Stasis 4:1 Center Diff Questions...

[SullyS4]

For those who have done this mod or are familiar with it...a few questions:

1. Can you feel the difference on the street during sporty driving?

2. Would you buy it again?

3. Any downsides to the 4:1 vs. 2:1 bias?

4. Where to buy it for best price? Got quoted $550 from SPP and direct from Stasis.

Thanks guys

[Alipor]

You might want to ask Jet/Jockey this question he has it on his A4 along with the LSD he did a write up about it a while back. You might want to search for that.

[belinko]

Have you spoke with Jeremy at Matrix or in the suspension brake forum hosted by Matrix?

Here's a link to a Thread where we talked about the LSD's and diffs. I would also do search in the forums.

http://www.audizine.com/forum/showth...threadid=81905

[Alex@STaSIS]

Howdy! This is Alex over at Stasis, just joined into this community and I can surely answer any questions you have.

I run one of these 4:1 Torsen Center Diffs in my '01 S4, only chipped in terms of power upgrades. I could tell an immeadiate difference coming out of the apex of a corner hard. Audis tend to understeer power on, the great thing about the 4:1 center is that when understeer starts to occur the differential has the ability to transfer more power from the front to the rear, 4:1 ratio, versus the stock 2:1 ratio. So in these situations the Torsen will get more power to the back end of the car to help neutral it out. Now let's say you get the car to step out on power the 4:1 center will allow more power to be transferred up front and it will essentially pull the front end which makes the rear end follow, like a FWD car. As I like to describe it, the 4:1 Torsen Center is like having Quattro Plus, it enhances the quattro in a great manner and it's a relatively cheap modification for what it does.

Now it works with all your factory ESP and ABS, it won't cause them to behave oddly in any way.

There is really no downside, there are no ill effects, there are no compromises, honestly it's one of the upgrades on a driveline that has no downside. That's coming from me as a user, not as a salesman

You can come right to us for $550, you send in your unit, we modify it that day or the next and out it goes back to you!

If you have any questions don't hesitate to email or call!

[jeremy@matrix]

Originally posted by belinko
Have you spoke with Jeremy at Matrix or in the suspension brake forum hosted by Matrix?

Here's a link to a Thread where we talked about the LSD's and diffs. I would also do search in the forums.

http://www.audizine.com/forum/showth...threadid=81905

Thanks for the recommendation.

We <heart> STaSIS center diffs.
No sales tax in OR either.

[Jedi-Jurist]

Jeremy:

What would getting the center diff w/o the rear clutch type diff do for (or against) you? I, like everyone else, want to elimanate the understeer and induce some oversteer when desired.

P.S. You can ignore my post in the other forum.

P.P.S. It's been more than a week since your ride was taken, so it wasn't Overhaulin'. Any leads? I can't believe it was taken right out from under you.

[jeremy@matrix]

Originally posted by Jedi-Jurist
Jeremy:

What would getting the center diff w/o the rear clutch type diff do for (or against) you? I, like everyone else, want to elimanate the understeer and induce some oversteer when desired.

P.S. You can ignore my post in the other forum.

P.P.S. It's been more than a week since your ride was taken, so it wasn't Overhaulin'. Any leads? I can't believe it was taken right out from under you.

Alex details a very good description above.

Many of our clients start with the center diff and then add the rear. The center diff (in a 410whp C5 A6 2.7T w/ Ohlins and race tires) is incredible on track. Back end steps out then front pulls. It's seamless.

PPS---The B5 S4 was found the day after it was stolen, 1/2mi from the house. Two perps were seen running from it after they couldn't get it into reverse and rear ended an X5. K9 and forensics were called but the prints didn't lead to anyone. :(

[belinko]

Why wouldn't you be able to get the car into reverse? Why did they rear end an X5, I don't get it?

[jeremy@matrix]

Originally posted by belinko
Why wouldn't you be able to get the car into reverse? Why did they rear end an X5, I don't get it?

Car has a SSK so the shifter is notchy. The clutch is also an aftermarket unit so it's grabby. If you don't know a German car, you would look at the 6spd knob and think that you can just push the knob to the left and up for reverse right?(of course you have to push down but some thiefs apparently don't know this).

So, they must have pushed the knob to the left and up (in 1st gear), let the clutch out (clutch pops out quick), rear ending the X5 they were parked behind. They both flee/run and a friend's father-in-law who lives nearby who was just happening to be driving home sees the whole thing unfold. Calls me for the plate number, BINGO. They block off the entire neighborhood, call K9 and forensics.

<SORRY FOR TAKING THIS OFF TOPIC!>

[Spidee]

This diff is another reason I would consider getting an S4 or RS4.

[Jrunr]

Anyone else purchase a center dif and want to post their results and/or observations?

[Silver streak]

For those who have done this mod or are familiar with it...a few questions:

1. Can you feel the difference on the street during sporty driving?

2. Would you buy it again?

3. Any downsides to the 4:1 vs. 2:1 bias?

4. Where to buy it for best price? Got quoted $550 from SPP and direct from Stasis.

Thanks guys

1) yes 100%
2)yes 100%
3)no
4)I bought mine on line from stasis, the core charge is a bitch but I did get my money back.

The biggest difference I notice is at the track on exiting corners, a little more ass happy.

[Jrunr]

Does it help your 0-60 at all? Or is it more of a "handling" modification?

[Silver streak]

If there is any difference it is not noticeable. I mean we have 4 wheel drive, dump the clutch and your gone whether its 2:1 or a 4:1 center diff. I do notice more rear wheel spin when launching and you would think there would be more weight in the rear, hence better take off?

I know our cars are heavier in the front but when you launch weight gets transferred to the rear as it takes off.

[markbradford]

The core charge isn't a bitch on the B6/B7 S4s cause it's not an option. Stasis doesn't have any cores for us. :-/ I'd much rather pay the refundable $550 than have downtime for my car, as I don't have a garage space for a disabled car. This fact alone has kept me from getting the high bias center diff. Bummer...

[bsrpilot44]

The core charge isn't a bitch on the B6/B7 S4s cause it's not an option. Stasis doesn't have any cores for us. :-/ I'd much rather pay the refundable $550 than have downtime for my car, as I don't have a garage space for a disabled car. This fact alone has kept me from getting the high bias center diff. Bummer...

big 2nd...help us out Stasis

Make it work and ill order it tmm...if i have no downtime :)

[[email protected]]

1) yes
2) yes and I wish I bought it a lot earlier
3) no
4) purchased and installed by Matrix

If you drive a lot in the rain like I do the car feels a lot more solid as well. On the drive home from Portland I was driving through a rainstorm and the car felt like it was driving on dry pavement.

[Jrunr]

Does it help your 0-60 at all? Or is it more of a "handling" modification?

[markbradford]

Does it help your 0-60 at all? Or is it more of a "handling" modification?

It helps whenever there's a shortage of traction in the front and torque must be transferred to the rear. In a stock B6/B7 S4, there's not really enough power to be all that concerned about a straight-line 0-60 run IMHO. I doubt it would do much - if anything maybe a tenth of a second.

However, when you're turning and XX% of the tire's traction is already being spent on the lateral forces involved with turning, there's a greater chance that you will not be able to efficiently put down the minimum 33% engine power that the stock Quattro system sends to the front wheels. In this case, having the high bias center diff will allow you to transfer more power to the rear, improving acceleration.

Bottom line: If you had 500hp and fat R-compound tires, then yes, the diff would likely help substantially when it comes to 0-60 times. In stock form, probably not.

But really though - if you were concerned about 0-60 times, why buy a 3800+ pound car?

[RAudi Driver]

I wouldn't do a center diff without doing the rear. It can slow down your car by allowing less power to be transmitted to the ground.

Since an open diff always applies the same amount of torque to both wheels you may be at a loss for power going into a turn. If 80% of the power is sent to the rear and one of the wheels can't get traction, the other wheel will be limited in the amount of torque that it can apply to the ground. If almost no torque is required to spin one wheel, the other wheel will get no torque either. Remember, the same amount of torque is applied to both wheels. Your car will be stuck in the hole until both wheels can track again. The rear diff is essential to take advantage of the center diff mod. That being said, this is going to be a $3,500 mod. Quite expensie unless you track the car.

If you need further elaboration, just say so and I'll go into my rant. If you disagree, then state your reasoning.

[markbradford]

Uh, OK, here's my reasoning. It's simply not correct.

Quattro's EDL system uses the ABS sensors to detect wheelspin. When sensed, the caliper applies the brake to the spinning wheel to transfer torque to the other side with grip. As a reactive system, it's not as effective as a true LSD, but it works and has been employed as part of the Quattro system for over a decade.

[markbradford]

Furthermore, since you mention being "stuck in the hole", I'm inferring that you're talking about on-road performance? (In less than optimal conditions obviously).

In cases like this the Torsen center diff would simply end up sending the torque to the front where the grip is. The two rear wheels could be on rollers and the front two would still receive torque to create acceleration.

I'm not sure if you're new to Audis RAudi Driver, but this is not the same as a RWD BMW with an open diff. The same rules of physics apply of course, but are manipulated by several different mechanical systems.

...anyway, bottom line is you do not need the limited slip rear diff for the high bias center diff to be a worthwhile, or cost-efficient modification.

[Jrunr]

Wow. I know I resurected an old post, but I do not want to cause conflict here. My goal is to get a bit of information to educate myself about my S4.

I test drove the new S5 a few weeks ago and I was completely impressed by its off-the-line performance. Afterwords, I did a lot of reading pertaining to the S5 and discovered that the 0-60 time has been rated at almost 5.0 seconds. This caused me to wonder if I could possibly get my car to have the same 0-60 as the S5 and, if it is possible, learn what modifications I need to make to get it there.

I have heard great things about the center dif and its performce on the track, but I am mostly curious to how it will effect my daily driving. I love to drive, and drive hard, so this is where I am going with all of this. I do not do 1/4 racing, but I do love to get on it from a stop, or a freeway on ramp, etc...

Thanks again for your time and help.

[Audii-Dudii]

In cases like this the Torsen center diff would simply end up sending the torque to the front where the grip is. The two rear wheels could be on rollers and the front two would still receive torque to create acceleration.

I'm afraid the above statement is wrong. The Torsen provides a multiple of the torque that can be supported by the end of the car with the least traction to the end of the car with the most traction and as always, anything times zero is ... well, zero. (Yes, there's a very small amount of torque that can be supported due to the friction in the diff's bearings and gears, etc., but it's de minimis and for all practical purposes, rounds to zero.)

Lift a rear wheel under cornering or spin a front wheel under acceleration and with a Torsen center diff and open front and rear diffs, your AWD car will immediately become ZWD (that's Zero-Wheel Drive) until either the wheel drops back to the ground or EDL kicks-in to stop it from spinning. BTDT many, many times with my A4 track car, which is why it now has a modified 944 LSD in the rear diff case.

[Audii-Dudii]

However, when you're turning and XX% of the tire's traction is already being spent on the lateral forces involved with turning, there's a greater chance that you will not be able to efficiently put down the minimum 33% engine power that the stock Quattro system sends to the front wheels. In this case, having the high bias center diff will allow you to transfer more power to the rear, improving acceleration.

There's a misconception that when accelerating hard out of a corner, a higher-bias ratio Torsen will "send" less torque to the front wheels and more torque to the rear wheels than a lower-bias ratio Torsen. This is false.

In fact, it "sends" the same amount of torque to the front wheels but a higher multiple of that torque to the rear wheels. The higher-bias ratio Torsen doesn't transfer any load away from the front wheels to the rear wheels but does take advantage of the rear wheels' underutilized capacity to support torque by allowing the engine to develop more torque overall (which is why the car can accelerate harder) and then allocating all of this additional torque to the rear wheels (which increases their slip angle and makes the car understeer less, improving its cornering performance).

The downside, of course, is that a higher-bias ratio Torsen will "shudder" more when driven around parking lots or parallel parking, etc., which is why Audi chose to compromise between performance and NVH issues by specifiying a lower bias-ratio.

[Silver streak]

quote: ^^^
"The downside, of course, is that a higher-bias ratio Torsen will "shudder" more when driven around parking lots or parallel parking, etc., which is why Audi chose to compromise between performance and NVH issues by specifiying a lower bias-ratio."

You may have this problem because you have the LSD rear end as-well as the 4:1 center diff.? I don't know what your talking about, as I and other people that have this mod have mentioned there is no down side. I live in a high rise and park in P 4, four floors down, no shudder, as smooth as silk. I have had this mod for over a year I think I would of heard or felt something if there was any issues with the 4:1 center diff.

[RAudi Driver]

Uh, OK, here's my reasoning. It's simply not correct.

Quattro's EDL system uses the ABS sensors to detect wheelspin. When sensed, the caliper applies the brake to the spinning wheel to transfer torque to the other side with grip. As a reactive system, it's not as effective as a true LSD, but it works and has been employed as part of the Quattro system for over a decade.

Not trying to argue with you but the EDL doesn't work past 50mph when one would need it the most. In addition, when I want to do some spirited driving the ESP is switched off. I've driven my car where the ESP kicks in and i got to tell you that the car just shuts down till it gets planted again.

[RAudi Driver]

Furthermore, since you mention being "stuck in the hole", I'm inferring that you're talking about on-road performance? (In less than optimal conditions obviously).

In cases like this the Torsen center diff would simply end up sending the torque to the front where the grip is. The two rear wheels could be on rollers and the front two would still receive torque to create acceleration.

I'm not sure if you're new to Audis RAudi Driver, but this is not the same as a RWD BMW with an open diff. The same rules of physics apply of course, but are manipulated by several different mechanical systems.

...anyway, bottom line is you do not need the limited slip rear diff for the high bias center diff to be a worthwhile, or cost-efficient modification.

Alright, here's where your reasoning for this mod goes out the window. Once again, not trying to argue.

What you're saying is that you'll do this mod and when you lose traction to your rear wheels, the power will be sent to the front. If this is the case, why would you do the mod in the first place. Wasn't the intent of this modification to get the power to the rear where traction is greatest on corner exit. If you have rear wheel lift then this mod goes out the window and is useless. You will have no power in the rear. Your power will be limited to the amount that the center diff can allocate to the front and that's not 100% of the cars power.

Do you see why you need to do the rear diff mod with this?

Correct me if I am wrong.

[Audii-Dudii]

You may have this problem because you have the LSD rear end as-well as the 4:1 center diff.? I don't know what your talking about, as I and other people that have this mod have mentioned there is no down side. I live in a high rise and park in P 4, four floors down, no shudder, as smooth as silk. I have had this mod for over a year I think I would of heard or felt something if there was any issues with the 4:1 center diff.

A rear LSD does exacerbate the infamous Torsen "shudder" but certainly isn't the cause of it. The phenonemon is very well documented and a side-effect of the Torsen's basic design. Here's why: The Torsen center diff varies the torque split between the front and rear wheels by limiting the difference in rotational speed between the front and rear driveshafts.

When a car goes around a corner, the front wheels travel a longer distance than the rear wheels. With an AWD car, this requires the front driveshaft to rotate faster than the rear driveshaft. Whereas an open center diff can fully accomodate a difference in the driveshafts' rotational speeds but always splits torque 50-50 between the front and rear wheels, and a locked center diff can't accomodate any difference in rotational speeds but can split torque 100-0-100 and everywhere in between, the Torsen center diff behaves like a hybrid of the two: It's never fully "open" (which is why it can vary the torque split between the front and rear wheels over a limited range) and never fully "locked" (which is why it can accomodate some percentage difference in rotational speeds between the front and rear driveshafts).

The "shudder" people experience when making a tight turn under low power (and the car must be under power because a Torsen diff behaves like an open diff when it's not, which is why it works with ABS and a locked diff doesn't) happens because the Torsen doesn't differeniate at all until the bias-ratio reaches its limit. Read that sentence again, very carefully, as it's critical to understanding exactly how a Torsen does what it does and most people find the Torsen's operation to be counterintuitive (in other words, they assume it behaves like an open diff until it partially locks whereas it actually behaves like a locked diff until it partially opens).

Here's how a Torsen works: Torque from the engine causes the gears inside (half of which are connected to the front driveshaft, half of which are connected to the rear driveshaft, and all of which are in-mesh with each other) to jam together as the front and rear driveshafts attempt to rotate at different speeds, almost -- but not quite -- locking up solid until one of the driveshafts overcomes the gears' resistance to rotation (i.e., the designed bias-ratio is reached) and they begin to rotate at different speeds.

Because the Torsen center diff can accomodate only a limited difference in rotational speed between the two driveshafts (which is how it maintains the torque split at the bias-ratio), the speed at which each wheel is forced to rotate doesn't necessarily match the speed at which it's rolling across the road surface. Of the four, the inside rear wheel travels the shortest distance and is the least heavily loaded; as such, it's generally the wheel that's forced to compensate for the rotational/longitudinal speed mis-match by slipping and/or being dragged across the surface, and it's this that is the cause of the "shudder" many people (but apparently not you) experience. The reason this effect is not more apparent than it is, is because the engine usually isn't making very much torque at these speeds, hence the gears inside the Torsen aren't jammed together very tightly.

That said, there are several reasons why the shudder is more apparent under low power/low speeds than high power/high speeds, the foremost of which is the fact that at low power/low speeds, the car isn't cornering very hard and the load on the inside rear wheel is high because very little of it has been transferred to the other three wheels. Combined with the low power, this means the inside rear tire is dragged more than it slips or spins. Then there's also the fact that at low speeds, the tires' slip angles are generally small and the percentage difference between the average slip angle of the front tires and rear tires is at its greatest. However, as the slip angles increase in response to the increased amount of torque being developed at the tires, the percentage difference between the average slip angle of the front and rear tires decreases, reducing the (effective) difference in the distances traveled by the front and rear wheels and in turn, reducing the rotational/longitudinal speed mismatch at the inside rear wheel/tire that's the cause of the shudder.

To increase the Torsen's bias-ratio -- from the OEM setting of 66-34-66 (~2:1) to say, 80-20-80 (4:1) -- you simply make the gears jam together tighter, increasing the internal friction that resists differentiation, and thus cause it to behave even more like a locked center diff. The tradeoff, though, is that the more you make a Torsen behave like a locked diff -- and this includes performing Stasis' high-bias mod -- the less it behaves like an open diff. In other words, by increasing the bias-ratio, you're also _reducing_ the Torsen's ability to accomodate differences in the rotational speeds of the front and rear driveshafts. [I won't go into it here, but if you think about it, you'll see that, when under power and with all other things being equal, the Torsen biases the torque split to the rear wheels whenever the steering wheel is turned away from straight ahead and toward the front wheels whenever it's turned back ... ponder the implications of how _that_ might affect a car's behavior while going around corners, especially if you also keep the power on by left-foot braking!]

As an aside, it's interesting to note that with its first generation of Torsen-equipped cars (Type 44 chassis), Audi set the bias-ratio at ~3.5:1 (78-22-78) versus the 2:1 that it used with the B5 chassis A4 and S4 models. It's not known whether this reduction in the bias-ratio was done to address NVH issues or performance/safety concerns -- some people believe the higher bias-ratio resulted in quirky handling with the Type 44 chassis under certain conditions (aka as the "Spider Bite" phenomenon) -- but there's no doubt that it did reduce the amount of shuddering people experience.

Anyway, the bottom line is that what you gain on one side of the equation, you lose on the other, and faced with this decision, Audi revised its initial stance with its later cars, and chose to set the Torsen's bias-ratio low enough so that most people never experience any shudder whatsoever, even if that also meant settling for a less than optimal bias-ratio so far as outright performance was concerned.

[Audii-Dudii]

If you have rear wheel lift then this mod goes out the window and is useless. You will have no power in the rear. Your power will be limited to the amount that the center diff can allocate to the front and that's not 100% of the cars power.

Actually, the amount of torque the Torsen center diff can "send" to the front wheels in this situation is its bias-ratio (2:1 or 4:1 or whatever:1) x however much torque is required to spin the inside rear wheel while it's hanging in the air, which isn't very much. In this situation, absent the intercession of EDL (which doesn't respond instantaneously, btw), AWD effectively becomes ZWD and the car will coast until it slows enough for the wheel to drop back to the ground.

Do you see why you need to do the rear diff mod with this?

The reason that a clutch-pack LSD is helpful in this situation (and a Quaife LSD is not) is that it guarantees the Torsen center diff will always experience some resistance to rotation from the rear wheels, so the amount of torque that can be developed at the front wheels is always greater than zero.

[RAudi Driver]

Actually, the amount of torque the Torsen center diff can "send" to the front wheels in this situation is its bias-ratio (2:1 or 4:1 or whatever:1) x however much torque is required to spin the inside rear wheel while it's hanging in the air, which isn't very much. In this situation, absent the intercession of EDL (which doesn't respond instantaneously, btw), AWD effectively becomes ZWD and the car will coast until it slows enough for the wheel to drop back to the ground.



The reason that a clutch-pack LSD is helpful in this situation (and a Quaife LSD is not) is that it guarantees the Torsen center diff will always experience some resistance to rotation from the rear wheels, so the amount of torque that can be developed at the front wheels is always greater than zero.

Nicely put! BTW, I think that Mark bailed from this thread.

[Audii-Dudii]

Nicely put! BTW, I think that Mark bailed from this thread.

Thanks for the kind words. I've been studying the Torsen diff for more than a decade now -- Yes, I'm a veteran of the (in)famous Torsen war that was fought at www.audifans.com nearly a decade ago -- and I have a fairly good understanding about how it works as well its strong and weak points. It's really a very clever design, but it's far from perfect when used in a center-diff application...

[markbradford]

Lift a rear wheel under cornering or spin a front wheel under acceleration and with a Torsen center diff and open front and rear diffs, your AWD car will immediately become ZWD (that's Zero-Wheel Drive) until either the wheel drops back to the ground or EDL kicks-in to stop it from spinning. BTDT many, many times with my A4 track car, which is why it now has a modified 944 LSD in the rear diff case.

BTDT as well on my Stage 3 A4 track car. Specfically, every lap at Blackhawk Farms turn 6.

[markbradford]

Nicely put! BTW, I think that Mark bailed from this thread.

Actually I was helping to feed over 350 homeless people a holiday meal at Truman College all day.

[markbradford]

Not trying to argue with you but the EDL doesn't work past 50mph when one would need it the most. In addition, when I want to do some spirited driving the ESP is switched off. I've driven my car where the ESP kicks in and i got to tell you that the car just shuts down till it gets planted again.

EDL is not part of the ESP system.

ESP will retard ignition and cut fuel to reduce power in addition to braking various brakes to bring the vehicle yaw back in order. The EDL system functions completely separately from the ESP system, and cannot be disengaged except by the computer over 50mph, or if you pull the ABS fuse.

[markbradford]

Alright, here's where your reasoning for this mod goes out the window. Once again, not trying to argue.

What you're saying is that you'll do this mod and when you lose traction to your rear wheels, the power will be sent to the front. If this is the case, why would you do the mod in the first place. Wasn't the intent of this modification to get the power to the rear where traction is greatest on corner exit. If you have rear wheel lift then this mod goes out the window and is useless. You will have no power in the rear. Your power will be limited to the amount that the center diff can allocate to the front and that's not 100% of the cars power.

Do you see why you need to do the rear diff mod with this?

Correct me if I am wrong.

No, my point is that the situation was specious at best.

If your problem is with rear wheel lift then you should address the problem with suspension setup, as you likely have too stiff a rear ARB. A high bias center diff doesn't make you pick up a rear wheel.

[markbradford]

Nicely put!

LOL. His point about "ZWD" basically invalidated your original post.

It doesn't matter if you have the regular diff or a high-bias one - if you have a wheel off the ground, you're going nowhere without EDL's help.

Like I said - wheel lift is a separate problem.

[Cargo8]

sorry. what is EDL?

[markbradford]

sorry. what is EDL?

Electronic Differential Lock. It's been part of the quattro system since the B5 chassis' introduction.

The system uses the ABS sensors to detect wheelspin. When detected, braking force is applied to the spinning wheel. This allows the open diff to put power to the ground again.

[Audii-Dudii]

If your problem is with rear wheel lift then you should address the problem with suspension setup, as you likely have too stiff a rear ARB. A high bias center diff doesn't make you pick up a rear wheel.

The problem that causes the inside rear wheel to lift is a lack of droop travel in the rear suspension, a long-standing issue with Audi's suspension designs. As Mark has pointed out, modifying the center diff will have no effect on this, nor, unfortunately, will decreasing your rear roll couple by softening the rear a/r bar. The B5 chassis, at least -- I haven't had my B6 long enough yet to know whether the same holds true for it or not -- has the potential to lift the inside rear wheel under hard cornering with even with the softest a/r bar Audi installed on the car.

The proper cure is to redesign the rear suspension and/or to install a rear LSD so the car can continue to put power down while the wheel is in the air.