Malakas

A friend of mine just bought a 987S, and we were "b.s. racing" today, trying to figure out who would be quicker around a track.

It then dawned on me that neither my 2002 996 C4S, nor his 2009 Boxster S had a limited slip diff. I find this strange considering how the "M" cars pride themselves on their "M-diff", and even my 2005 Honda S2000 had a LSD. In fact, I can't think of a modern or semi-modern sports car without one...

I assume that Porsche just didn't think their cars needed one?? I know it was a costly option... but why wasn't / isn't standard...

Anyone know the thought process here?

jasper

My understanding is that PSM is meant to replace the LSD. I guess it's true since the PSM brakes whatever wheel is slipping, at which point the open diff sends the power to the side that isn't.

The benefit of PSM overthe LSD is that the PSM doesn't fight the wheels during normal operation around a tight bend, when one wheel is legitimately turning at a different speed than the other. I haven't got that much experience with posi rear ends, but I do know that really aggressive ones don't like to make tight turns.

The Cayman would smoke your a$$ at the track by the way.

Edgy01

Porsche has begun to reintroduce (i.e., make available) LSD for the 997 cars. Initially you couldn't get it for USA models. The PSM is supposed to handle many of the things that we used to have LSD for on earlier 911s.

Rob in WA

It adds complexity - and is mainly beneficial on the track - % of owners who track their cars is pretty small.

Meister Fahrer

The rear engine puts more weight over the the drive wheels, which also lessens the need for LSD.
The other reason seems to be a combo of technology (PSM, etc) and cost savings.

But LSD also has benefit under deceleration, i.e. lift throttle oversteer is a bit more controlled as both rear wheels are acting together.
There was a good article on aftermarket LSD for 996 and 997 in a recent Excellence.

In my car, I do feel I can generate a small controllable slide and still have good control, like the LSD helps do both.....

adg44

Exactly.

Holger B

It's standard...on the GT3.

Moderato

It seems like everything is always a trade-off of some kind. I believe the Torsen type LSD was designed to eliminate the "fight" but the way it works, if one wheel has zero traction then it acts as an open diff. I'm not sure of the specifics but that's my understanding of it. Other then that the choices for LSD's are mechanical, viscous or electro-magnetic clutch.

Before computers made it possible to independently and effectively control brake calipers, a mechanical LSD was an absolute necessity. I suppose the freedom with which an open diff operates in turns, coupled with a computer controlled brake-LSD simulator, is perhaps a viable option for a daily-driver. The more rigorous demands of track driving would require a more aggressive setup to favorably handle the differential.

I believe the best AWD system you can have now is the electro-magnetic clutch type which can vary lock up on a more complicated set of parameters then was previously possible. This type of setup is difficult to get perfect and in the past has been expensive & complicated. Lately, more of these systems are starting to become good options for mass produced cars.

At least this is my understanding of the whole complicated situation and I'm typing this as I'm watching the latest X-files movie which isn't what I was expecting before I started it. What was I talking about again?

CarlosR

Hey, my C2 996 cab has it. You just had to check the right option box when you ordered.

P.S. You also had to order in the right year!

pszikla

if you don't have LSD on an older Porsche ("99C2) without PSM does that mean that you only have 1 powered wheel all the time, or that either wheel puts the power down but not both?
Pete

redridge

with the way Porsche finances are... the people at Porsche are on LSD.

Holger B

My 99 C2 had it also (which I ordered), but I don't think it's the same as on the GT3. Not even sure it was a real LSD.

The other thing to consider is that the GT3 LSD has clutch packs that wear. One more maintenance item to have to deal with eventually.

Thundertub

I have a '99 C2 that does NOT have LSD. I track it frequently and have never needed an LSD because even with 300HP the inside rear wheels do not spin in even the sharpest accelerating corners.
However, on the street, accelerating with power from a stop around a dusty corner quickly spins the inside tire. I am certain that would also be a factor if I lived where the snow falls (but I don't). I have had LSD equipped Porsches in the past. I would order it again if I were to buy a new Porsche. I just don't know that it offers that much help on dry roads. But in slippery conditions, or with a LOT more horsepower (i.e.GT3's and lots of expected track use), I can easily see why you would want it.

LJpete

It's helpful in Autocross. Especially, in really tight corners. I've been able to break the inside tire of a friends 02 where my 99 with lsd didn't have that issue.

Patrick E

My car doesn't have LSD, but I've noticed when I hit apex curbing on the right side that my car has trouble putting down power if the apex is particularly bumpy. Never had that problem on my old car (with lsd).