csmarx

We all the know the issues with the GT3 LSD's - in particular the 997 GT3 with it's weak 28/40 lock ratios and internals that might not bite when they should.

Does anyone know what the 991 GT3 LSD is going to be or if there even is one, what with PDK, TC, PSM, and 4 wheel steering?

Thanks,
-Christian

Petevb

The 991 is getting an electronically controlled LSD of a very different design than previous units.

Mike in CA

The old LSD with fixed locking ratios is history. The new LSD is constantly variable and electronically controlled. It's hydraulically operated by a pump driven off of the PDK-S gearbox.

Edit: posted before I saw Pete's response above.

csmarx

Ah, that's right, it's getting an eDiff ala the Fezza's et al. I did read that. I'd still like to know more about how it functions though.

Thanks,
-Christian

CAlexio

Is this like a viscous coupling? Does it being "infinitely variable" make it stronger? Ill google this but interested in hearing more from those in the know. And the best part is we can now stop talking about contrasting stitching options

csmarx

It doesn't seem to get as much press as the RWS, and increased wheel base, but surely the eDiff is a huge part of the improved handling of the car?

Mike in CA

Porsche says that it's a big part of the handling improvement under all conditions. Even under braking, unlike a mechanical diff, the e-diff is able to completely release the locking effect which allows ABS to operate optimally on individual wheels.

neanicu

Yes...
It is also the reason a manual transmission is not offered
It would've been too difficult to design a pump for the e-diff. This explanation belongs to AP and it is to be believed by little kids waiting for Santa...

frayed

I think it's been underplayed considerably. Everyone is pointing to RWS as the reason why the new rig turns in so well. I don't think this is the case: it's the ediff. A fully open diff at turn-in and fully locked when you put the loud pedal down. Great stuff. . . ala fezza indeed.

The ediffs in the modern fiats are said to be the reason they are so predictable at the limit, unlike past fiats.

RWS is getting all the attention b/c it's a novelty.

----------------------------------------------

BTW, the 458 came with a manual transmission as an option along with ediff, b/c the pump is external to the gearbox. So, I agree with Rad's prior statement that it's a bit of a cop-out when AP says that a MT car can't have ediff b/c the pump is in the PDK gearbox.

Petevb

A gear type LSD is also open on decel/ turn in. There must be more to the E Diff operation.

frayed

gotchya, but no full lock correct?

Petevb

Correct, not fully locked.

Mike in CA

Porsche states:

Another advantage is improved braking behaviour when full braking is required and a complete release of the rear-differential lock enables optimal actuation of the individual wheels during ABS braking, resulting in stable and efficient braking with maximum deceleration.

I don't doubt your statement, so is Porsche touting an "advantage" that isn't really an advantage?

Petevb

I think Porsche marketing is trying to boil the real advantage the E diff gives down to a simple soundbite that the consumer can understand... I suspect that the diff operation is actually pretty complex, perhaps taking lateral Gs, speeds, etc into account when deciding when to lock and unlock.

A gear type diff is open when it's decelerating or not under power. This is good for turn-in, especially into tight corners, which is why it's favored in autocross. Being open in decel, however, is considered a disadvantage for big track work, where a plate type locking diff adds stability during higher speed turn-in.

Having the diff electronically actuated will allow Porsche to tune when it's active or not, perhaps unlocking it at lower speeds when maneuverability is required and locking it at higher speed when you need stability. Or perhaps they have tuned the ABS or RWS to add some of that stability. I'm not sure, but having it electronically actuated gives them a bunch of new options to tune the handling, and I suspect they are taking advantage of them.

roberga

Oh no- not PDK again. Another reason no MT. Integrated systems communicating. Funny I just put electronic system on my bike. I love down tube shifters of the olden days and take out #3 for retro TT and fun rides. but like PDK electronic shifting is the here and is the future.I am sure some bike ride thinks only a ***** would not rather use old friction shifters. It does however enable one to find different ways to extract speed and enjoyment. Hopefully the PDK will provide the same.