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    Limited Slip Differential in the Turbo

    I understand that PAG offered an LSD for the 996 Turbo during its last year of production.

    Does anyone know the technical details of this LSD?

    Who has one? Any feedback on how it affects the handling of the car? The only comment I've found so far is this one:

    Re: LSD

    I have a 2001 Turbo and am considering retrofiting the LSD. Does anyone know if it is possible? Or how well it will work with the PSM?

    I recently added an LSD to my Audi S4 and am very impressed with what it has done to the handling characteristics of the car.

    Stephen


    Re: Limited Slip Differential in the Turbo

    Hi,

    it is possible to retrofit a LSD. But if you drive it hard you better switch PSM off. At least that's the way some friends are enjoying their cars. There might be an updated PSM available but I doubt it.

    Cheers
    Thomas

    Re: Limited Slip Differential in the Turbo

    Quote:
    Thomas said:
    it is possible to retrofit a LSD. But if you drive it hard you better switch PSM off. At least that's the way some friends are enjoying their cars. There might be an updated PSM available but I doubt it.



    Hi Thomas,

    Thanx for replying.

    This doesn't seem unreaasonable. That's the way most cars have to be driven. At the moment, I'm pretty much able to leave the PSM on all of the time. But I'd be happy enough if I could just leave it on during "normal" driving but had to turn it off on other occasions.

    I think one of the ways PAG has made the LSD possible on the 997 is to make it a very mild LSD. Do you have any info on how aggressive the LSD is that was installed in the Turbo?

    Last thought, why couldn't it be possible to upgrade the rear differential and also the PSM from the 2005 Turbo?

    Any feedback on how the Turbo is to drive with the LSD?

    Thank you.

    Stephen

    Re: Limited Slip Differential in the Turbo

    Interesting argument!
    noticed that on the specs of the 996TT presented by RC there was an LSD mentioned. I would have thought it only really makes sense on cars like the gt3 without 4wd, while cars with plenty of traction like the tt wouldnt need it.
    can anyone illuminate us here? an btw, does the 997tt offer that option as far as anyone knows?

    thanks!

    Re: Limited Slip Differential in the Turbo

    Quote:
    turbolite said:
    Interesting argument!
    noticed that on the specs of the 996TT presented by RC there was an LSD mentioned. I would have thought it only really makes sense on cars like the gt3 without 4wd, while cars with plenty of traction like the tt wouldnt need it.
    can anyone illuminate us here? an btw, does the 997tt offer that option as far as anyone knows?

    thanks!



    LSD will be available on the 997 Turbo as an option from the beginning.
    Regarding the advantages of LSD on a AWD car, this has been discussed in some older threads, searching the archives may be a good idea. If nothing comes up, we could start a new discussion about LSD on the Turbo. And yes, it was available for the 996 Turbo and Turbo S but I'm not sure if a simple retrofit is possible.

    Re: Limited Slip Differential in the Turbo

    thanks RC,

    just found this on the Manthey website:
    http://www.manthey-motors.de/mainframe.asp?lang=de&e1=199

    they offer an LSD for the tt at 65% and claim that on top of getting less slip at the rear inner wheel this would also help to reduce the stress on the viscodrive to the front axle.

    cheers

    Re: Limited Slip Differential in the Turbo

    Quote:
    RC said:
    Regarding the advantages of LSD on a AWD car, this has been discussed in some older threads, searching the archives may be a good idea. If nothing comes up, we could start a new discussion about LSD on the Turbo. And yes, it was available for the 996 Turbo and Turbo S but I'm not sure if a simple retrofit is possible.



    Hi Christian!

    The big problem I see on retrofit would be PSM and whether it had to be adapted to work with the LSD or not. I would guess not as I cannot see PAG investing the resources in adapting PSM for the last model year on a very low production option. But I might be wrong. If I am wrong, could PSM also be upgraded? Surely this is something that could be found out?

    As to the advantages of LSD on an AWD car, I did search before posting but didn't see anything. It might be that my search was not wide enough. Maybe this is a timely topic given the upcoming 997 Turbo?

    In any case, it would have tremendous advantages - especially on a rear engined car such as the Turbo.

    The central differential on the 996 Turbo is a viscous coupling. It splits power between the front and rear based upon the different rotational speeds of the wheels at the front and rear. It is reactionary. As the rear wheels begin to slip it moves more power to the front and vice versa.

    But this does nothing for the distribution of power side-to-side. At the front and rear these cars have classic open differentials. An open differential will not manage the power side to side. Traction is limited to whichever of the two wheels has minimum traction.

    On the Turbo the power tends to be predominantly at the rear. So what is actually happening is that as one rear wheel (often the inside wheel in a turn) starts to slip, more power is sent to the front by the viscous coupling. As the slippage at the rear increases so even more power is sent to the front. Ultimate traction is limited by the limit of traction at the front and since that is also an open differential, that too is limited by whichever of the two front wheels has the least traction (again, probably the inside wheel in a turn).

    So is it even fair to call this an AWD car? I think not. What it really is is a two wheel drive car. The difference is that the two wheels include one on the rear and one on the front (the one at the rear with the least traction and the one at the front with the least traction). How is this better than a RWD car which drives both rear wheels through a LSD? I'm not sure it is. It will be more stable because of the way that the power is split back-to-front but that's about it. The RWD car probably can put down more ultimate power - especially if it is a rear weight biased car such as the Turbo.

    So the solution is to add a LSD at the back of the Turbo. Now the power is first split between the two rear wheels. Before the viscous coupling comes in to play, there needs to be slippage on both rear wheels. Only then will the viscous coupling move power to the front of the car. It isn't practical to use an LSD on the front. So the car will ultimately become a 3-wheel drive car. It will also predominantly be a RWD car since the Turbo tends to send most of its power to the rear at first. So it would handle and feel much more like a RWD car - and this has always been the complaint against the Turbo - that it doesn't have that classic RWD feel of most Porsche 911 cars. As traction became limited at the back, some power would be shifted to the front so it would still have more traction than a RWD-only car and would also be more stable.

    So in my opinion, the LSD option on the Turbo is a most important option. And if I can, I would really like to retrofit an LSD to my own 996 Turbo.

    Stephen

    p.s. I would not object to moving this thread to the 997 Turbo board or possibly it is time to merge the two boards?

    Re: Limited Slip Differential in the Turbo

    Quote:
    FixedWing said:
    Quote:
    RC said:
    Regarding the advantages of LSD on a AWD car, this has been discussed in some older threads, searching the archives may be a good idea. If nothing comes up, we could start a new discussion about LSD on the Turbo. And yes, it was available for the 996 Turbo and Turbo S but I'm not sure if a simple retrofit is possible.



    Hi Christian!

    The big problem I see on retrofit would be PSM and whether it had to be adapted to work with the LSD or not. I would guess not as I cannot see PAG investing the resources in adapting PSM for the last model year on a very low production option. But I might be wrong. If I am wrong, could PSM also be upgraded? Surely this is something that could be found out?

    As to the advantages of LSD on an AWD car, I did search before posting but didn't see anything. It might be that my search was not wide enough. Maybe this is a timely topic given the upcoming 997 Turbo?

    In any case, it would have tremendous advantages - especially on a rear engined car such as the Turbo.

    The central differential on the 996 Turbo is a viscous coupling. It splits power between the front and rear based upon the different rotational speeds of the wheels at the front and rear. It is reactionary. As the rear wheels begin to slip it moves more power to the front and vice versa.

    But this does nothing for the distribution of power side-to-side. At the front and rear these cars have classic open differentials. An open differential will not manage the power side to side. Traction is limited to whichever of the two wheels has minimum traction.

    On the Turbo the power tends to be predominantly at the rear. So what is actually happening is that as one rear wheel (often the inside wheel in a turn) starts to slip, more power is sent to the front by the viscous coupling. As the slippage at the rear increases so even more power is sent to the front. Ultimate traction is limited by the limit of traction at the front and since that is also an open differential, that too is limited by whichever of the two front wheels has the least traction (again, probably the inside wheel in a turn).

    So is it even fair to call this an AWD car? I think not. What it really is is a two wheel drive car. The difference is that the two wheels include one on the rear and one on the front (the one at the rear with the least traction and the one at the front with the least traction). How is this better than a RWD car which drives both rear wheels through a LSD? I'm not sure it is. It will be more stable because of the way that the power is split back-to-front but that's about it. The RWD car probably can put down more ultimate power - especially if it is a rear weight biased car such as the Turbo.

    So the solution is to add a LSD at the back of the Turbo. Now the power is first split between the two rear wheels. Before the viscous coupling comes in to play, there needs to be slippage on both rear wheels. Only then will the viscous coupling move power to the front of the car. It isn't practical to use an LSD on the front. So the car will ultimately become a 3-wheel drive car. It will also predominantly be a RWD car since the Turbo tends to send most of its power to the rear at first. So it would handle and feel much more like a RWD car - and this has always been the complaint against the Turbo - that it doesn't have that classic RWD feel of most Porsche 911 cars. As traction became limited at the back, some power would be shifted to the front so it would still have more traction than a RWD-only car and would also be more stable.

    So in my opinion, the LSD option on the Turbo is a most important option. And if I can, I would really like to retrofit an LSD to my own 996 Turbo.

    Stephen

    p.s. I would not object to moving this thread to the 997 Turbo board or possibly it is time to merge the two boards?



    thanks for the exhaustive explanation!

    as you can see from the manthey website, it is possible to retrofuit the LSD. they do not seem to touch the PSM, but you might want to ask them, those guys know their stuff!

    Re: Limited Slip Differential in the Turbo

    Quote:
    turbolite said:
    thanks RC,

    just found this on the Manthey website:
    http://www.manthey-motors.de/mainframe.asp?lang=de&e1=199

    they offer an LSD for the tt at 65% and claim that on top of getting less slip at the rear inner wheel this would also help to reduce the stress on the viscodrive to the front axle.

    cheers



    65% would surely interfere with the PSM (which also includes the ABS), I would be careful. Manthey has racing experience but not that much 4WD experience.

    Re: Limited Slip Differential in the Turbo

    Quote:
    RC said:
    65% would surely interfere with the PSM (which also includes the ABS), I would be careful. Manthey has racing experience but not that much 4WD experience.



    Hi Christian,

    I totally agree. 65% would be quite aggressive. The unit I just installed in the Audi is 60/40 and even that makes a big difference. Isn't the one in the new 997S quite mild by comparison?

    There has been some technical discussion of this on another thread I started on Rennlist:

    Limited Slip Differential in the Turbo?

    Here is my thinking on PSM and ABS. This is all entirely speculative...

    I do not think ABS will be much affected by an LSD. The reason for this is that what LSD does is it make the two rear wheels tend to turn more together. It makes it harder (impossible?) to lock one under braking and not the other. This is a good thing. The ABS will continue to sense the speed of each wheel individually. To the extent that both wheels are working in unison, so will the ABS.

    So far as the portion of PSM that cuts the throttle is concerned, this will continue to work fine. Again, the throttle works on both rear wheels just as the ABS does. To the extent that the PSM senses a problem and cuts throttle then this will continue to work fine.

    The problem comes when the PSM system wants to differentially brake the rear wheels. When you start to spin or understeer, the PSM will operate on a single rear wheel to rotate the car around that wheel (or counter the current rotating force). But if braking the left-rear wheel also results in some braking force on the right-rear wheel via the LSD system, then PSM will have less ability to perform this differential braking function.

    I think my theory is born out by the 996 GT3 which came standard with a pretty aggressive LSD. The ABS system worked fine on that car. It didn't come with PSM.

    I suspect that a lot will depend on how aggressive the LSD is on the overrun (since we are talking about braking). If the LSD is too aggressive then it will interfere. If not, then maybe not. The $64 question is what that limit is. That's why I'd really like to know what Porsche put in their Turbos in the final year of production.

    I do think even if PSM is able to function with an LSD in the Turbo, it probably will still result in more intervention than before solely because it will change the handling characteristics of the Turbo so that it becomes a much more aggressive handling car which will tend to utilise PSM more often.

    Stephen

    Re: Limited Slip Differential in the Turbo

    Stephen - your logic is sound. Only the independent braking of each wheel is compromised with PSM. I'm certain that the PSM software was re-programmed to minimize issues with the 25% LSD that was available on the 40th Anniversary 996 (and on the 997S with LSD in Europe).

    If you have the ability to retrofit a torque-biasing diff (like Quaife), I think this would likely provide the least amount of intereference with PSM, as it only locks the axle on acceleration and would allow independence of the rear wheels under braking...

    Re: Limited Slip Differential in the Turbo

    Quote:
    Grant said:
    I'm certain that the PSM software was re-programmed to minimize issues with the 25% LSD that was available on the 40th Anniversary 996 (and on the 997S with LSD in Europe).



    How are you certain? I would think probably the main reason to use a 25% LSD would be so that they wouldn't need to re-engineer the PSM.

    Stephen

    Re: Limited Slip Differential in the Turbo

    My guess is that on a 25% LSD the PSM needs no adjustement but one thing I'm sure, a LSD is not a 100% all good device, its has its pro's and cons. You all know the pros (which are clearly blanted by the 4wd..) but what some of you don't know is that for instance a 50% LSD will make the car push (understeer) in tight corner so much you'll think the car has flat tyre! It will also make the car oversteer on throtle lift off (when PSM off) and makes the car more twitchy and unforgiving on the wet! Personally I'd only fit a LSD if I did a lot of other mods(like sport suspension,etc) AND if I'd disconect the FWD shaft which some rennlisters did...
    Otherwise my car (RoW suspension with -1,5* camber) DOES NOT need an LSD both on the dry and wet, on the road or on the track.

    One other thing for you power junkies...LSD's will make you "lose" a lot of horsepower when coming out of turns even if the inner wheel is not slipping, just for the friction generated during turns by different wheel speeds side-to-side.

    Re: Limited Slip Differential in the Turbo

    Quote:
    Kiko said:
    My guess is that on a 25% LSD the PSM needs no adjustement but one thing I'm sure, a LSD is not a 100% all good device, its has its pro's and cons. You all know the pros (which are clearly blanted by the 4wd..) but what some of you don't know is that for instance a 50% LSD will make the car push (understeer) in tight corner so much you'll think the car has flat tyre! It will also make the car oversteer on throtle lift off (when PSM off) and makes the car more twitchy and unforgiving on the wet! Personally I'd only fit a LSD if I did a lot of other mods(like sport suspension,etc) AND if I'd disconect the FWD shaft which some rennlisters did...
    Otherwise my car (RoW suspension with -1,5* camber) DOES NOT need an LSD both on the dry and wet, on the road or on the track.

    One other thing for you power junkies...LSD's will make you "lose" a lot of horsepower when coming out of turns even if the inner wheel is not slipping, just for the friction generated during turns by different wheel speeds side-to-side.



    Hmmm ... not sure about a 50% LSD making a car understeer (hard to turn in). Certainly a 80% LSD would do that. I'm running a 60% LSD in my Audi now and I don't have this problem at all. What is the LSD in the 996 GT3? That also doesn't seem to have this problem. In any case, I would think the solution on a street car is to limit the LSD to a point where it doesn't create this problem.

    No question about the car being more twitchy with the potential for more dramatic oversteer. This is a product of having both rear wheels connected. With an open differential, you will only overpower (or lift throttle brake) one rear wheel. With an LSD, you will do this to both wheel simultaneously.

    But wait a second. We are talking a Porsche here. It is a performance car. I guess it is a personal choice but my choice would be to have better performance even if it was at the risk of less stability.

    One big advantage that I think you've overlooked is that an LSD promises to change the handling characteristics of the Turbo from one that is mostly understeer to one that is much more controllable on the throttle and less understeer (maybe even oversteer?). Again, personal choice, but I personally don't like the understeer nature of the Turbo.

    I don't understand your "lose power" argument. How does slipping a wheel increase power? On an open differential, all you will do is spin one wheel. The LSD will drive the non-spinning wheel. How does that cost power?

    Stephen

    Re: Limited Slip Differential in the Turbo

    Quote:
    Kiko said:
    ...a LSD is not a 100% all good device, its has its pro's and cons. You all know the pros (which are clearly blanted by the 4wd..) but what some of you don't know is that for instance a 50% LSD will make the car push (understeer) in tight corner so much you'll think the car has flat tyre! It will also make the car oversteer on throtle lift off (when PSM off) and makes the car more twitchy and unforgiving on the wet!...


    My experience is that LSD greatly enhances off-throttle and braking stability. It does cause more understeer in very tight corners, but this can easily be corrected with swaybar adjustments.

    Also, the amount of power lost as heat through internal friction of the clutch plates is largely offset by the fact that the power reaches the pavement through both wheels, rather than being wasted as another form of heat energy (burning inside rear tire).

    Re: Limited Slip Differential in the Turbo

    Quote:
    FixedWing said:
    Quote:
    Grant said:
    I'm certain that the PSM software was re-programmed to minimize issues with the 25% LSD that was available on the 40th Anniversary 996 (and on the 997S with LSD in Europe).



    How are you certain? I would think probably the main reason to use a 25% LSD would be so that they wouldn't need to re-engineer the PSM.

    Stephen


    OK - "certain" was an overstatement, but I think they did change the software. 25% is still a fair amount of locking and I would think it enough to confound PSM to some degree without re-programming. Since the 997GT3 is due to have PSM, it will be interesting to see which solution they choose...

    Re: Limited Slip Differential in the Turbo

    Quote:
    Grant said:
    25% is still a fair amount of locking and I would think it enough to confound PSM to some degree without re-programming. Since the 997GT3 is due to have PSM, it will be interesting to see which solution they choose...



    According to JasonAndreas on Rennlist:

    Quote:
    The factory LSD for the G96.88 runs at 40/65%, part number #996-332-083-9B.



    So even more than 25% ... 40% on the overrun.

    Of course, the locking factor isn't the only issue but also the pre-load.

    This gets more and more interesting.

    Stephen

    Re: Limited Slip Differential in the Turbo

    Quote:
    FixedWing said:
    Quote:
    Grant said:
    25% is still a fair amount of locking and I would think it enough to confound PSM to some degree without re-programming. Since the 997GT3 is due to have PSM, it will be interesting to see which solution they choose...



    According to JasonAndreas on Rennlist:

    Quote:
    The factory LSD for the G96.88 runs at 40/65%, part number #996-332-083-9B.



    So even more than 25% ... 40% on the overrun.

    Of course, the locking factor isn't the only issue but also the pre-load.

    This gets more and more interesting.

    Stephen


    Stephen - Usually the overrun percentage is the higher (and stated last), so it seems to me that it's 65% in the overrun. It's desirable to have more locking under braking than acceleration to reduce understeer in slow corners and maximize braking stability and corner entry. Is this part you referenced the one that comes in the Anniversay 996 or the Turbo?

    Yes, you're correct about the preload being very relevant. Porsche is not consistent with their "percentages". Sometimes a much larger torque is required to "unlock" the axle even if the two diffs have the same percentages.

    Re: Limited Slip Differential in the Turbo

    Grant, Stephen,
    Been reading this thread with great interest as I do have LSD on my 911 and understand the physics behind it but not too sure how the device actually works.
    An LSD is usually described with two locking numbers x/y expressed as percentages.
    I thought x was the blocking factor under acceleration and y under braking. Am I correct?
    And also, if my understanding of an LSD is right, then whatever the rate of blocking of the latter, PSM must be reprogrammed as they basically do the same thing: Provide ultimate traction.
    One being a sporty device, hence distributing power between the two driving wheels.
    The other being a safety device, hence braking the wheels with most traction.
    One optimises traction, the other compromises it.
    Does it make sense?
    I would have thought that Porsche engineers reprogram the PSM so that it intervenes only once the LSD reaches its locking rate under acceleration in tight corners for example.
    BTW, thanks for this thread! It had been an eternity without a proper sports car discussion!

    Re: Limited Slip Differential in the Turbo

    Quote:
    Grant said:
    Usually the overrun percentage is the higher (and stated last), so it seems to me that it's 65% in the overrun. It's desirable to have more locking under braking than acceleration to reduce understeer in slow corners and maximize braking stability and corner entry. Is this part you referenced the one that comes in the Anniversay 996 or the Turbo?



    This time I think you are wrong Grant. Usually the drive locking factor is higher than the overrun locking factor.

    Why you would want a high locking factor on drive is obvious. The reason you usually want a lower locking factor on the overrun is that a high factor will tend to interfere with your ability to get the car to turn in in slower corners (both rear wheels turning at the same speed will try to keep the car going straight) and in higher corners will tend to give more oversteer as both rear wheels will be effected by lift-throttle braking (rather than just one before).

    On the track this is less of a problem. Presumably the driver is more competent and less likely to get caught out. Also, because of the speeds he is driving, the tyres tend to be slipping more and that makes it easier for the tyres to deal with the forces exerted on them by the LSD.

    The LSD I just installed in my Audi is 60/40. It is 60% under power. That makes the car feel like a classic RWD car under power. It is 40% on the overrun. That makes the car quite benign during braking and corner entry. I actually wish it had a little more effectiveness on the overrun as I like to get the car to rotate a little on the entry to slow corners and that would help me do that.

    Stephen

    Re: Limited Slip Differential in the Turbo

    Yes,

    Good discussion. FixedWing, I would modify your statement that the 996TT/TTS drivetrain makes the vehicle really a "two wheel drive car" to say that it's a "two axle drive car." I also believe the PSM would need reporgramming with any LSD system installed, no matter the locking/overrun percentages, although, true, the less the locking percentage, the less the interference.

    Re: Limited Slip Differential in the Turbo

    Hi Fanch,

    Always happy to shake things up a little around here.

    On LSD and PSM working together ... not quite. In fact, when it comes to the important bits of PSM (its ability to brake wheels individually to put rotational forces in to the car), PSM and LSD actually fight each other.

    The goal of an LSD is to better distribute torque to where it is needed. As the speed difference between the rear wheels increases, the LSD will redistribute the torque to the other wheel. In this way, it is able to get more torque to the road.

    Think about what PSM is doing. As you start to spin out, PSM will apply the brakes on an individual wheel to counter the rotation of the spin. Those who have experienced this know that it does this quite aggressively on the Porsche.

    Now consider the interaction of PSM and LSD. As PSM brakes the left-rear wheel, that wheel slows. The LSD now sees a difference in wheel speeds between the left and right wheels. The LSD will now redistribute that new torque from the left wheel to the right wheel. That will slow the right wheel. This counters what the PSM was trying to do which was to get just the left wheel to slow so that it could put a rotational force in to the car.

    LSD's transfer a maximum percentage of torque side-to-side. So in all likelihood, an LSD set to transfer 80% of the torque would seriously interfere with the functioning of the PSM. Speculatively, I would guess that one designed to transfer a maximum of 25% (still a very useful figure) would not. Now the $64 question, how high a percentage could one use before it will interfere with PSM?

    Everyone speculates that PorscheAG must have modified their PSM to handle the LSD. My gut says no. Re-engineering a PSM system takes a lot of effort and big bucks. Why would they do this for an optional item on the final year of production? I think it is far more likely that they simply tried different LSD's until they found one that was effective yet had a low enough lock-up factor to still allow the PSM to work normally. After all, if the LSD is interfering with the ability of the PSM to function at the wheels, how will reprogramming fix that?

    Stephen

    Re: Limited Slip Differential in the Turbo

    Quote:
    FixedWing said:
    Quote:
    Grant said:
    Usually the overrun percentage is the higher (and stated last), so it seems to me that it's 65% in the overrun. It's desirable to have more locking under braking than acceleration to reduce understeer in slow corners and maximize braking stability and corner entry. Is this part you referenced the one that comes in the Anniversay 996 or the Turbo?



    This time I think you are wrong Grant. Usually the drive locking factor is higher than the overrun locking factor.


    Stephen - I think pehaps the confusion comes from comparing a 911 to an Audi. The 911 has inherently so much more traction under power, so it requires less locking on accleration than an Audi with its engine in front of the front axle line. An Audi Quattro has a natural tendency to understeer when braking into a corner, so requires less lockup there...

    I recently specced a custom Guard LSD for my 73RS, so I became very involved in the process and theory. I am certain that cars like the GT3 have asymetrical LSD with MORE lockup on overrun (braking) than power (my 911 does too). Porsche first developed the asymnetrical LSD for the 911 Turbo where I believe it had only 20% under power and 80% or more on braking to remove its nervous tendency of wanting to spin under trail braking into the entrance of corners. It didn't need more than a modest amount of locking on the power, since over 60% of the weight is already over the drive wheels (and even more dynamically as the weight transfers rearward under power).

    There is some interesting info from the PCA about the 996 Anniversary model's LSD here (where it describes 22% locking on power and 27% on braking):

    http://www.pca.org/tech/tech_qa_question.asp?id=%7B5935B803-3FEE-446D-B63C-87240E0FB690%7D

    Also, please read this under G-50 5-speed and 6-speed:

    http://www.rennsportsystems.com/1-d.html

    where it says among other points of interest:

    "The strongest variant of this gearbox is the G-50/50, used in the 89-on 3.3 Turbo and C2 Turbo. The G-50/52 used in the C2 Turbo also featured an asymmetric Limited Slip Differential that had a 20% lockup on acceleration and 80% in braking to help limit trailing-throttle oversteer."

    Also, if you locate the Porsche press release for the GT3 (2004), it describes the asymetrical LSD in detail and provides its higher lockup ratio under braking. I initially assumed this was a typo, until I later learned the reason...


    Re: Limited Slip Differential in the Turbo

    Thank you Grant for really opening my eyes. At first I thought you must be wrong. But now I believe you.

    What it really goes to show is how different these set-ups can be in different cars and how one solution does not fit all.

    I'm still wondering what PAG actually put in the last year 996 Turbo. And I'm also wondering what will actually live successfully in a Turbo. and lastly, I'm wondering what would be ideal in a Turbo. Not easy questions to answer by just chatting on a forum.

    Anyway, I do think this will have a dramatic affect on the Turbo.

    Curious your reaction to your own LSD?

    Stephen

    Re: Limited Slip Differential in the Turbo

    Quote:
    FixedWing said:
    Curious your reaction to your own LSD?



    Stephen - It's my pleasure to chat about this topic. I have been VERY impressed with the Guard asymetrical LSD in my 73RS. The car used to squirm quite a bit under hard braking, but now it is far more stable. I used to have to limit myself to braking only in a straight line before reaching the corner or I'd be in for quite alot of oversteer. Now, I can brake pretty deeply into the corner with less likelihood of oversteer or locking a rear wheel (no ABS).

    Of course, there is far better traction on the exit of slow corners too (more commonly known benefit of LSD) and I can get on the power quite early too. In general, the car is just more composed in every way.

    I did tweek the swaybars (infinitely adjustable Charlie Bars) to prevent understeer which is more prevalent in slow corner with a clutch-type LSD, and now the balance is wonderful. It can be totally steered with the throttle and modulated from understeer to neutral to oversteer all with the right pedal. It's tons of fun. And the build quality of the Guard stuff is bulletproof.

    I agree that there is certainly not a "one size fit all" approach that works with LSD's. Since your car is AWD, turbocharged, and has PSM, you'll need to consider all these factors (which you clearly are). I wish I knew more about what Porsche did to implement the LSD in the 996TT (setting the locking ramps for overrun and power, PSM mods, etc.), but I don't have any concrete info.

    I do feel that any serious track work benefits tremendously from a proper LSD, both in laptimes and driver confidence. I find it a real shame that none of the new Porsches (other than the GT cars) comes with one in the US now

    Good luck and keep us updated with what you uncover

     
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