Does an LSD make a difference?
Discussion
I would never entertain something like a C63 with no LSD as it would just be a frustrating handful, the same goes for any other high powered car with traction issues.
I don't have an LSD in my Cayman though and I can't say I miss it. I never have any issues with traction, and when I'm mucking about it will come sideways out of a junction nicely and it does a decent doughnut too.
So would I really notice a difference with the factory fitted one? I've the internet is to be believed the mechanicals inside wear out very quickly and it stops being an LSD and starts becoming a regular open diff after 25,000 miles.
If you were in the market for a Porsche would a LSD be high on the list of requirements?
I don't have an LSD in my Cayman though and I can't say I miss it. I never have any issues with traction, and when I'm mucking about it will come sideways out of a junction nicely and it does a decent doughnut too.
So would I really notice a difference with the factory fitted one? I've the internet is to be believed the mechanicals inside wear out very quickly and it stops being an LSD and starts becoming a regular open diff after 25,000 miles.
If you were in the market for a Porsche would a LSD be high on the list of requirements?
This might seem heresy, but I prefer the feel of my 987.1 Cayman S on 18s and with PASM to the 987.2 Cayman R over an hour's spirited test drive.
I think my own car has less understeer and more granular steering feel. The differences are relatively minor though, and the Cayman R had better traction on corner exit.
I think my own car has less understeer and more granular steering feel. The differences are relatively minor though, and the Cayman R had better traction on corner exit.
Personally I don't think the Boxster/Cayman are powerful (torquey) enough to need an LSD in normal driving. My 981 has only once spun an inside wheel and that was making a hasty right turn off a Give Way line in the rain.
LSD has more of a place on powerful turbo cars where the surge of torque can upset things.
LSD has more of a place on powerful turbo cars where the surge of torque can upset things.
Most people think that a limited slip diff is only useful on exit of a corner but it is actually very helpful under braking as it helps settle the rear of the car - especially if you are trail braking.
If you like to explore tfull performance I would say that a limited slip diff was pretty much an essential option
If you like to explore tfull performance I would say that a limited slip diff was pretty much an essential option
I have a wavetrack “LSD” in my 996 turbo, to me it makes a huge difference for competition type driving. On the road only I would say the normal PSM set up will suffice and of course it has a front diff to assist forward movement.
I like to be able to steer the car with the throttle as well as the steering wheel, the standard brake assisted system will prevent this, albeit it does make the car super safe.
For example, at a VERY wet and slippy Wiscombe Park earlier this year for one practise run I left the PSM on, car was safe but every time I pushed on it was like a giant hand pushing down on the car slowing it down with dual controls and someone else on the brakes and ignition!
Next run turned it off as I always do, almost 4 second faster but the cars moves around quite a bit.
Traction is much better, turn in as well, and as Steve says, if you heel and toe correctly you can brake a lot later with more stability, so yes, IMO an LSD is a big improvement.
Mine does have around 580 torques though
I like to be able to steer the car with the throttle as well as the steering wheel, the standard brake assisted system will prevent this, albeit it does make the car super safe.
For example, at a VERY wet and slippy Wiscombe Park earlier this year for one practise run I left the PSM on, car was safe but every time I pushed on it was like a giant hand pushing down on the car slowing it down with dual controls and someone else on the brakes and ignition!
Next run turned it off as I always do, almost 4 second faster but the cars moves around quite a bit.
Traction is much better, turn in as well, and as Steve says, if you heel and toe correctly you can brake a lot later with more stability, so yes, IMO an LSD is a big improvement.
Mine does have around 580 torques though
Steve Rance said:
Most people think that a limited slip diff is only useful on exit of a corner but it is actually very helpful under braking as it helps settle the rear of the car - especially if you are trail braking.
If you like to explore tfull performance I would say that a limited slip diff was pretty much an essential option
Interesting that re stability under brakes. How would that work though on a car with one of the variable locking ratio diffs that everyone seems to be using these days (458/991 gt3/sls black etc) rather than the older fixed ratio diffs as I think I had read somewhere (perhaps mistakenly!) that it was supposed to give an advantage over the fixed ratio diff being able to go from 0% under brakes/off throttle to 100% lock under power.If you like to explore tfull performance I would say that a limited slip diff was pretty much an essential option
For me it was an absolute no-compromise item when buying my 951 and I don't regret it for a second. Mine has now done 119k without (to my knowledge) a rebuild and is still completely effective and it adds a huge amount to the driving experience. But then my car is driven how Porsche intended... If you're just buying a car to drive well below it's limits then you're wasting your time. It all depends on how hard you drive the car and IMO.
The ZF plate diffs will inevitably require a rebuild at some point, but I think they're far longer lasting than some people would have you believe. Don't confuse these with the viscous type diffs found in many Japanese performance cars; the VLSD in my 60k Impreza STI is pretty much completely open so on track I can get a fair bit of wheel spin.
On aftermarket Torsen diffs: these are a definite upgrade over an open diff but they can feel very inconsistent in their operation, where a plate type diff offers a more stable and consistent locking action which I believe is very important on a RWD car.
The ZF plate diffs will inevitably require a rebuild at some point, but I think they're far longer lasting than some people would have you believe. Don't confuse these with the viscous type diffs found in many Japanese performance cars; the VLSD in my 60k Impreza STI is pretty much completely open so on track I can get a fair bit of wheel spin.
On aftermarket Torsen diffs: these are a definite upgrade over an open diff but they can feel very inconsistent in their operation, where a plate type diff offers a more stable and consistent locking action which I believe is very important on a RWD car.
Apologies for going slightly off-topic...
All the Impreza STI starting in 2007 as well as the rear of the Legacy Spec B (6MT version) have Torsen® T-2 type LSD in the rear.
Richair said:
Don't confuse these with the viscous type diffs found in many Japanese performance cars; the VLSD in my 60k Impreza STI is pretty much completely open so on track I can get a fair bit of wheel spin.
I assume your STI is pre 2007? Or are you talking about the front diff?All the Impreza STI starting in 2007 as well as the rear of the Legacy Spec B (6MT version) have Torsen® T-2 type LSD in the rear.
It seems there are both pros and cons,
"Lotus reluctantly added LSD to their option list to satisfy US buyers who wanted to autocross the car; Lotus engineers claimed they were faster around racetracks with an open diff.
"The guy who ran the design team was at LOG 26 and gave a talk. It was interesting. That's what he said about the LSD. He also said that customers buy them and think they are going to make them faster with all these mods, but anything they do makes them slower. However, if the customer is more comfortable with the car set up that way, it may be faster for him."
"Lotus reluctantly added LSD to their option list to satisfy US buyers who wanted to autocross the car; Lotus engineers claimed they were faster around racetracks with an open diff.
"The guy who ran the design team was at LOG 26 and gave a talk. It was interesting. That's what he said about the LSD. He also said that customers buy them and think they are going to make them faster with all these mods, but anything they do makes them slower. However, if the customer is more comfortable with the car set up that way, it may be faster for him."
I looked into this a while back and the consensus from people who had taken a Porsche standard LSD apart was that it had very limited locking function and would wear and (and become an open diff) after fairly minimal hard usage.
I regard them as largely fashion items in any NA Porsche.
I regard them as largely fashion items in any NA Porsche.
isaldiri said:
Steve Rance said:
Most people think that a limited slip diff is only useful on exit of a corner but it is actually very helpful under braking as it helps settle the rear of the car - especially if you are trail braking.
If you like to explore tfull performance I would say that a limited slip diff was pretty much an essential option
Interesting that re stability under brakes. How would that work though on a car with one of the variable locking ratio diffs that everyone seems to be using these days (458/991 gt3/sls black etc) rather than the older fixed ratio diffs as I think I had read somewhere (perhaps mistakenly!) that it was supposed to give an advantage over the fixed ratio diff being able to go from 0% under brakes/off throttle to 100% lock under power.If you like to explore tfull performance I would say that a limited slip diff was pretty much an essential option
The behaviour on the brakes/power application and 'how' the diff locks up are a function of ramp angles and preload on the plates, so you can tune the diff to achieve whatever you want. The Ferrari/Lambo "e-diffs" give you various diff setups depending on the mode selection in the cabin. Not sure of the process of how they get the diff to do this though. Some of the effects of LSD can be mimicked via application of the rear brakes (through the ABS/Diff ECU).
I do not like electronic diff set ups via an abs ecu. A chap needs to know that when he applies his brakes they will all be working at 100% efficiency and not being applied and/or re applied on different wheels without his knowledge. This makes for unpredictable behaviour when the car is fully loaded. Its the same set up on my 997GT3 which has a mechanical diff made of chocolate and an ABD system which cuts in as a back up when the mechanical diff is worn out which is generally the first time that I reversed the car out of the garage. ABD is also a rotational aid to the driver making it less neccessary to trail into the corner as the abd is already rotating the car for you - which is just as well because if you do try and trail in, there is a good chance that the abd system will help you in your journey straight into the barriers. Porsche have now done with this method of interference as a rotational aid and took things to the next level by lenthening the wheelbase of the 991 thus making it more stable in fast corners and adding a rear wheel steer system which pretty much handles everything else.
Variable diffs/ electronic diff aids are fine until a driver starts to get near to threashold, then they become just another variable control adjustment that the car does without the driver's knowledge, interfering with his own imputs and generally making the car a whole lot more difficult to predict. One should not be required to predict what a car might do, it is rather like closing the stable door after the horse has bolted. It is far better to act on information provided by rather than acted upon by the chasis. That way he may react to - rather than try to predict a car's behaviour.
Give me a mechanical diff any day
Variable diffs/ electronic diff aids are fine until a driver starts to get near to threashold, then they become just another variable control adjustment that the car does without the driver's knowledge, interfering with his own imputs and generally making the car a whole lot more difficult to predict. One should not be required to predict what a car might do, it is rather like closing the stable door after the horse has bolted. It is far better to act on information provided by rather than acted upon by the chasis. That way he may react to - rather than try to predict a car's behaviour.
Give me a mechanical diff any day
fergus said:
The behaviour on the brakes/power application and 'how' the diff locks up are a function of ramp angles and preload on the plates, so you can tune the diff to achieve whatever you want. The Ferrari/Lambo "e-diffs" give you various diff setups depending on the mode selection in the cabin. Not sure of the process of how they get the diff to do this though. Some of the effects of LSD can be mimicked via application of the rear brakes (through the ABS/Diff ECU).
I thought the variable ratio diffs was one that was electronically controlled to adjust the locking ratios depending on sensor input as required rather than simply preset the locking ratio according to the driving mode selection? same as in the 991 gt3.http://rennlist.com/forums/991-gt3-and-rs/849272-a...
Orangecurry said:
Apologies for going slightly off-topic...
All the Impreza STI starting in 2007 as well as the rear of the Legacy Spec B (6MT version) have Torsen® T-2 type LSD in the rear.
Rear diff and mine's a 1995 version 2 STI wagon so is open front and vsld at the rear. Proper diffs were only fitted to the STI RA and other special classics from memory...Richair said:
Don't confuse these with the viscous type diffs found in many Japanese performance cars; the VLSD in my 60k Impreza STI is pretty much completely open so on track I can get a fair bit of wheel spin.
I assume your STI is pre 2007? Or are you talking about the front diff?All the Impreza STI starting in 2007 as well as the rear of the Legacy Spec B (6MT version) have Torsen® T-2 type LSD in the rear.
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