limited slip differential lock-up?
10-23-2007, 10:06 AM
#1
Rennlist Member
Thread Starter
limited slip differential lock-up?
Does anyone know what the lock-up on acceleration/deceleration is on a limited slip differential for the:
stock 968 LSD?
Porsche Motorsports LSD?
993 or 996 LSD?
Cup car LSD?
txs
Dave
stock 968 LSD?
Porsche Motorsports LSD?
993 or 996 LSD?
Cup car LSD?
txs
Dave
10-23-2007, 10:37 AM
#2
Nordschleife Master
The Porsche Motorsport LSD is typically 40/65%. There are different versions, early ones have 4 plates, later ones have 8 plates
Cup Cars run the Porsche Motorsport LSD so it is 40/65.
993 Street has 25/65, 22/40 (2 plate version that wears prematurely when abused)
993 RS has 40/65 (motorsport)
964 street has 40/40
964 Turbo has 20/100
964 Cup has 20/100
Paul Gaurd has 50/80 and 80/80 with other options available
968 have a torsion diff at 40% lockup
Cup Cars run the Porsche Motorsport LSD so it is 40/65.
993 Street has 25/65, 22/40 (2 plate version that wears prematurely when abused)
993 RS has 40/65 (motorsport)
964 street has 40/40
964 Turbo has 20/100
964 Cup has 20/100
Paul Gaurd has 50/80 and 80/80 with other options available
968 have a torsion diff at 40% lockup
Last edited by Geoffrey; 10-23-2007 at 11:13 AM.
10-23-2007, 11:21 AM
#3
Rennlist Member
There are two types of 968 locking differentials that were installed by the factory. A ZF clutch type LSD, and a Torsen type (torque biasing) differential.
I believe the ZF is a 40/40, but not certain.
The torque biasing type really are not rated by a lockup %. Because of the internal gear mesh design versus friction discs (of the clutch type LSD), there is zero slip, but it does not function like a 100% locked spool - since the wheels can still spin at different speeds. And they are basically open when unloaded.
I believe the ZF is a 40/40, but not certain.
The torque biasing type really are not rated by a lockup %. Because of the internal gear mesh design versus friction discs (of the clutch type LSD), there is zero slip, but it does not function like a 100% locked spool - since the wheels can still spin at different speeds. And they are basically open when unloaded.
10-23-2007, 11:50 AM
#6
Nordschleife Master
In my opinion/experience, a 20/100 locking differential produces too much understeer on turn in as the rears are locked 100% and try to push the car straight. In addition, under acceleration, the 20% seems to allow too much wheel spin on the inside wheel. So, I would rule out the 20/100, 22/40, 25/65. I am running a 40/65 motorsport and it seems fine and I would imagine that the 50/80 would also be fine. I'm not sure the benefit of running an 80/80, but I haven't tried either of those and cannot comment.
10-23-2007, 01:00 PM
#7
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In my opinion/experience, a 20/100 locking differential produces too much understeer on turn in as the rears are locked 100% and try to push the car straight. In addition, under acceleration, the 20% seems to allow too much wheel spin on the inside wheel. So, I would rule out the 20/100, 22/40, 25/65. I am running a 40/65 motorsport and it seems fine and I would imagine that the 50/80 would also be fine. I'm not sure the benefit of running an 80/80, but I haven't tried either of those and cannot comment.
R+C
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10-23-2007, 01:30 PM
#8
Dave I answered your PM but for the rest of the group...
I'm running a 50/80 setup from Gaurds Transmssion and really like the way it has improved the ability to get out of a corner and use all of my available low end torque not to mention keeping the car better planted in threshold braking situations. I was told that using 100% lockup for deceleration will make it more difficult to carry the braking into the turn. Some pro teams do use it in certain situations but since I'm not at that level I felt this was the best comprimise.
I'm running a 50/80 setup from Gaurds Transmssion and really like the way it has improved the ability to get out of a corner and use all of my available low end torque not to mention keeping the car better planted in threshold braking situations. I was told that using 100% lockup for deceleration will make it more difficult to carry the braking into the turn. Some pro teams do use it in certain situations but since I'm not at that level I felt this was the best comprimise.
10-23-2007, 02:21 PM
#9
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Remember that the degree of lockup is a function of input torque as well as the characteristics of the differential (in most cases).
So a diff with 40/65 ramps actually locks up much harder under acceleration than it does on deceleration. This also means that by using a different gear in a given corner (especially on entry), you are changing the input torque and hence the lockup.
Downshifting to the lowest possible gear generates the highest possible degree of lockup, which may or may not be desireble.
Chris Cervelli
Spline Technologies
So a diff with 40/65 ramps actually locks up much harder under acceleration than it does on deceleration. This also means that by using a different gear in a given corner (especially on entry), you are changing the input torque and hence the lockup.
Downshifting to the lowest possible gear generates the highest possible degree of lockup, which may or may not be desireble.
Chris Cervelli
Spline Technologies
10-23-2007, 05:32 PM
#10
Rennlist Member
Downshifting to the lowest possible gear generates the highest possible degree of lockup, which may or may not be desireble.
10-23-2007, 05:38 PM
#11
Race Director
I believe it what he is say although.... Their may be times you DON'T want or need the extra stability. I believe Chris's point is with an LSD you use which gear you are in to adjust on the fly how the diff responds. Pretty cool stuff.
10-23-2007, 05:52 PM
#12
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Yeah, it depends on what problem you have having in the corner entry.
If the car won't turn in aggressively enough, then using the higher gear gives less lockup and less anti-yaw.
Conversely, if the car is extra loose on entry, then the lower gear gives more lockup and more anti-yaw. On the other end, the extra drag from the engine is like more rear brake bias, which is likely to cause even more oversteer.
In acceleration, you have to choose the gear that gets you closest to the traction limit out of the corner. Otherwise what the diff is doing is irrelevant because you are exiting the corner too slow.
Chris Cervelli
Spline Technologies
If the car won't turn in aggressively enough, then using the higher gear gives less lockup and less anti-yaw.
Conversely, if the car is extra loose on entry, then the lower gear gives more lockup and more anti-yaw. On the other end, the extra drag from the engine is like more rear brake bias, which is likely to cause even more oversteer.
In acceleration, you have to choose the gear that gets you closest to the traction limit out of the corner. Otherwise what the diff is doing is irrelevant because you are exiting the corner too slow.
Chris Cervelli
Spline Technologies
01-25-2017, 10:08 AM
#14
Rennlist Member
It's a thrust washer that sits between the case and the side gears. Sources would be Porsche or Guard Transmission.
