wamara

I need some education here. I see that the optional Z51 package includes an "electronic limited slip" differential, while the standard car is fitted with a (presumably mechanical ??) limited slip differential. Assuming my presumption is correct, can someone explain the pros (and cons, if any) of the electronic versus the standard diff ?? Do these function completely different than a Torsen ?? Thanks.

Kappa

eLSD is mechanical but controlled by the computer according to throttle, yaw, brake, and steering inputs. It can go from 0% to 100% lock and everywhere in between in a very short amount of time.

So basically you get an open diff for straight line and fast turn in, and the LSD for through and out of the corner work. Should be great judging by the results other cars have had with it.

RC000E

Both are viscous clutch type lsd's...one just uses electronic intervention to go from lock to unlock and everywhere between. The base mechanical unit just works like a traditional viscous lsd...as torque is applied, the lsd engages, when you let off, it disengages.

theseal

neither are viscous. the c6 and most all other vettes use a friction based clutch pack. they are spring loaded on c3-6, and apparently on the base c7 as well.

they work pretty well, though certainly under high drop throttle torque they potentially reduce rear grip or otherwise affect handling on turn in.

a torsen type differential is ideal, especially a t2r type, which has very limited interference on turn in or drop throttle, but excellent and immediate torque distribution on acceleration.

i expect the e diff to be unnoticed by most street drivers, very 'ok' for most very amateur drivers on a road coarse, and be a source of tremendous frustration to anyone who is a good driver and wishes to track the car.

while F1 level tech and software tuning customized for each driver, on each track, on each particular day can make a diff work a bit better than a torsen, any factory tuned setup will likely be much worse than a torsen would have been (or even the clutch pack), and more expensive to build, operate, and maintain to boot.

Sin City

Let's see... I can type a letter on a mechanical typewriter -- or I can use a computer with a word processor.

Which is better? Hmmmmm.

I think the electronic version. I can edit, add photos, do spell check, save it, email it, put it different formats, use different type faces, print it over and over again, etc, etc.

Both produce a letter. One does it better, easier, and more efficiently.

Same for Ediff. It's tied into the other systems and acts intelligently instead of just doing it's job dumbly.

ZL-1

The e-dif components were on display at the Bash. At first glance it looked like a big weight penalty. But considering that the big part that goes inside the axle takes the place of the mechanical LSD that would otherwise be there, the weight gain would be pretty much limited to the electric motor and pump, lines, module, wiring harness, and extra fluid.

JoesC5

If I'm coming out of a tight corner in first gear at 30 MPH, pulling 1g, and I go WOT for a short stretch and I light up the rear tires because I have 450whp and am running at the very edge of the traction capabilities of my tires; what will the eLSD do that the mechanical differential doesn't do to keep me from doing a 360 spinout?

JoesC5

The eLSD appears to have hydraulic cylinders instead of springs to provide clamping force to the discs.

Thrl_skr

eLSD is a huge improvement over the non-Z51. Importantly, an eLSD is an area that the aftermarket will not offer a suitable upgrade if you choose to go with the base model and want to upgrade.

Many makes refer to active yaw control in one form or another and have a mechanical LSD, but use the braking of one wheel to affect yaw. We're fortunate that GM went the eLSD route...Porsche will follow suit eventually. In my mind, eLSD > individual wheel braking to maintain or enhance balance.

rcallen484

WOT in first at 30mph? No tire that will fit in a C6 or C7 wouldn't be beyond its traction capabilities and spinning.

Thrl_skr

As you know an LSD doesn't perform miracles. Versus a clutch pack or torsen, you should expect better turn-in coming into that tight corner and you'll be able to apply --not stab-- throttle sooner without going wide coming out.

JoesC5

That was my point. What does the eLSD give me that replaces drivers skill. I come out of that corner with my old fashioned differential and I give it just enough throttle for maximum acceleration without lighting up the tires. If both rear tires are spinning because I give it too much throttle(and not even WOT), what does the eLSD do to prevent it? I see that it does nothing, especially on the street, where getting to the Golden Coral 3 seconds earlier isn't going to matter(unless I'm running late for the early Bird Special that stops at 4 PM).

JoesC5

How is that? I don't normally go with more throttle(more likely to be on the brakes) entering a corner but give it more throttle coming out of a corner. I don't normally spin the tires while braking with zero throttle application.

Thrl_skr

I agree with much of what you wrote; however a torsen has limitations. One very relevant limitation. When one wheel had zero traction the diff sends all the torque to the wheel without grip! This is more common than it seems, like running over the striped curbs at the track.

theseal

BMW (and maybe porsche? i dont know but would be shocked) has gone to the lazy and grossly negligent practice of using open differentials, and just using the abs to prevent wheelspin. Absolute horror. that is not what is going on here.

the e diff is not grossly negligent by design; with proper software tuning, and fast enough mechanical linkage it COULD work, decently. but i seriously doubt it will be great. and almost certainly it will not work as well as a torsen.

in F1 they use e diffs; the drivers' timing on the gas matters down to the thousandth of a second when it comes to corner exit. The actuation in F1 is extremely fast, and yet the software still has to anticipate things to be right. They tune that sophisticated e diff carefully for each car, driver, tire, fuel load, surface condition, etc. it takes all this level of race day tuning to get this system to outperform a torsen.

torsens work extremely well. even clutch packs work pretty well, especially when you are tuning the engine management to prevent off throttle turn-in issues as the c5 and up cars do.

the vette's e diff has over a foot of hydraulic lines putting pressure on clutches. some marketing crap they put out was bragging on going from open to locked in several tenths of a second. in that amount of time you have already lost an autocross or competitive road race, just in one corner.

the e diff software will have to anticipate those reactions, and deal with best guess averages for driver inputs, style, and conditions of the road, tires, etc. it is not going to work as well as a torsen would have, i can pretty well promise you that.

i expect it will also be tuned to prevent yaw angle and in essence prevent a good driver from using the car properly both on corner entry and exit. in other words, this system is not intended by GM to be a better diff than they could put in the car mechanically; it is intended to be a better way to tune handling *against the driver's inputs* than by just using the abs and engine management alone. in other words; i believe time will tell that this system is supposed to be a nicer nanny, not really a performance differential upgrade.

theseal

that is true, that is why i mention the t2r, which has a mild tension to keep the gears engaged in that situation. it works really well and was huge benefit to the solid axle cars it was popular for, but the vettes did not have enough market or need for it so it was not a common upgrade as the independent rear works pretty well as is, and a torsen is not real cheap.

Thrl_skr

Gotcha. I wasn't aware of that revision; it's been awhile since I've used a torsen. That's a nice upgrade.

ck9887

My IS-F has an ELSD. Not sure how similar it will be to the C7 setup but during hard track driving, the ELSD can't quite keep up. I can actually feel it working but it's always a split second to slow before it will lock up. Many of the IS-F guys upgrade to a true mechanical diff.

So let's hope the C7 ELSD is track worthy.

Thrl_skr

Sorry, I missed your post as I was responding to another. An LSD doesn't just impact the vehicle when under throttle. This has nothing to so with spinning the tires with zero throttle. A differential allows the inside and outside wheels to travel a different speeds. An eLSD allows a completely open (decoupled) upon turn in whereas a traditional LSD would still be partially engaged. It's a finesse thing, and will likely allow you to carry more speed into and out of the corner.

Thrl_skr

Ewww....that sounds awful. Is it a hydraulic unit too? Based on this link it sounds like it isn't comparable. http://blog.caranddriver.com/lexus-i...eels-for-2010/

Not being a fan, I only searched for a second. A better comparable is probably the rear diff on an Evo X (my winter beater). http://en.m.wikipedia.org/wiki/Active_Yaw_Control