Discussion on the best rear differential for an all out road race car? Torsion, clutch, locker?

[darkostoj]

We converted a 1977 Rolls Royce into an all out race car and we are having a problem getting traction in the corner exit and trying to figure out what to do in terms of the diff.

It has a 9" axle with a fully adjustable 3 link and we can't get the inside rear wheel to stop spinning on corner exit no matter what we do. We have tried jacking up the anti squat until we get too much brake dive in corners, removed rear sway bar, and softer springs. I think the only thing left for us to try is swapping out the diff.

It currently has a wavetrac torsen type diff.

So what are the advantages and disadvantages of

1. Torsen Diff
2. Clutch Diff
3. Locking Diff (like detroit locker)

Are there any other styles I'm missing?

Would be nice to get a discussion going on the pro's/con's of each

[Matt@BOS]

Despite what people trying to sell you Wavetracs will say, they are very easy to kill especially when autocrossing and depending on car setup, probably road racing as well.

If you have a lot of adjustability in the rear suspension, and it sounds like you do, then you'd probably be happiest with a clutch type or Torsen style. If you need to run a rear sway bar, then I'd go clutch style, and if you can skip the way bar and get all of your roll stiffness from the rear springs and roll center height, then I'd get a Torsen style diff like true trac. The latter style sort of just feels like it does its own thing, because it torque biases, and doesn't require tuning of its own, so you set the suspension up around it. On the other hand, if you get an clutch style diff from OS Giken, they will set the diff up around the car.

Matt

[darkostoj]

Originally Posted by Matt@BOS

Despite what people trying to sell you Wavetracs will say, they are very easy to kill especially when autocrossing and depending on car setup, probably road racing as well.

If you have a lot of adjustability in the rear suspension, and it sounds like you do, then you'd probably be happiest with a clutch type or Torsen style. If you need to run a rear sway bar, then I'd go clutch style, and if you can skip the way bar and get all of your roll stiffness from the rear springs and roll center height, then I'd get a Torsen style diff like true trac. The latter style sort of just feels like it does its own thing, because it torque biases, and doesn't require tuning of its own, so you set the suspension up around it. On the other hand, if you get an clutch style diff from OS Giken, they will set the diff up around the car.

Matt

What is the difference between a wavetrac and a torsen style diff?

[Che70velle]

Is it only spinning the inside tire, or does it get the car loose on exit by spinning both eventually?
I had a similar problem once with an older chassis that I had when I raced asphalt late models. My problem wasn’t so much spinning the inside tire, but the car was loose on exit...due to inside tire spin, therefore causing locker to lock and get me loose...and we tried everything. I’m talking we threw the notebook at the car, and could not get it right. Changed rears. Messed with stagger from 0 to 4+”, sway bars, springs, shock settings, moved weight, new tires, old tires, wheel offsets, you name it. We couldn’t fix it. Finally figured out it was unloading inside tire because rear shock mounts were wrong, causing the shock to be too short, therefore lifting the tire effectively. Ran a 9” stroke shock package, just as the chassis manufacturer suggested. Had to change upper shock mount on chassis to fix. About drove me crazy. Especially considering that I have all of the computer simulator software that is available at the time and it’s telling me I’m not loose. My setup guy and shock builder helping me was Chase Elliots crew chief for his super late model stuff, and he told me to junk the car and buy a new one, which I about did. But I’m persistent and we finally figured it out.

[darkostoj]

Originally Posted by Che70velle

Is it only spinning the inside tire, or does it get the car loose on exit by spinning both eventually?
I had a similar problem once with an older chassis that I had when I raced asphalt late models. My problem wasn’t so much spinning the inside tire, but the car was loose on exit...due to inside tire spin, therefore causing locker to lock and get me loose...and we tried everything. I’m talking we threw the notebook at the car, and could not get it right. Changed rears. Messed with stagger from 0 to 4+”, sway bars, springs, shock settings, moved weight, new tires, old tires, wheel offsets, you name it. We couldn’t fix it. Finally figured out it was unloading inside tire because rear shock mounts were wrong, causing the shock to be too short, therefore lifting the tire effectively. Ran a 9” stroke shock package, just as the chassis manufacturer suggested. Had to change upper shock mount on chassis to fix. About drove me crazy. Especially considering that I have all of the computer simulator software that is available at the time and it’s telling me I’m not loose. My setup guy and shock builder helping me was Chase Elliots crew chief for his super late model stuff, and he told me to junk the car and buy a new one, which I about did. But I’m persistent and we finally figured it out.

Oh wow, that is a problem that would drive someone absolutely crazy. I don't think we have that issue but I'm going to double check now!

[Matt@BOS]

Originally Posted by darkostoj

What is the difference between a wavetrac and a torsen style diff?

Both of them are torque biasing differentials, but I don't know enough about wavetracs to comment the mechanical differences, aside from the fact that Wavetracs were designed to work in zero, or near zero load situations, whereas truetracs were not designed with that in mind, which is why they can spin the inside tire like an open diff.

I'm not sure how easily it is to dig up the info via the search function on the forum, but I know there have been posts about wavetracs over the years from a number of individuals who broke either broke theirs, or were trying to figure out if they had broken one. In some instances, I know they tend to feel like an open diff when they go out. Nick Relampagos with the Speedtech sponsored 2nd gen Camaro was having issues putting power down, and once swapping to a truetrac, the issue went away!

[dontlifttoshift]

The helix on the gears in a wavetrac isn't steep(?) enough so the bias ratio isn't very high.......and they aren't very durable.

A torsen T2r for late model mustang 8.8s has an advertised bias ration of 4:1 if I remember right. The True Trac is 3:1 in the same application....again, going off memory. The bias ratio for the same diff in different manufacturers housings can vary.

I wish Strange would do the S Trac in a 31 spline version. That thing is bullet proof. Call them and ask for it. I asked at PRI but I am not sure anyone was listening.

Tim McGilton was trying a new diff but I can't remember what it was.