OBX, clutch type or Torsen Diff for track use?
 

So I hope someone can chime in and steer me in the right direction (pun intended). After my last lemons race I noticed that there wasn't much in the way of lock-up in my rx7/miata clutch type diff. My buddy held one tire and without too much effort I was able to rotate the other tire using just my hands. Which tells me that the clutches are just about dead. So I'm kind of at a loss for what to do. Car is an 2.4 Ecotec Miata which stops making power at 6200rpm. I should also mention that the car handles great and at one point we lead the race for 30min.

The parts to rebuild the clutch type (with my mazda racer discount) are about $300 which is kinda pricy when compared to others. I also have a torsen that is setup with 4.778 gears that I could move over to a diff with 4.10 gears. Or spend a little more and get an OBX diff for $450. I know that most people don't trust the eBay Chinesium but I just got off the phone with a guy from Advanced Autosport that said they put one in a car without changing the bolts or washers and ran it at Road America in an endurance race without any issues and they liked it more than a Torsen. Maybe their construction has gotten better?

Options:
Rebuild clutch type-$300
OBX-$450
Open diff-$0
Torsen-head ache

I've heard from pretty trusted sources that the 2-way clutch diff from the RX7 is terrible on a road course. I'd go Torsen personally. Especially since you have it already.

Having a decade or so experience bon both OEM Torsen and OS Giken, I hope I can comment. The OBX isn't as good as as well set up Torsen. Yes, Torsens can be rebuilt and "set up". The OSG exists in a category of one. No other clutch type diff on the market for the NA/NB even comes close.

The OSG will produce lower lap times than any Torsen at any power level. The delta between the two grows as you add power. By the time you get to say 300 horsepower there is a vast gulf in performance between the Torsen and the OSG.

Thanks Emilio! Got a lead on a used OSG diff that won’t break my wallet? $1500 is kinda outside of my budget.

Also is there a guid to setting up a torsen or where to buy the parts?

Walter Motorsport for the Torsen setup.
We have a used 3.3 OSG with our Supermiata tune, complete in housing for $1900.
New OSG with our tune is $1450
Email info@949racing.com for more info

You can shim up the clutch type diff for the cost of a couple coke cans. https://forum.miata.net/vb/showthread.php?t=200846

I did a full OEM rebuild on mine and ya the lock up was garbage, it took a few trial and error re-shims before I got it to lock up how I liked and it's been great since.

The RX-7 clutch type is not helping you at all. If you cannot afford the OSG, which is understandable, run a torsen, untouched. Use quality fluid and save your money for other parts.

So do I just cut up a can and make shims from the can sidewall then insert them into the stack up?

Essentially; yes. They are there to press the friction plates together more so they go just inside the conical washer. IIRC I have one coke can shim each side and I was around 90ft/lbs of preload, I've ran 200 which was essentially a welded diff, and 150 which was still too much imo.

The link I posted has some good details in it.

Dean