confusion on limited slip differentials

[John Edward Miller <jem@xxxxxxxxxxxxx>]

>    I've been reading about the lsd and i'm kinda confused. Is there two
> different products using the same name? I read about one lsd that deals
> with  the gears and improving acceleration and one lsd that deals with
> the wheels  and improving the wheel traction.
<snip>
>  I'm looking for a product that would give my car faster acceleration and
>  i  think this might be it. But i'm not exactly sure what is what. If you
> guys  can help me out that would be great.

First, on the diffs:  One is a traditional friction-type limited-slip that 
attempts to deal with wheelspin by controlling the difference in speed 
between the wheels on opposite sides of the car.  This is done with 
clutches inside the differential body.

The other is a Quaife worm-gear-type torque-biasing differential.  The 
premise here is that a series of worm-gears are arranged inside the 
differential in a way that (highly oversimplified) causes a wheel that 
loses grip to actually tighten the worm gears against the diff case, 
causing the side that has grip to get more torque.

Some racers have a preference for one over the other.  Car setup and 
cornering balance can be a factor: in conditions of marginal grip, the 
clutch-types put more force through the inside drive wheel in a turn, the 
Quaifes (and Torsens, and TrueTracs, and Gold Tracs, and other similar 
designs) put more force through the outside drive wheel.  Clutch-type 
limited-slips wear, a Quaife will normally retain its effectiveness 
indefinitely, but they generate heat when used hard and long track sessions 
(30-40+ minutes) with high-HP engines will push diff-oil temps way up and 
may require a cooler.

Second, on the goals: If your goal is faster straight-line acceleration in 
street use, and you're not currently traction-limited (that is, you're not 
spinning wheels) you're going to see no gain from either of these products. 
If you are traction-limited, either one will help and there's not much to 
choose between them in general street use.

I am, to this point, on the worm-gear camp; I have a Gold Trac in my track 
Mustang, a Quaife in my Taurus SHO (another advantage of the worm-gear 
torque-biasing diffs is that they can be used in FWD vehicles; clutch-type 
diffs set up loose enough to be usable in FWD are generally not very 
effective) which also sees a certain amount of track time, and am waiting 
for the E39 5er Quaife to be available - rather frustrating that the E39 
540i goes out the door with an open diff, DSC is not an acceptable 
substitute.

John.

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