Torsen Compatabilty
 

Ive been all over the web reading about which torsen diff's will fit in different models. (and yes a searched the forum :D ). This is what i found out:
The 7" 94-97 miata torsen will fit in the 84-85 GSL, the fc torsen will fit in the miata.
My question is, shouldnt the fc torsen be able to fit in the 84-85 GSL rearend? Also has anyone on this forum actually performed the swap? Everything i've read just says that it should fit. I know this has been asked before, but i cant find an answer.



http://members.aol.com/solomiata2/RX7LSD.pdf

http://members.aol.com/solomiata/MiataVLSD.html

http://www.jimrothe.com/mazda/torsen.html

http://www.nellump.net/peri/epi/firs...torsenLSD.html

Well, it looks like you missed one major issue though in all your research. The FC doesn't *have* a Torsen.

sorry, what i meant was, a torsen FOR a FC.

i.e. http://cgi.ebay.com/ebaymotors/ws/eB...category=33731

Oh. Well, that one in specific won't fit; you'll note they say it's for the Turbo FCs, which have a larger ring gear and aren't compatible with the FB rear.

heh, i just relized that. i found another auction for something similar and described a 8" ring gear. Thanks though. Do you know if any of the FC's used a 7" ring gear, like the fb and 94 miata?

Yup, the NA FCs have the 7" ring gear.

The non turbo FC, '84-85 FB, and '94-up Miata differentials are interchangeable. ('79-85 RX-7 and '94-up Miata gearsets are interchangeable also)

My question is, why would anyone want a Torsen. :) They're just open diffs that rely on internal friction for their little bit of limited slip action.

You realize that you can say the exact same thing about a clutch-type LSD and it would actually be more accurate? :D Torsens work by a particular way that worm gears bind under load; yes, they act as an open differential as long as nothing's slipping, but when stuff starts slipping they lock up.

From looking at things, it would seem that they work pretty well; WRC seems to be getting away from them slightly in favor of electronicially biasing diffs, but a hell of a lot of lesser people are using them whenever possible; Quaife ATB being one major notable example.

Not saying it's perfect, but they work pretty well from all accounts.

I LOVE the way the TorSen feels in my Miata. Sure it aint the best for drag racing, but in the twisties, where it really counts, it works great....

They aren't used in rally because of their main failing: They can only transmit a torque *bias*. Meaning, if one tire is starting to spin and is using, say, 50lb-ft of torque, then the other tire can only transmit the bias of that, if it has a 2:1 bias ratio (typical of Quaife) then it can only transmit 100lb/ft of torque to the wheel with traction.

If one tire has zero traction, it can transmit zero torque, so the other wheel gets a 2:1 ratio of zero torque, which is, umm... zero! It just acts like an open diff.

Quaifes may have a lifetime warranty but they do wear out under heavy use. Just picture driving hard over a bumpy road, or getting the inside tire airborne over a curb or a yump in the road. I'd rather have a clutch type diff if I had to have a limited slip diff. A tight clutch pack diff is like a spool - you know how it's gonna react. Except that unlike a spool, you can make tight corners without hurting the driveline.

Well, in theory anyway. My LSD is too tight even for low speed parking. It's a riot.

That’s all great and dandy peejay. The bottom line is that 99% of the time, bump and curb hitting aside, a torsen will feel better, require less maintenance, and will probably be faster around corners. I have yet to see my torsen spin only one wheel.

How much less maintenance than zero can a diff have? :) At least, my low mileage car (only 158,000 miles) has a tight factory LSD and the rearend looks like it was never off or opened.

I see where you're coming from... you're from CA, so you're probably used to glass-smooth roads. :)

true, the roads here are pretty nice. :)
as far as maintenance goes...I've seen some last as long as yours, but others not even close. A good torsen will never wear out.

whcih miatas have torsen, and whatre miata rearend ratios over the years?

anyone know where If cusco or kaaz make 2way or 1.5 way lsd for the 1st gen

First, TorSens are NOT 'open difs with a bit of limited slip' They're zero slip. They send the torque to the wheel with the most traction through a series of mechanical worm gears. They can send ALL the torque to a single wheel when neccessary, as in the Canadian Forces Iltis vehicles with the Audi drivetrain I worked on for 6 years - we joked about it being 1 wheel drive.

Second, Audi kicked major ass with TorSen diffs in their Quattro Coupés in the 80s.

All C Package Miatas have TorSen diffs(tan top, tan leather interior) It was an option on B package cars.

5 speed Miatas got a 4.10 final drive, the autos got a 4.30...

Same here. Anybody know this? It'd be cheaper than a Ford 8.8 conversion.

I dont know where to find one. but any 7" gear for a miata or NA FC should fit. Check ebay, they pop up there pretty often. Or maybe the rx7store.net.

DF, from what i gather, the torsens dont take abuse as well as viscous LSDs. The only one that might take the kinda power your putting down on a regular basis would be the guru unit. There products seem to be built very strong. But like i said. I have no hands on experience with this yet. (funds limited)