What does Porsche have against the LSD?

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?

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.

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.

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

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.....

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Exactly.

It's standard...on the GT3.

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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?

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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!

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

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

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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.

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.

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.

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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).

I feel the LSD makes a huge difference on street and track, especially once you stiffen the suspension one can get inside wheel spin and if the car has already taken a set on exit - the rear is loaded and you stop accelerating this makes matters much worse. I have several threads about this very topic and really don't understand why some sort of locking differential was not standard. I was getting inside wheel spin each lap on oak tree VIR; would never consider doing an autox in this 911... The diff on my M3 was nothing to write home about but at least it was standard. The GT3 LSD seems more aggressive than the E46 m3 diff, I can feel it engaging more on track. I have yet to ride in a car equipped with the Guards unit... Looking in DE forum you will see posts of people claiming 2 second lap time improvements from just the LSD. You gain significant rear grip under turn-in and are not having to drive around wheel spin on exit. I was mainly interested in LSD because the car is much more controllable when the rear steps out.

Thanks for all the replies. I mean dont get me wrong... the (few) times I've tracked the car, it was marvelous. It just seems a little cheap of Porsche to use electronics when a good mechanical LSD would be preferable in the environment the car was designed for.

Factory LSD is a pretty rare option for any 911 but it makes a huge difference. Drive one back to back with and without and you will want it.

Hopefully it was worth the 4 1/2 year wait for Malakas to get his answer.

One must have patience Grasshopper.

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An LSD, Limited Slip Differential, is pretty useless unless you have one tire with more, enough, traction vs the opposite tire. On the other hand a Torque Sensing, Torsen, differential would be highly desireable on the track. For most of us the TC virtualization, simulation of an LSD will be more than satisfactory.

40th AE's all have LSD

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Braggin' or complain'n?

Note the original Porsche diffs wear out if you track a lot, a Guard rebuild is a great way to replace it. Very happy with mine and it gave me 4 secs a lap quicker at the Glen..

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Braggin'

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Yup. LSD, you want it. Keeps the TC light off and the power on. It works on the street. Streets have sand patches, puddles, bumps and sometimes even snow.

I just put a limited slip diff in my 2004 c2 (PSM) I bought a used lsd out of a crashed 2004 40th anniversary edition . The porsche lsd , is a bit weak with its brass disks and weak ramps , it is known for wearing out quickly on the track and at about 40-50k miles in a street car . But guard transmission makes a kit that essentialy takes the same internals they have in their own aftermarket diff and upgrades the porsche one , not only is it more robust and longer lasting , it performs better . I had the GT rebuild done and installed in my tranny . At the same time I installed a set of h&r street performance coilovers , h&r swaybars and upgraded every bush with powerflex purple street poly bushes . What a great combination , it reminds me of a gt3 but without the bone jarring ride . The lsd combined with the suspension really transforms the car . Monster grip coming out of the corners , the power is just so tractable , and easy to get down . If your car is mostly a commuter and hi way car , it's probably not something you need but if you track , auto cross , de or just love attacking the twistys , it's an amazing upgrade . Quaiff and wave track make geared ts diff which are much cheaper and good offt he line but a plaited diff like a porsche or a guard one gives you deceleration lock up too , but cost a lot more . Unless you luck out like I did and find a used one to rebuild . I love it , a whole new world traction wise . And it works just fine with the PSM , even with a 40 60 split . The PSM just doesn't kick in as much . IMO , the lsd is a better investment than aftermarket exhausts and intakes , if it's performance you're after . Power to the wheels!

I have one on my Jeep, 180k miles later and I have doubts if it's working anymore. They seem to wear out and need rebuilding, and imo, psm would do a better job with brakes anyway than the clutch in a lsd could. That said with the normal engines there is so much weight back there and the tires are so wide that for normal use I'm not sure how much of a benifit lsd would give, and again it'd need to be rebuilt maybe as often as a clutch is replaced. Gt3 or more horsepower and it's a different story.

I've had my PSM car for over a year . Putting the plate lsd in has made the car perform dramatically better in and out of the curves . Off the line acceleration is night and day better . When you stomp on it off the line in the PSM car , when the driven wheel spins , the brakes kick in and bog the car down until traction is regained . With the lsd , power is transferred to both wheels , the car grips and shoots off the line , if one wheel breaks traction the other wheel takes the drive , if the PSM kicks in its only for a fraction of a second , you don't get the bogging down sensation . You really need to drive both to understand it .

Interesting write up on diffs from pelican http://www.pelicanparts.com/techarti..._and_Seals.htm Plate diff video Understanding Limited Slip Differential - YouTube Torsion diff Torsen Differential, How it works ? - YouTube

Good faq from the gt3 guys https://rennlist.com/forums/996-gt2-...ntial-lsd.html https://rennlist.com/forums/gt2-and-...d-install.html Guard rebuild

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That is a huge drop in time.

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Is that limited slip?

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Maybe, maybe not. Check for 220 on the hood options list. The other check is to jack up the back end of the car and spin a rear wheel by hand. if the opposite side spins in the same direction, you have an LSD. The LSD is beneficial when the wheels have different levels of traction (one on pavement, one on ice). With an identical surface, both tires will spin.

Stability management plus the ABS pump can do a fine job of keeping the car pointed in roughly the right direction. Since stability management is one of the many safety features mandated by the US, Porsche _has_ to include it. When you consider that the VAST majority of drivers won't appreciate the fact that the PSM/ABS solution results in less power getting to the road, Porsche has little incentive to install a "real" LSD in a car that is already equipped with a system that can simulate the effects of an LSD anyway. The bummer, of course, is that more and more of these stability systems are designed to be non-defeatable. Even if it has an off switch, odds are that you can't turn it off, at least not completely. The LSD is just one more reason why I like my '96 Corvette. When I press the ASR button, the slip reduction system is REALLY off - and there's an LSD in that differential that actually works the way I want it to, and it isn't some pansy LSD that is going to need a rebuild after a couple of track sessions.

I keep my LSD in the frunk, usually windowpane, fluff, or sunshine. I can't stand that pansy cocktail LSD, like that crappy paper chit with a carebear or unicorn thingy on it.

Since putting the guard equipped lsd in my car , it's not just traction off the line . It's how much harder you can go into corners and have such control . The deceleration lockup is just as important as the acceleration traction .

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I used to get mine from Owsley back in the day

I miss the good stuff

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Yeah, a Porsche mechanic was telling me even though you turn it off, if the car senses you are heading for the trees or some other extreme condition it turns itself back on.

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Well, my thought and my friends thought of LSD is it will grab if a tire is slipping. It's not really something that happens right off the line in it's true form or at least our understanding of it - unless it's setup for a race or something. I think I have it, and I spun out a little with one tire on gravel and the other on pavement. The one tire started to spin, then the other one grabbed and pulled me out and forward. Not sure how that got in there as I don't have code 220, although it did seem to be a pretty sorted car when I got it (aside form the rattling muffler) so I'm thinking someone updated that at some point. [edit] I don't have PSM, so I'm wondering if they didn't put in LSD in leiu of that option. Which also would somewhat explain why it's not on the build sheet as it wasn't, at that point, an option.

With these cars the LSD really helps on heavy deceleration, at high speeds on the track. When I added the LSD to my old track car the tail wagging under heavy decel stopped immediately.

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No there is no ESP option, but if you turn off PSM, stepping on the brake pedal reactivates PSM.

Yeah - doesn't Psm not only apply brake - but cut throttle ?

PSM only comes back on ( if you manual disengaged it) if you brake hard enough to activate the abs , smooth non panic braking won't turn it back on. Late PSM 5.7 will cut throttle if it detects the car is in a full on spin . Earlier 5.3 PSM won't . My car is a later one , it does better doughnuts if the PSM is turned off first .

It is a falsehood that PSM reactivates when you hit the brakes. PSM will reactivate if it determins you are an assclown, though. I have had a single instance where mine came back on - after a series of pathetic fails to catch a spin that resulted in even more tire-smoking spin, but otherwise it has stayed off when asked to do so. PSM can retard timing and/or cuts throttle in addition to modulating the braking. The system is fairly smooth - I've only felt it a few times under acceleration when one tire loses traction. Compared to the ASR (active slip reduction) equivalent in my Corvette - which is about as subtle as a snapped drive shaft and makes a loud and very unpleasant noise under the hood when it's working - the 996's PSM is subtle and light-handed. Note that I cannot comment on how PASM works - my 996 is too old for that fancy 33% longer acronym.

In porsche 996 the essential companion , it states the PSM comes back on if abs is activated in hard braking. More here http://www.total911.com/technology-e...ty-management/ It's not that hard to try it yourself and see Good article on PSM http://www.deter.com/porsche/PSM.html

LSD and PSM, PASM are really not required on a 996. Get a proper suspension setup and you will have no trouble keeping up with a newer GT3. I say that from experience. I think these were big selling points for new drivers who want to floor it with the wheel turned during hard rain.

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You must be a very awesome driver.

Or on a track with newbies .