Just ordered kit. What about Torsen Diff ?

[DamnYankee]

Just ordered my kit. Will ship around Oct 1st. Plan is for an LS3 with T56.

This will be my third FFR kit - did a Roadster in 2010 and a 35 Truck in 2018.

I want to have IRS with a 3.55 Torsen diff. But the FFR supplied diff is a TrakLoc. For those who went Torsen, what's the best way to do this?

Thanks, Ron

[JimStone]

I got a salvaged 3.73 Torsen diff from a mustang on eBay. Had around 15k miles. $850. I cleaned it up, put new seals and bearings, but was practically brand new looking with no rust.

I'm doing the same LS3/T56 combo

[Alan_C]

Torsen diffs are available on Ebay, the 3.55 ratio can be found but in shorter supply. I would buy the diff pumpkin online used rather than from FFR. Just my plan as I have ordered a coupe for delivery in September.
Most of the performance ratio differential are iron, heavier but more robust. Not a big weight savings and sometimes a bit more weight at the rear makes balancing the front to rear weight balance a bit easier.

[Jim1855]

I had Forte build an aluminum, Torsen T2, 3.31 IRS for me. This weighed 82#. My car, purchased unassembled, came with an iron 3.55, Traction-Loc weighing 100#. An iron, T2, 3.73 weighs 105#.

I've run a T2 / 3.27 in the older IRS center section and liked it. Probably started with a Traction-Loc. Was 20 years ago and couldn't make an accurate comparison but the gear change from 3.73 to 3.27 was great so I'm doing the same thing, or close, for this build.

I am not remotely concerned about the strength of the aluminum case.

Jim

[edwardb]

I installed a new 3.73 Torsen pumpkin in my Coupe. Ford Performance used to sell them and I think I got one of the last ones. When no one else had any, found Summit had two on the shelf at their Nevada location. I grabbed it and the other one was gone the same day. My previous Roadster was also IRS but with the standard Trac-Lok setup. I'm just a street cruiser and it's a little hard to directly compare the Roadster to the Coupe. The extra wheelbase matters. But for me, the Torsen feels more planted. I don't get any "wiggle" when losing traction like the Roadster did. I'd use Torsen again without question. The only downside is it's a little noisy. Especially with it right next to you in these builds. The Mustang guys mention this too. But they're a little more isolated. I don't pay any attention to it. Just part of the car.

Now that they're no longer new in the aftermarket, you have two choices. Find a good one out of salvage. They're available in 3.73 like mine and also 3.55. The other option is to retrofit one into a Trac-Lok pumpkin. But the new Torsen internals are costly.

[Its Bruce]

I combined a brand new Torsen diff with brand new FRPP 3.55's with rebuild kit, brand new FRPP IRS girdle and a pick-and-pulled aluminum 8.8 IRS center section. This was my first differential build and it's quiet and hasn't grenaded on me. I recommend buying new on the diff itself because I don't trust people. Everything else is pretty dumb iron.

[Skuzzy]

I used the FF supplied cast iron pumpkin and went with 3.31 gears and "peregrine" torsen unit (https://torsen.com/product/ford-super-8-8/), which is stronger than the OEM unit Ford originally used. I paid pros to install it. They liked it.

[DamnYankee]

Thanks everyone for all the info !!!

[Kbl7td]

3.55 with an LS, lots more useable torque down low. You’ll have better cruising RPM at 70+

[Alan_C]

For my coupe, I plan on a late model LT. I too like the 3.55 ratio especially with the 10R80 I want to run. I was thinking the 3.31 would also be a good choice until I learned that the Torsen was not available with a ratio less than 3.55 unless you build your own.

[Skuzzy]

For my coupe, I plan on a late model LT. I too like the 3.55 ratio especially with the 10R80 I want to run. I was thinking the 3.31 would also be a good choice until I learned that the Torsen was not available with a ratio less than 3.55 unless you build your own.

NOTE: I am unclear when you say "build your own" so take the following with the intent it is meant. Just making sure it is clear a taller gear than 3.55 is available.

I am running 3.31 gears with a Torsen unit. Not the original Ford OEM Torsen unit. FF has been shipping the 2015 (and later) pumpkin, which allows 3.31 with a Torsen (34 spline axles) to work. The earlier pumpkins may not (31 spline), but I am not absolute on this point. You can get 3.15 gears for the Super 8 pumpkin and a Torsen now. When I bought my unit the 3.31 gears was the tallest supported.

Then again, if you are running a pre-2015 pumpkin, I will defer to your knowledge about that as I have never researched any differential prior to 2015.


With a 10R80 or a T56, I think 3.55 is a great choice. With a TKX I like the 3.31 gears and a wide ratio TKX.

I wanted to go with an Eaton unit, as I prefer the torque bias of the Eaton units, but Eaton was back ordered and I waited for nine months, but ended up cancelling the order and going with a Torsen unit.

[Alan_C]

NOTE: I am unclear when you say "build your own" so take the following with the intent it is meant. Just making sure it is clear a taller gear than 3.55 is available.

I am running 3.31 gears with a Torsen unit. Not the original Ford OEM Torsen unit. FF has been shipping the 2015 (and later) pumpkin, which allows 3.31 with a Torsen (34 spline axles) to work. The earlier pumpkins may not (31 spline), but I am not absolute on this point. You can get 3.15 gears for the Super 8 pumpkin and a Torsen now. When I bought my unit the 3.31 gears was the tallest supported.

Then again, if you are running a pre-2015 pumpkin, I will defer to your knowledge about that as I have never researched any differential prior to 2015.


With a 10R80 or a T56, I think 3.55 is a great choice. With a TKX I like the 3.31 gears and a wide ratio TKX.

I wanted to go with an Eaton unit, as I prefer the torque bias of the Eaton units, but Eaton was back ordered and I waited for nine months, but ended up cancelling the order and going with a Torsen unit.

To clarify what I meant by build your own, you want something not originally sourced from Ford in the Mustang GT. So you can buy a 3.31 diff and upgrade it to a Torsen, or my preference a Detroit TrueTrac. Or you can buy a Torsen equipped diff with a 3.55 or 3.73 ratio and change the gearing to 3.31 or other.

[Skuzzy]

To clarify what I meant by build your own, you want something not originally sourced from Ford in the Mustang GT. So you can buy a 3.31 diff and upgrade it to a Torsen, or my preference a Detroit TrueTrac. Or you can buy a Torsen equipped diff with a 3.55 or 3.73 ratio and change the gearing to 3.31 or other.

I thought that is what you meant. I got carried away. It happens.

I also prefer the Truetrac, and I waited nine months on backorder before I gave up on it. One of my main objections to the Torsen is they were weaker than the Eaton/Detroit Truetrac, but then this new Torsen is supposed to alleviate that concern. Still, I like the torque bias of the Eaton/Detroit units better.