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Hey gang, So, my Miata donor has provided nearly everything I'll need for running gear. However, one thing it doesn't have is an LSD.

How important is a limited slip diff?
-What will I be missing out on if I stay with the open differential I have?
-Is having an open differential desirable at all?
-Does a Seven even work at all with an open diff?

If it is critical to get an LSD, which do I get?
-Do I source a Miata LSD?
-Do I need to find a Torsen differential, or is a viscous LSD satisfactory?
-Are there betterl lighter, stronger LSDs than the Miata I should consider sourcing before starting the build?

Thanks for the enlightenment!

How important is a limited slip diff?depends on your use
-What will I be missing out on if I stay with the open differential I have?again, depends on your use
-Is having an open differential desirable at all?not really but for inital shakedowns you won't mind at all.
-Does a Seven even work at all with an open diff?yes, remember the miata had an open too

If it is critical to get an LSD, which do I get?personally i recommend a torsen type unit
-Do I source a Miata LSD?sure why not?
-Do I need to find a Torsen differential, or is a viscous LSD satisfactory?again, depends on use, i use a viscous when building for smooth transitions and calm driving styles but prefer the torsen type for performance vehicles
-Are there better, lighter, stronger LSDs than the Miata I should consider sourcing before starting the build?you can always make small changes mid build, driveshaft and axle attachments to the diff are just as if not more important than a lot of other considerations. "better" is subjective in a lot of things. ..

Limited slip
Good for high horsepower situations,
Good for driving away on ice or wet roads in a straight line
Good for going crosswise and throwing your car in a ditch on icy or wet roads
Good for putting your car sideways in a curve under power and doing a 360
Good for breaking an axle when it locks from side to side, assuming your axle is weak and your engine is strong
Great entertainment for your friends assuming you have enough power to fishtail



Open diff
Good for burning one tire off while in a curve
Good for a smoke show to impress your friends
Good for hauiling butt around a curve assuming your tire has traction

A little tongue in cheek, but to be honest these are fun cars and a LSD is strictly up to you, even the early Shelby Mustangs didn't come with an lsd as standard equipment, each has its limitiations, though in the end an open diff is safer to drive in most conditions.
Personally I would think the average Miata doesn't have the power to really warrant it unless you are really serious about racing it.

In my build I happen to have a limited slip, not because I went looking for one, but because the cheapo rear end I found happened to have one.

I would say run it as is, if the need arises later then look for one. You would also probably get a better price if you are not in a hurry in your search.
Al

If you aren't going to be die hard racing I'd just use whatever LSD you find. You can always change to a different type once you have the car on the road.

Some of the comments about LSD causing problems in the rain have me perplexed. As an example, I purposely floored my XKE in low gear when going around a 90° street corner as I went through a water puddle to see what it's LSD would do. The result was very uneventful other than the car taking off around the corner very fast with neither tire spinning. With LSD you have -more- control because both tires are getting power.

Some limited slips have more bias than others. For instance, a Detroit Locker can be a real bitch in the rain and painfully noisy when backing up or in tight corners as the dogs engage/disengage. I prefer clutch style (positraction, Auburn, Trac-loc) diffs in a street car.

One thing you do not want is a spool!

olrowdy with limited slip on any slippery surface it can get hairy due to the fact that both tires let loose suddenly. When you don't have an LSD one tire stays planted.

I realize a kart is a different beast but the solid rear axle is the ultimate in locker, but in many cars the LSD causes push so how does that kart handle that? Anyone gone from the one wheel drive to solid axle and can tell us?

A friend of mine put the LSD in an Elise, against Lotus' advise, and became just enough slower to keep him out of the points hunt. He went back to the open diff and jumped right back into the fray at or near the top.

What's your budget and what are your goals? Is your Miata a 1.6L or 1.8 L open diff?

If your goals are Low- Cost over outright performance, you can always build the car with the stock open diff and upgrade to a Miata LSD as desired at a later date. If yours is a 1.6L donor you can upgrade to a viscous rather cheaply, as the smaller 1.6L diffs in general are not very highly regarded in the heavier Miata world. This would certainly be the Low-Cost option to get improved performance, and should still be plenty durable in a lightweight Locost application. For the 'ultimate' setup, going to the Torsen diff out of a 1.8L Miata is also very feasible. Miata people have been doing this for years, although it will cost a bit more money as you will need to source the more desirable/expensive differential unit, as well as the matching axles and driveshaft. If it's already a 1.8L open diff car there probably isn't much to be saved in buying the parts to convert to a 1.6L viscous diff, so just go with a factory torsen or add one of the available aftermarket LSD. Overall there really aren't many reasons to go with any heavier duty of a differential than the Miata 1.8L Torsen when using any Miata drivetrain and running gear.

the torsen weights more than the Mazda comp clutch type

Don't assume there'll always be an LSD available of you change your mind later. For some axles there simply aren't any, so check first!

Regarding rain, an LSD can make a huge difference, depending on type and power level. Because it's a limited-slip, that means that on a tight turn, the inside tire is being forced (to some degree) to spin faster than it wants, which happens fairly easily in wet conditions. That means the car's already lost traction due to the inside tire having lost its grip, and we haven't even considered lateral load tranfer. I've had several cars with clutch-type LSDs and they were a real handful in the wet.

When I first got my Locost on the road (2006), it had an open diff. I used a Corolla GT-S axle (the LSD was not available in Canadian Corollas). While I drove it a lot to work, I autocrossed the car regularly as well. I fought oversteer which I tried to tame with front sway bar and chassis rake, but it just wasn't quite "right."

In 2007 I found, rebuilt and installed a factory OEM Corolla GT-S clutch-type limited slip.

The addition of the LSD transformed the car, to the point that I would highly recommend an LSD even if you never race it. It is much more composed on the street, and much more controllable in autocross.

There is a bit of chatter on tight turns if the road is dirty at all.

The OEM LSD is pretty tame, and I think it's perfect for the weight of the car. I figure if I pop the diff (they aren't that strong), then I would find a used TRD unit. I would avoid the KAAZ or CUSCO because in a car this light, the car would likely go straight or sideways and not be as much fun. OBX has (had?) a torsen style lsd that I might try at some point, if it doesn't burst into flames from sheer low build quality.

For a 7, I would recommend a torsen style diff, or a soft clutch type. Avoid the locker style unless you like drifting.

I have autocrossed a 1999 Miata with an open diff and then with the torsen installed.
The torsen made a huge difference. I'm building my car with the torsen without question.

OK, but what rear end were the faster guys running?

Wet street aside. I feel that an LSD is a requirement for any serious sports car. What's the point of building something and just spinning the inside tire in a turn. Adding an LSD to my cars has been (next to tires) the single biggest improvement in performance. The more twisty the course the more it helps. On the other hand, if you're just building a street car, don't bother.

Explain the fact that the Lotus Elise gets slower with the addition of a LSD then? That's a serious sports car and it does better without one, even the Lotus engineers agree.

And Ol'rowdy I have no idea what you are talking about in your anti open diff scenario above. Carguy makes excellent points about why an open diff is safer for the average driver. You might want to better explain that "situation" you describe where you loose forward mo and both tires break loose because of the open diff. I've never heard of or experienced anything like that. IMHO The more likely scenario with an LSD is that you are mid turn and momentarily break traction with the rear from a wet spot, gravel, poor throttle modulation or what not and BAM!- you're now sideways. With an open diff, only one tire breaks loose, usually the inside one (in a turn) which leaves the outside tire with no forces to deal with other than control of lateral roadholding. (which increases cornering stability) I've driven and abused vehicles of both types and I've never experienced what you describe. The open diff to me acts like a "governor" that doesn't let you put enough power down to step the rear out unless you are already at the limit of traction, in which case a LSD would've had you sideways long ago.

What I have found in a nutshell is that a LSD will cause a bit more understeer on track, (hurts on corner entry and helps on corner exit) will make it more likely for you to spin your car out and loose control when you don't want to, and will enable you to spin it out in a semi controlled manner and drift it when you do. Not to mention it helps on slick roads and what not, but who drives their 7s in these conditions anyway. (besides Jack and G ) An open diff really isn't a curse and a LSD isn't a necessity. My advice is build it with what you got and if you get adventurous later then go ahead and install an LSD.

Explain the fact to Elise owners found that they do indeed need one for autocross events, where load-transfer is high. For more straight-ahead driving, it's not needed as much - it's all by degree.