Torsen vs standard Traction lok LSD differential pros and cons?

[Elp_jc]

The Torsen in the Bullitt is my first, and during aggressive canyon carving, it feels better in every respect than the many clutch-type LSD's I've had. And I'm very happy with it. But maybe on a track, it's not as nice, as some of you reported. By the way, what's the bias ratio on the 3.73 Torsen on the Bullitt? Just curious. Thanks.

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[ice445]

The Torsen in the Bullitt is my first, and during aggressive canyon carving, it feels better in every respect than the many clutch-type LSD's I've had. And I'm very happy with it. But maybe on a track, it's not as nice, as some of you reported. By the way, what's the bias ratio on the 3.73 Torsen on the Bullitt? Just curious. Thanks.

Its the same as the rest of the units. You can increase the bias ratio by swapping the gear oil and not using the friction modifier. I guess Ford put it in to make the Torsen have better street manners.

 

[Brian@BMVK]

The Torsen in the Bullitt is my first, and during aggressive canyon carving, it feels better in every respect than the many clutch-type LSD's I've had. And I'm very happy with it. But maybe on a track, it's not as nice, as some of you reported. By the way, what's the bias ratio on the 3.73 Torsen on the Bullitt? Just curious. Thanks.

2.8:1 as shipped

 

[Vlad Soare]

That's exactly the kind of abuse that wears the clutches or cones out in those styles of limited slip diffs in track driving. Just that you may not be pushing as much power through everything as you would while racing or driving at near race-pace at HPDE on the track, so wear rates would tend to be somewhat lower.

Trac-loc and similar limited slip diffs can also cause increased rear tire wear rates if there's much bias. The force required to make the limited amount of slip happen and permit normal cornering ultimately comes from increased longitudinal contact patch forces.

I understand that, and I'm OK with it. If that's the price for having fun with the car, so be it.
Of course, it's a matter of degree. If this style of driving wears out the clutches in the diff in, say, five thousand miles, then I won't be happy, and I will probably look into installing a Torsen. But if I get, say, fifty thousand miles out of them, as opposed to a hundred thousand miles driving like a granny, then I won't mind, and I will just replace the clutches when the time comes.

 

[WD Pro]

Hi @Brian@BMVK - this caught my attention :

2.8:1 as shipped

As it may help me find an answer to a question I asked on this thread : https://www.mustang6g.com/forums/threads/wavetrac-differential-technical-info-for-gt.43397/

Sorry for the long quote, but after reading this :

Only in general terms, as I have never had a Wavetrac in my hands to study it closely. On a very basic, fundamental level, they are both the same class of product - a parallel-axis, helical-gear differential. Beyond that, there are a lot noticeable and more subtle differences.

The biggest is that Wavetrac adds the mechanism to the center that is intended to provide some lockup when one tire is completely unloaded. I can't attest to its effectiveness, though I have no doubt that Wavetrac will tell you it works well. It at least looks clever. I'm not sure how it comes into play when both outputs are loaded, especially when transitioning between operating modes, or what it does when supporting side gear thrust-in loads. If it does what it is supposed to do, then it is a neat trick indeed.

Once past that, the most significant difference is the layout of the actual gear package. Wavetrac's design appears to mesh the element gear pairs together in the center, and each meshes with a side gear on the outboard ends. This is similar to Quaife, GKN, etc. A Torsen T-2 rearranges that somewhat, giving the element gears two or three mesh transfers, with the side gear mesh in the middle. This is done to balance the tipping load on the gear, which in turn reduces the PV loading on the gear bore in the differential housing. It reduces that load enough that housing no longer needs to be made of steel to withstand the load. Instead, ductile iron is perfectly reasonable. The tradeoff is somewhat less overall friction, and lower locking effect. Torsen can make up the friction elsewhere, however, and is very tunable for locking effect. The other drawback to the Torsen arrangement is that it requires more axial space to package. Fortunately, the Super 8.8 has axial length in spades.

If we look at the gearing itself, it is a matter of gear geometry, material, face width and number of element gears in the system that determine locking performance and strength. I know that the Torsen is tuned to exactly what performance characteristics that Ford vehicle dynamics wanted (the PP diff is tuned for autocross and open track use, whereas the GT350 Torsen is strictly tuned for track use). I also know that the differential far exceeds the strength requirements as set down by Ford. Impact testing has typically required multiple axle shafts to finish because the spline shaft snaps off the CV tulip. OTOH, I can't comment at all about Wavetrac's design targets for either criteria; they may well be stronger, but I have no idea what their design bogies were. They do use a more premium alloy for gear steel (9310). Although this adds cost, it does improve overall toughness and is less prone to crack. 9310 is often used in gearing when the torque requirement has outstripped your ability to add mesh length, or the geometry is fixed, but you need more out of it.

Locking performance is more subjective to use and need. If I were guessing, I think that their torque bias ratio (TBR is the metric in which locking effect is quantified) is probably fairly similar in drive mode to the Torsen, but higher in the coast mode (coast mode TBR was kept low on the S550 Torsen to improve turn-in). That is, however, a guess based on general experience with that gear configuration - I will reiterate that I've never had their part in front of me to compare. Perhaps Wavetrac will tell you what their product's TBR values are.

I asked this :

This is real interesting info and has raised a few questions that I hope you can answer

A) You mention that the PP and GT350 Torsens are set up differently, what handling traits vary based on which setup is selected ?

B) If you bought a Torsen from Ford Performance (only one part number), do you get the PP or GT350 setup ?

Any info would be really appreciated

Cheers,

WD

I never got an answer. What are your thoughts on that (the part about ford using different configurations on the Torsen) ?

Cheers,

WD

 

[Brian@BMVK]

Hi @Brian@BMVK - this caught my attention :



As it may help me find an answer to a question I asked on this thread : https://www.mustang6g.com/forums/threads/wavetrac-differential-technical-info-for-gt.43397/

Sorry for the long quote, but after reading this :



I asked this :



I never got an answer. What are your thoughts on that (the part about ford using different configurations on the Torsen) ?

Cheers,

WD

Both are T2R units, and I'd guess the difference in TBR is down to the fluid fill and modifier (or lack thereof). I have a GT350 diff in mine with the 75W90 BG oil w/ friction modifier. It works very well for open track and autocross.

 

[WD Pro]

Both are T2R units, and I'd guess the difference in TBR is down to the fluid fill and modifier (or lack thereof). I have a GT350 diff in mine with the 75W90 BG oil w/ friction modifier. It works very well for open track and autocross.

Thank you

I know my inquisitiveness is going to get the better of me - I will have to hunt down the specs for the different models now and see if Ford messed around with what they filled them with ... lol

I am only interested as I have a new FP Torsen sat in the garage and at some point I will have to decide what I should fill it with.

WD

 

[Vlad Soare]

Can a friction modifier affect the TBR of a Torsen? I thought the TBR depended only on the angle of the gears and couldn't be changed.

 

[Norm Peterson]

Can a friction modifier affect the TBR of a Torsen? I thought the TBR depended only on the angle of the gears and couldn't be changed.

I'm pretty sure that there is a small effect. Don't know how much.


Norm

 

[DB83]

So the friction modifier would make the Torsen more aggressive? or less?

 

[Brian@BMVK]

So the friction modifier would make the Torsen more aggressive? or less?

Less. About 5-10% less TBR. Going up to the 75W140 from 75W90 has about a 10% reduction in TBR also.

 

[shogun32]

Less. About 5-10% less TBR. Going up to the 75W140 from 75W90 has about a 10% reduction in TBR also.

man, I must not understand Torsen at all! Or all those YT videos showing the workings are missing something big - how gears that mesh or spin somehow change their lockup points based on lubricity? Or is there a 'silent' clutch pack in there?

I thought that TrakLoc had both a 'breakaway' torque figure (inter-plate friction from preload) and also once the 2 axles were sufficiently out of sync a ramp that forcibly clamped the clutch plates together far, far beyond the spring preload numbers and converted the axle to be just like the S197 solid live axle.

 

[Brian@BMVK]

man, I must not understand Torsen at all! Or all those YT videos showing the workings are missing something big - how gears that mesh or spin somehow change their lockup points based on lubricity? Or is there a 'silent' clutch pack in there?

I thought that TrakLoc had both a 'breakaway' torque figure (inter-plate friction from preload) and also once the 2 axles were sufficiently out of sync a ramp that forcibly clamped the clutch plates together far, far beyond the spring preload numbers and converted the axle to be just like the S197 solid live axle.

Friction is friction.

https://torsen.com/how-it-works/

 

[K4fxd]

I think the Detroit tru-trak has clutches. It will drive with one wheel in the air unlike the torsen.

 

[TeeLew]

man, I must not understand Torsen at all! Or all those YT videos showing the workings are missing something big - how gears that mesh or spin somehow change their lockup points based on lubricity? Or is there a 'silent' clutch pack in there?

You might just be visualizing its action incorrectly. It doesn't have a lock-up point, so that's one thing. The TBR is the friction created by trying to transmit power through a worm gear. Worm gears work great on the 'drive' side, but they're inefficient when being driven by a spur gear. This inefficiency creates the friction which drives the outside tire. Anything which lowers the internal friction in the diff will reduce the amount of side-to-side torque transfer available (i.e. a lower TRB).

This gives some good info with lots of pictures:

https://www.kmpdrivetrain.com/differentials/plated-limited-slip-differential-explained/

https://www.kmpdrivetrain.com/differentials/torsen-vs-plated-limited-slip-differential/

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