Advantage of a V8 Torsen rear differential ?

[macspring]

What’s the advantage of installing a V8 rear torsen diff into a C4 urS6 saloon and / or a B4 S2 Avant ?


Is it hard to do, is it worthwhile, and which cars do they come out of ?

If someone posts the definitive answers, this could be a Sticky for others ?

Thanks.

[Error404]

There are quite a few threads on this mate. The Torsens only came in the V8, both auto and manual can be used (mine came out of an auto car).
I think the entire diff from a V8 will bolt up to a URs4 but don't quote me on it. On the B3/B3 chassis you have to fit the V8 diff into the original casing, swapping the crown wheel over. You also have to use both V8 output flanges. Bit of a lottery as to whether you need to adjust the bearing pre-load and backlash, but certainly needs cheecking.

Advantages I have noted as pretty considerable. The on-power blance of the car is very neutral, from default understeer you can control the car on the throttle and get it sideways if you provoke it. Traction is much improved, expcially on corner exit you can get on the gas earlier without spinning up the inside front wheel, instead of scrubbing wide it hooks up and goes.

Disadvantages are they are not as strong as the rest of the drivetrain, launches will kill them and they generate a lot of heat so need good oil and regular changes. IMHO they really need a diff oil cooler if you drive hard or on track a lot.

[UrS4boy]

What’s the advantage of installing a V8 rear torsen diff into a C4 urS6 saloon and / or a B4 S2 Avant ?.

Can't speak to the B4 as to weather the Type 44 V8 torsen rear diff will work or not (might have to have the guts installed into the B4 case, don't know). As for the C4 UrS, it is a straight swap.

The V8 torsen rear diff is NOT a locker, it is a torque-sensing (Tor-sen) rear diff that, in theory, transfers torque automatically and mechanically to the rear wheel with the most grip, up to the mechanical limitations of the diff. In theory, if one wheel starts to slip, the Torsen diff transfers torque away from that wheel and to the other wheel. Its main advantage would be for tracking the car where it would be possible to get an inside wheel spinning when putting down power (i.e. WOT) coming out of a corner.

Disadvantages include fragility, i.e. not good for drag racing = blow up under high RPM clutch drops (maybe not the first one, but soon). Debateable in the snow. The OE UrS4/early non-EDL UrS6 lockable rear diff is probably better if stuck in the snow but again debateable.

I have two uninstalled V8 rear diffs in my garage. Still debating.

For a more academic discussion, see the attached pdf

[caterpillar]

The v8 diffcasing with thorsen will fit right spot on in; audi 100/audi200/urs4/urs6 to 1997(last year for the c4 chassi).. the flence for the propshaft may be changed; but its done in 5min

[UrS4boy]

...Traction is much improved, expcially on corner exit you can get on the gas earlier without spinning up the inside front wheel, instead of scrubbing wide it hooks up and goes....

Inside FRONT wheel?

[A1QSHIP]

On my URS6 with Electronic Locking Differential (applies the rear brake to the spinning rear wheel) I have a V8 rear differential with the torsen fitted. Power On out of low speed corners is fantastic. I had an opportunity to track the car at Putnam Park (http://putnampark.com) Turn 7 was a blast as the rear inner tends to get a little light. No wheelspin, just go. Looking to modify the center torsen for more torque bias to the rear of the car next. In the snow it is very tractable.

[Error404]

Inside FRONT wheel?

Try it

[driftin jo]

Inside FRONT wheel?

Yes, because more grip at the rear due to the torsen means the centre torsen will
transfer more torque to the rear, thus front inside wheel with open diff has less
chance of spinning.

[Error404]

normally on corner exit and on the gas the inside front starts to spins up, the centre diff diverts torque to the rear axle, then the inside rear starts to spin up and you end up with both inside wheels loosing traction and drift wide. With the rear Torsen, as Jo says the centre diff finds what it is looking for from the rear axle and consequently the inside front break traction far less, meaning you can hold a tighter line and get on the gas earlier

[Rusty]

Does the extra grip at the rear push the front wide, like it dies on a rwd car?

[quattro84]

The front inner wheel spins first because it's the wheel with the lowest tyre load. That's how the TorSen diffs work, looking for the path with the least resistance.
I totally agree about the cooling part, a friend had one gone within 3 laps on a dirt track due to the increased power >300kW and wheelspin, it yammed and cracked the entire housing, still drove like stink.

[ralleyquattro]

I prefer locker in the back, forces the back end to slide out and allow you to "powerslide" the car killing understeer completely (at least with torsen centre). My $0.02

[UrS4boy]

Does the extra grip at the rear push the front wide, like it dies on a rwd car?

Thanks jo and error, I buy your explanation, which, should therefore, put power to the outside rear wheel which *should* push the car around the corner in a tight line, i.e. the front should NOT go wide.

I believe they used to call this the "unfair advantage" of quattro.

(Yes, I know the race cars used different diffs)

[pasbogdan]

The torsen starts to deliver torque to the wheel that will spin easyer.It is a little better than an open diff because the transfer is not instant.A torsen on rear should get a little more torque on the rear outside wheel.
This being done(rear inside wheel not loosing traction) the rear part of the central torsen will be "harder" to spin so it will get more torque to the front part of the torsen so to the front diff.

[andy10v]

Relatively easy to fit, found in the Audi V8 only.

Fitting to a B4 S2 avant involves fitting the torsen diff into your s2 casing, and swap the crown wheels then check bearing preload and lash.

Fitting to a URS4/6 should be plug and play I beleive.

I personally like it, its good fun, car balances nicely on the throttle, can progressively control power slides easily. In the rain can drift from 30mph up to 70 on the throttle so smoothly out a corner, notice a big difference getting on the throttle out of hairpins, the car seem to just rocket forward.

Disadvantages are you lose the locking diff if you use it, ie snow etc. It is a Torsen diff, so goes open when you lift a wheel, this is one thing I find annoying on a few corners; uphill hairpin results in lifting the inside rear, and the car slows right down, wheel spins up, hits the deck and the car takes off again ( stock open read diff does this as wel though).

They apparently brake under drag launches with more power, mine has lasted 5 clutch sidesteps at the 1/4, couple at 7000rpm, a couple at 4-5000rpm, chipped 3b plus 75shot off nos being used as the clutch bit. I dont launch my car the rest of the time, occasionally sharp take off, it will do lovely 90* slides if requested.

The Torsen sticky thread

http://www.s2forum.com/forum/showthread.php?t=9680&highlight=v8+torsen

A wavetrack centre and rear would be nice, but rather pricey, as are traditional LSD for out cars