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Originally Posted by CJ_Boxster
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Limited slip differentials are not all created equally and not all of them are appropriate for all applications. What I mean by this is there are downsides to each of them, and what the car's primary use is should dictate what kind of (if any) LSD should be used.
For instance one of the upsides to a mid-engined car is its willingness to change direction quickly. One downside to a mid-engine is that when power is applied exiting a corner, the rear weight bias can increase understeer.
Blindly installing a clutch-type LSD would cause a mid-engined car to have increased corner ENTRY understeer because it limits the maximum speed differential between the two rear wheels. Some people feel this detracts from the car's steering feel as well. On corner exit it will exacerbate the car's desire to go in a straight line, causing even more push unless tuned out with suspension adjustments or driving adjustments. So it's not all hearts and bunnies. In fact these reasons are why Lotus initially did not offer an LSD on the Elise - they claimed it would actually make the car slower around a racetrack and be less "precise" feeling.
On the other hand a torque-biasing differential like a Quaife effectively acts like an open differential on corner exit, but a clutch-type on exit. This would be a good choice for a car like the Boxster, but it's still not for everyone. The main downside to a quaife is if one wheel is on a high-grip surface and one is not, the differential will act like an open diff. So on snow or ice, it's not ideal.
All that said, I would certainly have ticked the box for a Quaife had it been offered on the 986. But it's not a huge deal that the car doesn't have one, and nobody who doesn't compete with (or do track events with) their car should care because for the street driver, it's perfect the way it is.
