any knowledge of the diffs Subaru uses, all I can say for sure is that when the STi digs into a corner I can feel the diffs working in the same way my SE-R's Quaife did. It's an odd, almost physics-defying sensation. I could go full throttle in first gear around a corner and not break the front tires loose, it was great.

In the STi when I have the vdc on green, I can get into a corner and when the front diff starts working I can get light oversteer, and just glide through onramps with the tail hanging slightly out. It's pretty awesome.

Thanks for the collected info. I'm looking forward to getting my car onto a road course at some point, this will all help.
 

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I cannot speak for anything other than the DCCD, but if a road course, leave it set to auto. The computer can think/react faster than you and having the variability is an excellent bonus when trying to reach 10/10's. At some point I hope to have empirical data to support this.
 

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Couldn't really help but to notice all of you have GR series STIs... Does the DCCD work the same in the GD and GR series? What about the diffs?

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Couldn't really help but to notice all of you have GR series STIs... Does the DCCD work the same in the GD and GR series? What about the diffs?

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<----- GD Series, 2007. IIRC, the DCCD is the same and as are the diffs, for the most part.
 

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Couldn't really help but to notice all of you have GR series STIs... Does the DCCD work the same in the GD and GR series? What about the diffs?
It's not just about GR vs GD, it's about the exact model year. Subaru made some kind of diff and DCCD logic change in every year from 2004-2008. (They may have made DCCD logic changes in 2009-2011 too, but they haven't published anything to that effect.)

USDM mechanical differentials by model year:

Front diff:
2004: AP Suretrac-brand cam-based LSD (acts like a helical/Torsen/Quaife gear-based LSD, but uses cams instead of gears for friction; I've read that they're less smooth than most helical LSD's, but I'm not sure how their performance compares)
2005-2011: helical gear-based LSD

Center diff:
2004-2005: 35/65 front/rear torque split planetary center diff + DCCD electro-mechanical clutch for up to 100% lockup
2006-2011: 41/59 front/rear torque split planetary center diff with limited mechanical LSD functionality (advertised as providing up to 35% lockup) + DCCD electro-mechanical clutch for up to 100% lockup

Rear diff:
2004-2006: clutch-based LSD
2007-2011: Torsen-brand helical gear-based LSD

That list just covers the mechanical bits. The DCCD controller has gained more sensors, more auto modes, and overall better auto logic over the years. The two biggest changes were the addition of the Steering Angle Sensor (SAS) in 2006, and the Auto+ and Auto- modes in 2008. There were other auto mode logic changes throughout the GD years however.

Also the earlier transmissions had a pump for lubrication, whereas the later ones rely on the gears flinging oil around, as nearly every road car transmission does. I *think* Subaru made the switch mid model year 2006 or mid 2007, but I don't remember for sure.

Got it? :D
 

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That's some decent info there.

Do you have any clue what EUDM 2008 year has included? Also which brand front diff is?

CHeers,
Ales
 

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The helical front LSD isn't branded, i.e. it's just a Subaru part. I doubt Subaru themselves manufacturers it, but it's probably built by a company that only supplies OEMs, not a company with an aftermarket lineup like Torsen, Quaife, etc.

As far as EDM or any non-USDM goes I have no idea, sorry. Have you checked your local Subaru subsidiary's website for STI specifications?
 
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