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E46 Xi Forum
The E46 XI was produced from 01-05 in sedan and touring body styles. Powered by either a 2.5L inline 6 in the 325xi or a 3.0L inline 6 330xi. Discuss all thing about BMW AWD E46 'Xi' here.

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Old 06-09-2011, 10:47 AM   #21
TiAgXi
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I suppose DSC could correct the issue by applying the brakes. That just seems like a terrible system to me..
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Old 06-09-2011, 11:49 AM   #22
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This is why, from my understanding, the transfer case is NOT an open diff, and if a LSD is installed in the rear, the transfer case will NOT send power to the front wheel that has the least amount of traction, rendering the rear LSD useless. To the contrary, I think that the system will continue to send power to the rears to let the diff help sort it out without the use of DSC. Either way, a WaveTrac is on my next to-do after my Dr. Vanos visit Saturday, and the Dynavin install in a month.
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Old 06-09-2011, 12:04 PM   #23
SamDoe1
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Originally Posted by TiAgXi View Post
I suppose DSC could correct the issue by applying the brakes. That just seems like a terrible system to me..
I had DSC off when I was stuck last winter. Both axles were spinning wheels.
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Old 06-09-2011, 01:34 PM   #24
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Originally Posted by SamDoe1 View Post
I had DSC off when I was stuck last winter. Both axles were spinning wheels.
On the XI, DSC is never completely OFF.

On the XI, all you are turning off is the stability portion of the software. The e-diff portion of the software is still active and will always be active, no way to shut that off. Meaning, 100% of the time the software is running that will electronically modulates brakes to 'simulate' a limited slip.
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Old 06-09-2011, 02:28 PM   #25
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On the XI, DSC is never completely OFF.

On the XI, all you are turning off is the stability portion of the software. The e-diff portion of the software is still active and will always be active, no way to shut that off. Meaning, 100% of the time the software is running that will electronically modulates brakes to 'simulate' a limited slip.
Does that still use the ABS system to brake the wheels then? Cause when I turn mine off by pushing the button on the dash, the ABS no longer pulses at all when in low grip situations. I know when it's working with DSC on but I don't notice the same going on when I have it off.
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Old 06-09-2011, 02:49 PM   #26
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Does that still use the ABS system to brake the wheels then? Cause when I turn mine off by pushing the button on the dash, the ABS no longer pulses at all when in low grip situations. I know when it's working with DSC on but I don't notice the same going on when I have it off.
The owners manual says that "The Automatic Differential Brake (ADB-X) enhances traction in critical situations (such as those encountered on snow-covered roads) by using selective braking intervention to replace the limited-slip functions executed by the differential and transfer case in conventional drivetrains." Page 75 (emphasis added).

Perhaps it is "open" and I was right about the brakes keeping any axle from losing power...
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Old 06-09-2011, 03:52 PM   #27
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Remember. When there is no slip, the system does send the power to all wheels. This is important. It doesn't 'try' to break one wheel loose. That would only happen if one wheel had very little traction AND the other three were stuck like glue. It would almost never happen with the vehicle rolling. The initial setup is pretty potent.

If that one wheel does slip, the traction control brakes only that wheel shooting power to the other three (first and strongest to the other rear and then to the fronts). Easy correction.

It is not that the AWD is a cheap afterthought and an inferior system. It's that we BMW drivers expect RWD like handling. We want our cars to oversteer. We want to be able to break the rears loose a little bit. We want an early indication of 'starting to break loose'. We want to feel and experience the road.

I have a friend with a new WRX who says the handling in his car is a bit 'boring' because it absolutely just goes where he steers it. He has no warning when he is pushing it too hard. Where are the upper limits of his car's handling? He will never know until he suddenly flips over and starts rolling.

To be frank, most of the people complaining about the traction control are really mad at the DSC. They just don't understand the system well enough to know that DSC is the culprit. Traction control does not cut the throttle. That is the real let down.

Does anybody still disagree with the following statement?
"The xi transfer case is 'open' but not balanced. It splits torque when there is traction. It is constantly engaged."

Last edited by karatechop5000; 06-10-2011 at 01:07 AM. Reason: punctuation
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Old 06-09-2011, 04:10 PM   #28
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This is why, from my understanding, the transfer case is NOT an open diff, and if a LSD is installed in the rear, the transfer case will NOT send power to the front wheel that has the least amount of traction, rendering the rear LSD useless.
I would not say useless at all. Some fine points of the chassis dynamics may be altered; but you will have a theoretical improvement overall. You will spend a buttload of money and carry some extra weight. Like I said on your thread. I would consider if I had more money. I think the payoff is much more noticable upgrading an open RWD car to limited slip.
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Old 06-09-2011, 11:53 PM   #29
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Originally Posted by karatechop5000 View Post
Remember. When there is no slip, the system does send the power to all wheels. This is important. It doesn't 'try' to break one wheel loose. That would only happen if one wheel had very little traction AND the other three were stuck like glue. It would almost never happen with the vehicle rolling. The initial setup is pretty potent.

If that one wheel does slip, the traction control brakes only that wheel shooting power to the other three (first and strongest to the other rear and then to the fronts). Easy correction.

It is not that the AWD is a cheap afterthought and an inferior system. It's that we BMW drivers expect RWD like handling. We want our cars to oversteer. We want to be able to break the rears loose a little bit. We want an early indication of 'starting to break loose'. We want to feel and experience the road.

I have a friend with a new WRX who says the handling in his car is a bit 'boring' because it absolutely just goes where he steers it. He has no warning when he is pushing it too hard. Where are the upper limits of his cars handling? He will never know until he suddenly flips over and starts rolling.

To be frank, most of the people complaining about the traction control are really mad at the DSC. They just don't understand the system well enough to know that DSC is the culprit. Traction control does not cut the throttle. That is the real let down.

Does anybody still disagree with the following statement?
"The xi transfer case is 'open' but not balanced. It splits torque when there is traction. It is constantly engaged."
I think I agree with everything you just posted.
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Old 06-10-2011, 09:11 AM   #30
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Originally Posted by karatechop5000 View Post
I have a friend with a new WRX who says the handling in his car is a bit 'boring' because it absolutely just goes where he steers it. He has no warning when he is pushing it too hard. Where are the upper limits of his car's handling? He will never know until he suddenly flips over and starts rolling.
I disagree with this. Depending on the year of WRX, the older ones had no stability control, open front, viscous center, viscous rear. Newer ones, open front/rear, viscous center and ESC. I've never felt any WRX that had "boring" handling, and the steering provides plenty of feedback. If he has no warning when pushing it too hard, it's likely because A) He's a poor driver, or B) He's on stock tires. More likely A. The WRX's handling limits aren't too difficult to approach; it's not an invincible car, and it's definitely one that provides feedback. Not sure where this comes from.

Further, the STi and all new automatic Subarus do, in fact, have a RWD bias. 35/65 and 41/59 on the STis and 40/60 on the automatics.

Back on topic, the XI handles incredibly well with its current setup, but like most cars, a better suspension/bars/tires and a real LSD can all help make it that much better.
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Old 06-10-2011, 10:11 AM   #31
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I doubt I would be bored either. Even if the handling was neutral, the power to weight ratio would be a blast.
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Old 06-10-2011, 11:00 AM   #32
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I thought new STi's had a torsen rear and some other kind of LSD center (vc, i think).
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Old 06-10-2011, 11:07 AM   #33
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I thought new STi's had a torsen rear and some other kind of LSD center (vc, i think).
I was referring to the WRX. The new STis have a helical (torsen-like) front, torsen rear, and planetary computer controlled Driver Controlled Center Differential. The bias varies depending on the year, but it can send up to 100% of the power to either axle. The DCCD I've got on my Forester STi is managed using an aftermarket computer that uses an accelerometer and throttle feedback to determine where to send torque while in auto mode. The controller also allows the center diff to be locked to distribute torque evenly between the two axles regardless of split.
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Old 06-10-2011, 11:23 AM   #34
TiAgXi
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...on my Forester STi ...
LOL talk about a q-ship
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Old 06-10-2011, 11:29 AM   #35
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LOL talk about a q-ship
Yep...it's not my daily (The 330xi is) - Love both of 'em. The FSTi is a killer sleeper though. 360WHP on a Mustang Dyno, about that much torque.

Some pics:
http://www.flickr.com/photos/gsloan/4914720358/
http://www.flickr.com/photos/gsloan/4087480996/
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Old 06-10-2011, 11:39 AM   #36
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Ummm. What's a 'q-ship'?
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Old 06-10-2011, 12:22 PM   #37
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A q-ship was a WWII german warship disguised as a merchant ship. they looked harmless but carried serious firepower. in the context of cars the term is used to describe an ordinary looking car that because of mods is really fast. basically, it's the same thing as a "sleeper."

edit: i guess they weren't german... british and american
http://en.wikipedia.org/wiki/Q-ship

Last edited by TiAgXi; 06-10-2011 at 12:28 PM.
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Old 06-10-2011, 03:33 PM   #38
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OK. Thanks for the definition. Thanks everyone who took the time here. Thanks for the documentation and for the experiment/video. I feel like I have a 'grip' on this topic. Get it?

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Old 06-10-2011, 03:38 PM   #39
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Yep. Agreed that an LSD will help a RWD BMW out more than an AWD one, but it will certainly benefit our cars, since all of the power will not go out a slipping front wheel.
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Old 06-10-2011, 04:00 PM   #40
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Wait, so the final determination is that the the transfer case is essentially an open differential?
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