Limited Slip Diff

[Plan B Racing]

In the 2008 rules, there is a Ford OEM listed for the Getrag 6 speed for the SVT. Is this wrong? I was under the impression that SVT's had an open diff. When I looked up the part number it is a Torsen.

Also, the rules don't mention welding an open diff. Is it legal to weld in Spec Focus?

[Jefe]

I wouldn't think you'd want to weld the diff in a FWD car.

[Ted7rns]

Since it looks like the wording for the Rally SF is the same as the Road Racing SF, Then I would say no you can't weld it. No place does it say you can weld it... so it would fall under rule #4.0

4.0 Format
Modifications, addition or removal of parts are not authorized, unless specified or approved in these rules. Additional modifications are not permitted. These rules are not intended as guidelines; rather they shall serve as the national set of rules, and must be strictly followed. NASA Rally Sport is responsible for ensuring that all competitors running in the corresponding regional series conform to these rules.

But, I don't want to step on anyones toes, so Ask John Shirley.

[apotropaic]

You would ONLY want to weld your diff in a FWD car if it is drag ONLY.

[BigSandwich]

Ted is correct since it does not mention it you can't do it.

To my knowledge the dif in the SVT is open. I know that Hampton put the quaife in his car.

Welded difs are popular in FWD rally cars as a cheap alternative to expensive clutch pack LSDs. One of the arguements for them is that if destroy a corner of the car you can still drive the thing where with a Torsen style dif you are stuck.

The draw backs to welded dif like increased understeer and wear on axles are significantly lessened when you are dealing with a loose surface event like Rally. Also, I know of 2 manufacture backed FWD cars here in the states that tried several dif options but ultimately settled on a welded diff as the best option.

[BUR_ZX3]

Right.

I don't know that you'd want to run welded dif on a tarmac rally.... but on gravel or snow.... you're good to go!

[Z63R]

Another voice here for not welding a fwd differential for tarmac use... and the Torsen or even a Quaife is not a traditional, clutchpack style limited slip.

The Torsen is referred to as an automatic torque biasing differential, and as such will send torque to the wheel that has the most grip. This should mean that contrary to what our dear friend BigSandwich just posted if a front corner of the car is destroyed, one should be able to get drive torque to the other side of the front axle and therefore retain perhaps some necessary motorvation to limp onward.

:-)~

[Plan B Racing]

The car is for Built for Off Road Rally not Tarmac events. With so few Rally Tarmac events 2 maybe 3 nation wide, I don't really see it being an issue. Guess I will have to buy another trans for Tarmac events. Great another expense.lol

[BUR_ZX3]

Its an issue only if you want to turn on tarmac.

Trust me.... diffs are open for a reason. Otherwise they'd be solid from the factory.

[brads03zx3]

Originally Posted by Z63R

This should mean that contrary to what our dear friend BigSandwich just posted if a front corner of the car is destroyed, one should be able to get drive torque to the other side of the front axle and therefore retain perhaps some necessary motorvation to limp onward.

This is only true if both wheels have at least some traction. 0 times anything is still 0. If the entire wheel or hub fell off up front, the car would be immobile with a torsen or a quaife, unless the damage happened to seize up the axle on that corner.

[BigSandwich]

Originally Posted by Z63R

Another voice here for not welding a fwd differential for tarmac use... and the Torsen or even a Quaife is not a traditional, clutchpack style limited slip.

The Torsen is referred to as an automatic torque biasing differential, and as such will send torque to the wheel that has the most grip. This should mean that contrary to what our dear friend BigSandwich just posted if a front corner of the car is destroyed, one should be able to get drive torque to the other side of the front axle and therefore retain perhaps some necessary motorvation to limp onward.

:-)~

Sorry man. Torque biasing requires some torque to bias. It is a known fact that if a quaife or torsen dif has one wheel in the air no wheel on the car it will not generate forward movement for the car. It does not need much but it needs something.

Also, no one is arguing that a quaife / torsen is a clutch pack dif because its not.

[BigSandwich]

Originally Posted by Plan B Racing

The car is for Built for Off Road Rally not Tarmac events. With so few Rally Tarmac events 2 maybe 3 nation wide, I don't really see it being an issue. Guess I will have to buy another trans for Tarmac events. Great another expense.lol

You can run a welded diff for tarmac. All the rally cars that have welded difs still have to transit on tarmac roads. The car will handle strange but it will be predictable. Talking with people that run welded difs on rally cars you just need to be extra careful during real slow speed stuff or when turning the wheel to full lock like parking.

[Z63R]

Sorry man.

No argument here. Hence the words, "should" and "perhaps" in my post.

My understanding of atb diffs was incomplete... and I am now better informed thanks to you, sir.

:-)~