[tke743]

Alright, after an afternoon of the true drudgery of sliding 2 m235i’s around with LSD’s, here is our result.
E-Diff – Already reviewed in OP

M-PERFORMANCE LSD
Eco-pro – STILL boring, hate it, nuf said.

Comfort - soft, smooth, cruising mode. Nanny heaven. Minimal discernible difference from the e-diff. Nannys kick in too soon. No discernible difference between the 2 LSD’s.

Sport - it is just comfort mode with firmer suspension along with exaggerated inputs on throttle and steering, plus the slightest lag in the nannys taking the fun away. With the M-Performance LSD, the LSD will actually kick in before the nannys, so you can push a bit harder then without it. Adds a little more fun, but there is not enough difference to justify the cost. No discernible difference between the 2 LSD’s.

Sport+ - It is sport, nanny lag is increased to approximately .5 sec of stupidity, then it kicks in hard with the nanny regimen. And this is where the LSD starts to earn it’s keep. The LSD kicks in before the nannys get a chance, if you are driving at or near (or slightly over) the limits of grip the nannys will stay in the back seat unlike with the stock diff. If you are trying to drift it, then the nannys are still there to take over. Little difference between the 2 LSD’s (this will be discussed in the summary).

DSC OFF - My favorite mode (not for day to day driving where the nannys have their place, especially on these roads.) No nanny kick in, just the e-diff. Does not have the exaggerated throttle and steering but keeps the suspension tight. I prefer the lack of the exaggeration, I don't need fake enhancements, and I tell the car when to shift. This is where the 2 LSD’s show their stuff and show the difference from the e-diff (which is definitely still there.) The M-Performance LSD is just quicker than the e-diff and keeps the rear end stable in all situations. On heavy power it does its job. Very well sorted, but different from the Quaife (this will be discussed in the summary).

Pre Corner off throttle (DSC OFF) – This is a major improvement on deceleration. Wow, the 9% lock is felt, and the chassis is much more stable on the off throttle event then the stock pumpkin. (Note that the e-diff is adding to the 9%, because this is in no way a simple 9% locker.)

Starting on ice – Works as you would expect. You just pull away. Slight advantage from the e-diff, but it is a $50 improvement, not a $3k improvement.

QUAIFE

Eco-pro -STILL boring, hate it, nuf said.

Comfort - soft, smooth, cruising mode. Nanny heaven. Minimal discernible difference from the e-diff. Nannys kick in too soon.

Sport - it is just comfort mode with firmer suspension along with exaggerated inputs on throttle and steering, plus the slightest lag in the nannys taking the fun away. With the Quaife LSD, the LSD will actually kick in before the nannys, so you can push a bit harder then without it. Adds a little more fun, but there is not enough difference to justify the cost.

Sport+ - It is sport, nanny lag is increased to approximately .5 sec of stupidity, then it kicks in hard with the nanny regimen. And this is where the LSD starts to earn it’s keep. The LSD kicks in before the nannys get a chance, if you are driving at or near (or slightly over) the limits of grip the nannys will stay in the back seat unlike with the stock diff. If you are trying to drift it, then the nannys are still there to take over. Little difference between the 2 LSD’s (this will be discussed in the summary).

DSC OFF - My favorite mode (not for day to day driving where the nannys have their place, especially on these roads.) No nanny kick in, just the e-diff. Does not have the exaggerated throttle and steering but keeps the suspension tight. I prefer the lack of the exaggeration, I don't need fake enhancements, and I tell the car when to shift. This is where the 2 LSD’s show their stuff and show the difference from the e-diff (which is definitely still there.) The Quaife LSD is just quicker than the e-diff (And the M-performance LSD) and keeps the rear end stable in all power on situations. On heavy power it does its job. Great pumpkin, but different from the M-Performance (this will be discussed in the summary).

Pre Corner off throttle (DSC OFF) – This thing is an open diff on deceleration. The chassis gets skittish on the off throttle event just like the stock open diff.

Starting on ice – Slight advantage from the e-diff, but it is a $50 improvement, not a $3k improvement. (Note: We tested the infamous 0 traction on one wheel start too, the e-diff kicks in and this slight hypothetical limitation of the Quaife disappears. Even when there is 0% traction on a single wheel the e-diff adds resistance and off you go.)

Summary.
If you are looking for an LSD for bad weather traction or for hard driving up to, and including, a single track day per year, don’t bother. The E-diff is actually quite good.

If you are still fretting about that 1/10 th of a second you left in corner 5 during your third track day last summer (I am) then LSD is for you. Then it comes down to which one.

Here is the summary of the breakdown between the LSD’s

M-Performance – This is a mechanical (clutch type) 30% locker on acceleration, but the electronics on the M235i were obviously designed to work with this specific pumpkin. There is no way that in the real world that this is a 30% lock, the electronics are assisting it and my guess is that it is over 40% in practice. On power it is very good as a combination, but the Quaife is better on throttle.
Then there is off throttle. The M-Performance LSD is a 9% locker, but the electronics help it here too. There is no way this is just 9% in real world situations. What it does on the hard into a corner off throttle stabilization is amazing. It changes the car. There is a reason that road racers use 1.5 way LSD’s. (And 2.0 way LSD’s if not streeting the car.)

Quaife – This is a gear type LSD and has almost 100% transfer available on acceleration. Flat out it is quicker to adjust than the M-performance LSD on throttle and it is so quick that it adjusts before the car tries to help further.
The issue is that off throttle it does nothing. It is just like the stock open pumpkin when you lift the right pedal.

Final Summary-
Again, for basic street driving, aggressive street driving, track day novice and bad weather, don’t bother. The e-diff is quite good.

Now for the fun summary
Buy the M-performance if you are road racing, autoX, anything where the chassis dynamics needs to be at its best entering the corner. It is 95% as good as the Quaife on throttle, but MUCH better in other situations.

Buy the Quaife if you are drifting, drag racing, want massive (but amazingly controllable) oversteer or you are a hooligan. It is just flat out better on throttle. But if you are looking for 0.1ths of a second on a track, the M-performance will be better.

We both tested without sharing notes until done, we both fully agreed on these assessments. Incidentally, he likes drifting, and dragging and I race, so we are happy with our choices even though we acknowledge the other LSD’s strengths and realize there is no perfect choice.

Alright my $0.02 given.

p.s. I did not consider maintenance as part of this, only performance. I know that the M-Performance will need maintenance at or before 50k miles. I know the Quaife will be bulletproof and still in existence when the sun explodes. That is not what I was testing.