Glen is pretty well spot on IMO. I have three different types of LSD in 3 different cars, and two of them initially had open diffs. The helical/torsen style will lock as long as both wheels have some resistance, and they last nearly forever. I suspect that reliability and "good manners" is why they are put in the road cars. The clutch types do best at locking, react the quickest, but the clutches wear. I suspect this is why they are chosen for race applications--best performance, and rebuilding the diff is just one of the many additional high maintenance items that people put up with because racecar. The viscous doesn't lock so well, seems to hold up better than a lot of what I've read on the intarwebs, but since Lotus doesn't use these I'll just say it feels weird sometimes at the limit and now I will shut up about that.
A 1.5 or 2 way would seem to have a bit more of that bind mid turn that Glen is referencing, but I honestly don't think there is much restriction in the turn in. My BMW has a 1.5 way clutch style LSD. It can be noisy at low speeds--not ridiculous loud, just kind of disconcerting if you don't know what it is. I never hear it when flogging the car because the motor/exhaust is louder, but for instance in a parking lot you can hear the diff when turning tightly. I've got a ton of miles on this car and I'm sure it's not doing its job as well as it once was. It's one of those things that gradually fades so you don't really notice it "going bad" but if I were to rebuild/replace it I bet I would see a noticeable improvement.
My Lotus came with no LSD and I added the TRD unit later, so I can give a direct comparison there. On the street, there is no discernable difference as I'm not going to push the car to the limits. In autocross, I don't feel a difference regarding turn in, but it's obviously different for putting the power down. Since there are lots of "digging out of corners" in autocross, there are plenty of opportunities to spin the inside wheel for just a bit, and in a sport where we are worried about .1 of a second, it really can make a difference to be able to put the power down just a few feet sooner. The same is true when pulling out of a corner on a road course, but I think the percentage of relevance to overall lap/run time is highest in autocrossing.
Personally I prefer the helical as I feel it provides both performance and low maintenance reliability.
Last edited by Parko; 11-16-2017 at 07:41 PM.