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Budgeting for a new differential this year, need some opinions.

16
11
Exp. Type
Autocross
Exp. Level
3-5 Years
South Plainfield, NJ
Hey guys, I'm budgeting needing a differential at some point this year. I'm on a stock GT Trac-loc diff that was rebuilt by Ford 5 years ago, but started getting into autocrossing and bought some RE71R's last year. So far I'm on 3 autocross events and 4 track sprint events (point A to B on a track, almost an in between of autox and track day). I know I'm gonna need a diff sooner or later.
I'm doing my research and just deciding if I want an Eaton Tru-Trac or Torsen, and which Torsen to get if I go that route (I know theres a few options).
I know there are probably a bunch of threads on this, but would rather get opinions suited to my set up.
I most use the car for weekend drives, autocross events, sprints and looking to try some track days this year.

Appreciate any help on this, I'd rather hear from people who have experience.
 
16
11
Exp. Type
Autocross
Exp. Level
3-5 Years
South Plainfield, NJ
I think if you go to motoiq.com and read the article from @BillyJRacing you will find what you need. He addresses differentials in his right up. And I thought it was pretty informative especially coming from a guy who has won championships in our chassis
Yes I did see that article. I'm leaning a bit toward Tru Trac at the moment, but I just wanted to see if a Torsen T2R would offer anything better based on my application.
 
55
70
Exp. Type
Time Attack
Exp. Level
10-20 Years
Cumming, Georgia
Torsen T2R all the way! There's a reason why Ford Performance OEM'd in in the Boss 302, the PP optioned cars, and the GT350. The continual torque biasing effectively acts like a mechanical version of the fancy electronic vectoring diffs on so many highline performance cars. The more you lean on it in a corner (Up to a point), the more torque goes to the outside wheel effectively helping to steer the car around the corner. It's especially noticeable in the GT350. It took at least .5 second of my lap time at Road Atlanta in "The Beast" during my TT days. I've had real good luck with mine, no downside and it's even reasonably priced from Ford and other places
 

racer47

Still winning after 30+ years
318
368
Exp. Type
W2W Racing
Exp. Level
20+ Years
SE WI
The Eaton Truetrac does everything the torsen does but at a lower cost and with higher durability. I've had several including the one in my current s197. All of them worked perfectly. Autox starts with a launch from a dead stop. Thats when you want the Eatons durability. Torsens can break during hard launches.
 

Grant 302

basic and well known psychic
Torsens can break during hard launches.

Lol. Because you broke them personally? What’s that about regurgitating hearsay? 😁

Mine and many others have held up to hard launches even on slicks. But what do I know, I actually have a Torsen. 🙄

I suggest staying away from the older T-2 and T-2Rs. The newer ones developed for and after the Boss aren’t the same, and I’ve posted lots about the differences in the past.
 
I went with the Eaton and it's been fantastic for me. I believe the bias was between the stock Boss Torsen and the T2R. Traction is excellent. Billy J said he puts them in all his personal cars....even his wife's! It was less expensive than the T2R but that was just a bonus. I think they are both excellent units so you can't go wrong with either.
 

Dave_W

Cones - not just for ice cream
268
267
Exp. Type
Autocross
Exp. Level
20+ Years
Connecticut
Autox starts with a launch from a dead stop.
ProSolo starts are pretty much a drag launch (complete with Christmas tree), but "regular" autocross starts generally are not, though local course designers differ. Nationals courses always have a moderately tight 90 between the start line and the start beam so you don't need to dump the clutch.

One of my data log math channels is absolute right vs left rear wheel speed, and I've seen (and felt) inside rear wheel spin on a medium (for a/x) sweeper at Solo Nats slow my acceleration on corner exit. Concrete surface, '13 Boss in F-Street trim - factory stock with OEM Boss Torsen, softer Strano rear bar, 285-wide RE-71Rs. For autocross, the higher torque bias ratio of the FR500S T2R makes sense. For road courses, the lower TBR of the Boss Torsen or Eaton Truetrac is probably a better choice.
 
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My Trac-Loc started getting weak before the end of my first autocross season in the car. I went with the Eaton TrueTrac based on the recommendation of folks here and elsewhere, combined with the cost.

For my use case (2011 Mustang GT in CAM-C, 285 RE71's), it just flat works. Mine does have a light rattle due to gear lash when costing at low speeds, which seems to be hit-or-miss with the Eaton diff. It is not objectionable to me now that I know what it is...
 
16
11
Exp. Type
Autocross
Exp. Level
3-5 Years
South Plainfield, NJ
My Trac-Loc started getting weak before the end of my first autocross season in the car. I went with the Eaton TrueTrac based on the recommendation of folks here and elsewhere, combined with the cost.

For my use case (2011 Mustang GT in CAM-C, 285 RE71's), it just flat works. Mine does have a light rattle due to gear lash when costing at low speeds, which seems to be hit-or-miss with the Eaton diff. It is not objectionable to me now that I know what it is...
Good to know. I'm also running RE71's, but square 275/35 set up. I'm running no rear sway bar at the moment to help give the diff some give but that probably wont last too much longer.
 
This article should answer all of your questions on the different diff options:

Project Budget 400WHP S197 Mustang Track Car: Part 5 – Upgrading to an Eaton Truetrac LSD


" A performance Limited Slip Differential is a MUST for making 2005-2014 (S197) Mustangs handle predictably. We replace the weak factory LSD with Eaton’s TrueTrac helical (gear-driven) LSD which will transform the driving experience and character of the car.

000 COVER Eaton TrueTrac-X2.jpg

In the article:
-Stock LSD vs Torsen-style
-The tech behind Torque Bias Ratios
-Installation


-Billy
 
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Torsen T2R all the way! There's a reason why Ford Performance OEM'd in in the Boss 302, the PP optioned cars, and the GT350. The continual torque biasing effectively acts like a mechanical version of the fancy electronic vectoring diffs on so many highline performance cars. The more you lean on it in a corner (Up to a point), the more torque goes to the outside wheel effectively helping to steer the car around the corner. It's especially noticeable in the GT350. It took at least .5 second of my lap time at Road Atlanta in "The Beast" during my TT days. I've had real good luck with mine, no downside and it's even reasonably priced from Ford and other places
The T-2R was not used on the BOSS 302 street car or the BOSS 302S race car, nor the GT350. Torsens don't 'vector' the torque or provide any of the significant benefits that e-diffs are able to do. Torsens have a Torque Bias Ratio, which is the maximum distribution of torque from one side to another. Multiplying the tractive ability of the (inside) tire with less grip by the TBR will give you the total amount of grip the LSD can send to the outside tire. So the more you 'lean on it in a corner', the more you unload the inside tire, and thus, REDUCE the amount of torque that goes to the outside tire.
 
I like the Torsens, but there is another option, you can rebuild the ford limited slip unit with carbon discs I'd expense is an issue.

From my article above:

"
The factory Ford “Traction-Lok” Limited Slip Differential (LSD) is sufficient for the stock power level when new, but they don’t hold up well to track use or more power. They are not very durable and tend to wear out quickly, reducing the amount of lock and making the car handle worse.

The amount of ‘lock’ is determined by a series of clutch plates that are squeezed together and preloaded by a bent metal “Z-spring” in the center of the diff. Increasing the pre-load and friction with an aftermarket spring and clutch plates will increase the static lock and holding ability of the diff. This is fine for drag racing but is really bad for handling because it increases understeer by resisting the different wheel speeds required for turning in the middle of a corner. To make Mustangs turn, you do not want any drag or lock from the LSD mid-corner when off the throttle."
 

Dave_W

Cones - not just for ice cream
268
267
Exp. Type
Autocross
Exp. Level
20+ Years
Connecticut
I'm probably going to change my '13 Boss Torsen to a T2R for the higher TBR for autocross use, but I've also got my eye on the Moser Wavetrac. Helical-gear LSD like a Torsen, but with an extra component to generate pre-load when the wheels are turning different speeds. That way, you still get torque to the wheel with traction even if the other wheel is completely unloaded. Only problem is, there's no direct fitment.
 

racer47

Still winning after 30+ years
318
368
Exp. Type
W2W Racing
Exp. Level
20+ Years
SE WI
I'm probably going to change my '13 Boss Torsen to a T2R for the higher TBR for autocross use, but I've also got my eye on the Moser Wavetrac.....

You could try changing the rear end oil first and see if it helps. Having real data is very nice!!

I run 85w140 conventional in my Eaton. I don't have any inside wheel spin problems. At least none that I can feel. I don't have any data but I do have A7s and a lot of power. Eaton used to recommend heavy weight conventional gear oil for greater bias. It may help with the torsen too.

Also there are other brands similar to wavetrac. They are popular in oval track racing where they are called 1/4 tight or 1/2 tight as the preload goes up. But finding an 8.8" version may be difficult.
 
3,315
3,069
From my article above:

"
The factory Ford “Traction-Lok” Limited Slip Differential (LSD) is sufficient for the stock power level when new, but they don’t hold up well to track use or more power. They are not very durable and tend to wear out quickly, reducing the amount of lock and making the car handle worse.

The amount of ‘lock’ is determined by a series of clutch plates that are squeezed together and preloaded by a bent metal “Z-spring” in the center of the diff. Increasing the pre-load and friction with an aftermarket spring and clutch plates will increase the static lock and holding ability of the diff. This is fine for drag racing but is really bad for handling because it increases understeer by resisting the different wheel speeds required for turning in the middle of a corner. To make Mustangs turn, you do not want any drag or lock from the LSD mid-corner when off the throttle."


If expense is an issue
freely admit it's not optimum
 
55
70
Exp. Type
Time Attack
Exp. Level
10-20 Years
Cumming, Georgia
The T-2R was not used on the BOSS 302 street car or the BOSS 302S race car, nor the GT350. Torsens don't 'vector' the torque or provide any of the significant benefits that e-diffs are able to do. Torsens have a Torque Bias Ratio, which is the maximum distribution of torque from one side to another. Multiplying the tractive ability of the (inside) tire with less grip by the TBR will give you the total amount of grip the LSD can send to the outside tire. So the more you 'lean on it in a corner', the more you unload the inside tire, and thus, REDUCE the amount of torque that goes to the outside tire.
Quote: "By tuning and managing that friction level across the performance range, the differential has the ability to support imbalances in traction, allowing the tire with better traction to receive more torque while preventing unwanted wheel spin. The differential’s ability to bias more torque to the tire with better traction is characterized as the Torque Bias Ratio, or “TBR” for short. This essentially represents the ratio of high traction to low traction that the differential can allow while remaining locked. The higher the TBR setting, the more aggressive the traction performance is"

The "Wheel with better traction that receives more torque" IS the outside wheel. More torque to the outside wheel = vectoring "away" from the outside wheel thus helping to steer the car around the corner. Both the Boss and GT350 use a Torsen diff.

 
There's a lot of misunderstanding of how torsens function. They do not vector the torque.

A 3.0:1 TBR does not mean the outside tire is being driven 3X as fast. Think of it as the inside tires grip determines the overall grip and acceleration of the car.

If the inside tire can generate 0.3 Gs of acceleration before slipping, the outside tire will be sent 3X that amount of torque, or 0.9 GS (assuming the tire has that grip). For simiplicitys sake and the sake of understanding (at the cost of some accuracy) assume the car accelerates at 0.9 GS because the outside tire is the most heavily loaded tire and determines the majority of the cars acceleration.

Now let's say you're in the rain, and the inside tire only has 0.1 Gs of grip. The Torsen will only deliver 0.3 Gs of grip before the inside tire lights up and spins. So due to the overall decrease in grip, limited by the inside tires total tractive force, the car in this occasion will only accelerate at 0.3 Gs before lighting the inside tire up with wheel spin. The car accelerates at 1/3 the rate as the first example because the inside tires grip was reduced to 1/3.
 

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