LSDs

[GR40Freak]

I would recommend, if you want to go torque sensing diff, either a Torsen (which have had some reliabilty concerns on later models) or DPI http://www.dpiracingproducts.com/store/rear-ends-service-parts-differentials-c-4_5.html

Not putting down on the tru-trac but I didn't have a good experience with mine. I'm considering a DPI myself but believe you may have to convert to non-c-clip axles with them. And as you can see they're not cheap. Haven't researched it yet.

I use a Torsen T2-R and I love it. The DPI is a fantastic unit and is more suited to higher HP cars. 400RWHP plus. Also DPI have a new 8.8 unit that uses the c-clips so you don't have to change to 9" axle ends.

Colin

 

[Infamousjim]

Where did you get the clutches?

I've got them for $120 shipped. Brand new in the box.

I got em from my ford supplier through the bodyshop i moonlight at, I'd go with 19cobra93's set, that's a good deal.

 

[Gray Ghost GT]

The DPI is a fantastic unit and is more suited to higher HP cars. 400RWHP plus. Also DPI have a new 8.8 unit that uses the c-clips so you don't have to change to 9" axle ends.

Colin

Colin, what is the DPI part number for the 8.8" unit that uses the OEM c-clip axles? Mike

 

[GR40Freak]

Colin, what is the DPI part number for the 8.8" unit that uses the OEM c-clip axles? Mike

I don't know, but I know it exists and its designed as a service replacemnet for the Trak-lok (no modifications needed). Call Randy at DPI.

Colin

 

[frank s]

.... in fact it's less stiff than many rears out there just for that reason, too much rear bar can play havoc with power down and diff life...

Long story short.... it's not too much rear bar. And he's got more front bar too.

I'd like to hear more about this. How does less roll in the rear shorten differential life? I have that 26mm rear bar (H&R) and the front is steeda's adjustable in the short hole. There is still some steady-state understeer, which I have reduced a bit with Koni Sport and tire pressure adjustments.

If what you mean by "power down" is that the rear wheels spin easily in second gear (3.73 gears), it's true, but it does that in any attitude, straight or leaning. GT500 18x9.5 wheels, Goodyear F1 Supercar 285-40s both ends (not the newer, softer ones).

I'd hate to think my poor showing in Sunday's autocross was because of that expensive metal back there, and not just my poor skills...

 

[SoundGuyDave]

Weight transfer in a corner is a function of lateral G imposed on the car. All the ARB does is adjust the attitude of the chassis above the wheels, but realize that the transfer is still happening. IF you run too soft a bar, or no bar at all (generic, not S197 specific), you get too much body roll, which translates to a large lateral shift in CG, and a LOT of mass in motion (momentum) to control, both on the set, and the recovery. Too much bar, however, can actually pick up the inside wheel, completely unloading it. As we know, a wheel in the air will NOT contribute to the tractive capacity of that axle! If the rear bar is too stiff, you wind up unloading the inside-rear tire, and that means wheelspin, and that means that different types of diffs will act differently. The Torsen, I believe, essentially goes "open" with one wheel unloaded. A spool (or locker) will not, but a spool will induce insane amounts of understeer under most cornering conditions. In a perfect world, you'll get your chassis dialed in to provide high enough spring rates to keep all four corners planted at max-Q in a corner, then add enough bar to keep the body roll to a minimum without disturbing the chassis set, and adjust the oversteer/understeer balance with the bar ratios front and rear.

Clear as mud, eh?

 

[GR40Freak]

Obviously different differentials will cause different vehicle behavior. One of the interesting things I've noticed about running a Torsen its ability to turn my FRONT end when exiting a corner.

For example: Exiting turn 6 (The Carousel) at Infineon Raceway, a fast,long, sweeping, down hill left turn. With the Trak-Lok, as I apply the throttle the Trak-Lok attempts to equal both wheel speeds, this causes the left rear (inside/unloaded) to spin slightly eliminating ANY traction that it had. So now all of the load is transferred to the right rear so if you try to accelerate, it will overwhelm the available traction of the right rear (i.e. the traction circle). This causes the rear end to slowly step out to the right, rotating the car counter-clockwise (over-steer) which requires right counter-steer. Its a fun way to drive a car but it requires a sharp skill set, especially sliding a car over 100MPH.

With the Torsen however, the cars behavior is quite different. With both differentials the left rear tire has most of the weight transferred away from it, therfore less traction, and it wants to spin. The Torsen transfers power to the wheel with the MOST traction, in the case of my example it would be the right rear. The left wheel rear puts as much power down as it can without causing the tire to spin, the remaining power is then transferred to the right rear. So even when applying throttle the tires are allowed to rotate at different speeds. Since the left tire isn't spinning, and is providing some, albeit minimal traction, the right tire can then put more power down than the Trak-Lok scenario. I can actually feel the right rear turning the car to the left without causing the car to over-steer. Obliviously the car will still over-steer out of a corner if you apply too much throttle, but the difference between the two-units in VERY noticeable as the Torsen allows you to apply more throttle out of a corner than you could with the Trak-Lok.

Also keep in mind that as a Trak-lok starts to wear it behaves like an open diff. This causes the vehicle to over-steer more, sometimes causing people to think that there is something else wrong with the car, not necessarily the differential wearing out. I can attest to it.

My stock Track-lok lasted less the 5000 miles and I've seen GT500 units wasted at 2000 miles. They just don't seem to last in anything other than regular street use.

Colin

 

[19COBRA93]

I had a Torsen T2R in my '93 Cobra. Absolutely loved it, especially on the street and at the autocross. It was ultra smooth and really was a gem. Unfortunately, 550 hp and a hard launch at the drag strip ended it's life. It literally crumbled. Sad, I really want another one, but I drag race too much to make it last.

 

[GR40Freak]

I had a Torsen T2R in my '93 Cobra. Absolutely loved it, especially on the street and at the autocross. It was ultra smooth and really was a gem. Unfortunately, 550 hp and a hard launch at the drag strip ended it's life. It literally crumbled. Sad, I really want another one, but I drag race too much to make it last.

True, its not a good unit for drag racing. For everything else though.. awesome.

 

[frank s]

Got roll-stiffness? Picture I took of a Honda at San Diego's Qualcomm Stadium, and one of my car at Chuckwalla Valley Raceway. In the first case, half the potential traction is wasted; in the second, too much transfer from the right side?



Thank you, Dave and Colin, for the enlightening. I get the picture, now, although it took some study and a few re-reads. It's not only the relative front-to-rear roll stiffness that's important, but the absolute stiffness, as well, and that is supplied in part by the anti-roll bars and springs.

The more I learn, the less I know.

Thanks again.

{On-track photos by CaliPhotography.com}

 

[frank s]

at least 3 characters

 

[Dreadknought]

sub'ed

 

[Rubrignitz]

Also DPI have a new 8.8 unit that uses the c-clips so you don't have to change to 9" axle ends.
Colin

Well that's exciting news. The first mod on my 2012 will likely be the DPI unit. The only thing holding me back from installing one in this car was the axle conversion.

Though I think I'm done sinking money into the 07. I'll yank the watts, dampers, bars, springs and transfer those to the new car. And the next one I'll drive off the lot supercharged via frpp.

 

[GR40Freak]

Just changing the diff on a stock car make such a noticeable difference.

Colin

 

[Sam Strano]

Have any more DPI information? I'd like to maybe carry them, but they are expensive and I'd like to know some things like bias ratios before even getting into the process of calling them to see about being a dealer, etc.

 

[Sam Strano]

Thanks Colin for the phone call.... I'll be sure to give they a ring on Monday to discuss in more detail. I appreciate the information and you taking the time.