Torsen questions
 

I've got an open rear in my '02, so it obviously needs a limited slip. I have a lead on a used RX7 clutch type for just over $400, but what I've read here makes me think the torsen would be better for autocross and street driving at ~250whp.

Any suggestions on where to look for a used torsen unit? Planet-miata doesn't have one right now, the classifieds haven't listed one without the whole assembly for as long as I've been looking, Partsgroup is closed until Tuesday, and Ebay only has ones shipped from Japan.

Also, will the internal torsen unit from an MSM just bolt into my open diff? I know the whole swap requires the axles, but I can't find anything about just the LSD.

Oh, and one last thought I just had: Would it be easier and no more expensive to just do the whole swap and sell my open diff afterward?

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Swapping the entire pumpkin and axles would be easier. If you get into just the LSD unit itself, you'll need to have a driveline shop/specialist assemble and set the backlash...which is more cost and downtime. This is worthwhile if you're adding an aftermarket LSD such as a Cusco,OSG,Quaife etc...

There is also Mazmart, Panic Motorsports, Parts Group and numerous single-person dismantling operations.

The MSM unit will require MSM axles as they are bigger and have more splines.

Be aware of the different R&P from year to year as well as you can get a TorSen with a 4.1, 4.3 or a 3.9.

The RX-7 LSD is an OK upgrade, but getting the preload can be a PITA..they like to go high or low, the sweet spot is hard to get. There are TONS of threads on m.net about this. IIRC FatherLeadfoot has a good comparison/review of the RX-7 CLSD and the different preloads and how it acts. $400 for one sounds kinda high.
http://forum.miata.net/vb/showthread.php?t=308131&

Ok, well I guess I'll start looking for a whole pumpkin instead of just the torsen. How much should I pay for one of those?

http://atlanta.craigslist.org/nat/pts/2184707973.html

This guy is one of our locals, he parts Miatas for a living and is a very good guy. Don't know if he still has all of these or not, but it's a good start and the prices are fair. (I'd stay away frrom the 3.9 T-F diff as well.)