Torsen LSD;
See this first http://members.aol.com/solomiata/miataCSP.html

1/ fitted to 1.8iS Mk2 cars .. find one, strip gears off it (wrong ratio) and reset back lash... this is the easiest method .. but I have not found one of these cars in a Breaker yard yet....
2/ Get one from Jay .. who already has 3 waiting for one .. from Japan
3/ RX-7 TORSEN-1 from MazdaTrix will bolt right in. You'll want new side bearings and will need to have them pressed on. MZTX-TORSEN1.....DIFF TORSEN LSD....84-92 NON-TURBO...$ 762.95 = 476.85+50=680 in UK
4/. Mazda 1.8 Torsen MM02-27-200A = Torsen LSD = 657.14+VAT=772.14 in 6-8 weeks from UK dealer94 onwards LSD - might be MM02-27-200A= Torsen LSD
5/ Mazdaspeed clutch type LSD; needs special oil and not as sophisticated as Torsen in delivery
6/ Get one from a UK breaker .. I did after 8 months of hunting intermittently ... it is still sat on the floor in front of my car .. and needs a rebuild/tweak as they broke the outer cast iron housing :-( ... although this is not major work .. just engineering Blue, some special tools to make and a large vernier from work for the night! .. and the real tale behind this part is interesting ..it is the grandfather of the MGF diff .. came off a '95 Miata that Rover bought to evaluate while developing the MGF and then stuffed at 18,000 miles a few years ago...

then see www.quithel.co.uk\zz_Transmission.htm (2/00)

Nearly all UK spec cars have an open differential and no LSD. LSDs were additional cost items. A few special editions my have had them, but I'm not certain, I guess other list members will be able to help here. As you have a '93 there is only a viscous LSD or clutch type LSD that will fit the standard rear diff. housing, the viscous (most likely if there is one) will be OK with standard diff. oil, the clutch type will not. The only other possibility is that someone has put a 1.8L rear on the car, i.e. fitted the differential casing, halfshafts and propshaft from a 1.8L and then retro fitted a Torsen LSD into it, this is what I have done with my late '92. In this case also you would be OK putting in standard diff oil (I too have used redline 75/90).

There is no really convincing way to check for an LSD, perhaps best to look on the original dealer order form and/or if it's a limited edition check the specs. (4/00)

Not true on a Torsen LSD (as fitted to some 1.8 cars .. very few .. don't get excited!) ..

best way I have ... is spinning your wheels on tarmac .. if you spit hot rolls of rubber out of both wheels with heaps engine power you have a LSD!! .. but need mugs to stand behind to catch the rubber and a turbo/super....

.. so getting back to reality .. I would inspect inside the drain plug .. difficult but sort of fool proof .. the real way is to pull a driveshaft .. the Torsen has no 2mm pin across the hole through the middle of the diff. (4/00)

If you don't want to end up with teeth from your diff pinging about inside it listen for the telltale noises which came to me in this order:

Tick tick tick like a stone in your tyre, variable with speed
After the car warms up (10mins), I got an occasional alarming thrashing/clattering as though a bit of stiff wire was wrapped around the driveshaft (but never when I took it to a garage, tut!)
When the diff goes you *really* know that something scary has happened. (8/00)

Basically you have two extremes: -

"closed" diff: this would be the equivalent of a fixed axle between the left and right wheels. Not good because your wheels cover different distances in a turn. -

"open" diff: most used mechanical differential which allows the left and right wheel to turn at different speeds. It transfers all the power to the wheel with the least resistance (usually the one on the inside of the turn you're taking). The downside is that when a wheel starts spinning you lose all traction because the open differential sends all the power to that wheel since it has the least resistance.

And in between you have: - limited slip differential (LSD): allows wheels to turn at different speeds but limits the power difference between the wheels. Usually comes in two flavours:

+ viscous limited slip differential: limits the power difference between the wheels utilising a viscous liquid and two plates turning round in it.

+ torsen differential: pure mechanical solution to the problem.

There's an excellent site at: http://www.howstuffworks.com/differential.htm which explains differentials with quite some detail. (4/01)

Same q asked on the OC forum the other day - here's the same answer! :

Cars need a diff to enable the rear wheels to rotate at different speeds (from each other) eg when you're going round a corner (the outside wheel has to go further, therefore must rotate faster).

With an open (normal) diff, the design means that if a wheel loses grip, all the power is directed to that slipping/spinning wheel, and no power goes to the wheel which is stationary or moving more slowly. Not good for getting grip on a slippery surface (eg ice), but look at the situation if you're accelerating round a bend. Inside wheel loses grip, power removed from outside gripping wheel, so it won't lose grip and the back end will stay more or less in contact with the road, but you won't accelerate (because the power is being spun away uselessly). Unskilled drivers will stay in control. But if you're a skilled driver, driving for performance, you might want the outside wheel to provide grip so you can accelerate in this situation. Get it slightly wrong, though, and you'll put too much power to the one gripping wheel, it'll lose grip and you'll spin.

A limited slip diff allows this - it helps to provide some grip in very slippery conditions, and it helps a skilled driver to accelerate more quickly through a corner where the forces might be causing a wheel to loose grip. It also helps a less skilled driver to spin off in such circumstances. LSDs can make the car feel twitchy. You come across three types of LSD in MX-5s - early Roadsters often have viscous LSDs - these provide only a small amount of 'lock-up' - resistance really - and are fairly benign. Good for getting away from a sharp corner or hairpin bend.

Most or all Roadster 1.8s and some UK 1.8 versions (Mk 1 & 2), have Torsen LSDs - these work well, but can feel twitchy. Some Roadsters have been retro fitted with clutch type LSDs - these are the full monty, mostly designed for track use, and can feel very rough for road use. You can adjust their characteristics with use of friction modifier in the diff oil. Best avoided for road use. (End of the quote)

You can tell if you've got one if you jack the back end of the car up and turn a wheel by hand. If the opposite wheel turns the same way, it's got an LSD. If it turns the other way, it's open. Sometimes it helps if you hold the propshaft stationary whilst you do this. And it doesn't always work anyway. (1/03)