Reason:

Increase the  envelope within which the car’s handling performance is predictable.

Considerations:

Cost was the primary concern as any Limited Slip Differential seemed to me to be an improvement over the stock B5 S4 Open Differential.

Options Available:

Stasis – Clutch type LSD.  By the time I got around to seriously considering the purchase of a limited slip differential the Stasis product was not an option I could acquire new since Stasis was no longer in business.

Guard Transmission – My understanding is this was the product Stasis used as the basis for their B5 S4 offering, it is a clutch type LSD.  ($2,250) Guard also offers a Torque Biasing Differential.

MFactory – Helical Limited Slip Differential ($999)

OS Giken – Clutch type. ($1,700)

Peloquin – Uses a planetary torsional differential but information specific to the B5 S4 is a little hard to find.

Quaife – ATB Helical LSD differential.  ($1,523)

Wavetrac – A design purported to address shortcomings in the Torque Biasing differential design, namely performance when a tire has little to no load applied to it. ($1,395)

Decision:

MFactory – I had signed up to receive notices and information from MFactory about their products and when I received an offer to obtain a unit as part of an overstock sale it was a deal too good to pass up.

Up until that point the two products I was most likely to buy were the Wavetrac and MFactory.  The Wavetrac marketing material makes it sound as though it is a little better on account of still performing when there is little to no weight on one of the wheels, one of the prime benefits of the clutch type LSD, but MFactory makes a good argument for their product, stating that for 90% of their purchasers the ‘lifted wheel’ scenario is not going to be encountered in all but extreme cases.  Considering how long I have been driving my S4 and never been aware of encountering a lifted wheel situation I figured it is a sufficiently rare occurrence to not matter in my decision making process.

The MFactory also claims a higher bias:

Regardless of performance differences, the MFactory product comes with a 30-day return option and a Lifetime warranty that transfers with the product.  Those were some manufacturing statements that convinced me that it was a good value option.

Satisfaction:

I am pleased with the MFactory LSD so far.  I’ve not driven my S4 hard enough to gauge how it handles now with the Limited Slip Differential versus the previous Open Differential, but there hasn’t been an adverse affects on the routine driving.  With the MFactory product frequently listed for sale at $799 it presents a substantial cost savings versus the other products I considered.

Long-term Report:

Too soon to tell.