Quote:
Originally Posted by Biginboca
Let’s that in Pete’s example his car had an open diff the lap time might have been 100 seconds. He had Ediff added his lap time is now 96 seconds. Now he adds LSD his lap time is 90 seconds. The Ediff is serving a function and not slowing him down! It’s just not as good as a LSD but no ones saying it is.
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I'm sorry but the thing that you, and the others who try to defend the e-diff, continue to want to ignore is that the e-diff doesn't always work the way it's programmed to like in a perfect world. E-diff can absolutely be slower around a corner than an open diff. I am not qualified, and neither are you by the looks of it, to try to explain it. There are cars that lap faster than a e8x/e9x that have open diffs. I've ran my 135i with an open diff. My lap times were actually pretty much dead on consistent with the e-diff lap times and possibly 1s faster at LimeRock (hard to tell such a small difference). The car felt different for sure (more predictable/smooth I dare say?). Running an open diff is not a problem if you've got the mechanical grip and you know how to use your right foot properly (I also have linear throttle mapping instead of BMWs 80% throttle at 20% input).
The e-diff programming is designed to keep the rear-end in check... it's not designed for taking sharp turns on-power. E-diff is trail braking through turns due to wheel speed differences even in situations where both tires are still providing adequate Mechanical grip. A mechanical LSD operates as an open-diff while cornering until resistance changes (NOT wheel speed like the e-diff)... Just because two wheels are spinning at different speeds does not mean you need to slow one of them down. Also, the e-diff begins applying the brakes before the slip ever happens. That's an example of unwarranted loss that slows the cars acceleration and/or robs power.
Also, any differential adds drivetrain loss vs an open diff. If you don't have traction loss all this lsd babble is a moot point (again, even a mechanical diff operates as an "open-diff" while cornering). You keep bringing up 200rpm in/2 rotations out... But then ignoring that the frictional loss of ANY lsd means you won't be getting 200rpm in anymore since there is more drive-train loss. The motor can only provide a finite amount of torque.
Another consideration is that the e-diff might actually measure ALL 4 WHEEL SPEEDS. Meaning, the e-diff can, and will, influence full-on drifts by reducing power output (if what I am saying is true). I say this because of what I've experienced at dyno sessions... Ever taken an e-diff equipped car to a dyno? Even if you disable all traction control, the car will not run on a dyno properly. It takes a few minutes for the car (e-diff) to FREAK OUT enough about the rear wheels spinning faster than the fronts before the car THROWS A MECHANICAL FAULT and completely disables ABS/E-diff (Trifecta lights on the dash). So yes, based on this theory, the e-diff slows down full-on drifts to "keep them in check" to a certain degree before it fails altogether. After leaving a dyno session you need to clear abs faults to get your e-diff/abs back (you will have the trifecta lights on the dash). Also, my 135i has massive torque that SHOULD be adequate enough for doing burnouts, yet when trying to do a full-on drift the car BOGS. The only time people seem to get these cars to drift is in the rain and yet even at 450wtq the car seems to barely be able to sustain that drift (all that braking being applied).
The e-diff is also most likely tied into the yaw sensor. It uses the cars yaw rate to apply it's preemptive brake force. However, a tuned car can easily see a greater yaw rate than a factory car without losing mechanical grip. Again, another example of how e-diff slows the car down (it's predictive braking).
A lot of what I just said is speculation (none of us know how e-diff programming looks), but the e-diff does cause the car to feel funky at times. I've seen the car burn up the left tire and then 2 seconds later the opposite tire is lighting up. That's the e-diff trying to balance the torque through the application of the brakes. It's doesn't work right sometimes plain and simple... Rcomps need a bit of slip at times and produced mechanical grip at significantly greater slip angles than a street tire... track pads have significantly different friction coefficients depending on temperature... These are variables that the e-diffs programming were not designed around.
If you still don't understand what we are trying to say, read this:
http://www.houseofthud.com/differentials.htm
The "EDL (often referred to as Electronic Traction Control)" and the "So why use EDL if it's so bad?" sections explain the issues pretty well (the same issues many people are trying to point out here).