What's the difference between these two Torsens?
 

I've compiled two torsens. One I bought from a guy who pulled it from a 90-93 chassis, so i know it wasn't original to the car. Came with single piece axles.

It has this metal tabbed ring on it:
https://www.miataturbo.net/attachmen...ine=1451968866

This torsen I got along with a motor setup i recently acquired. Everything came out of a '96 m edition. I have no way of knowing if it was original to the car or not. It does NOT have the tab ring.

https://www.miataturbo.net/attachmen...ine=1451968866

I can't seem to find any information on if that tab ring makes any difference in Torsen gearing or not. When I search for images of a 3.9 torsen, the ones I see don't have rings. When I search for 4.1 torsen, i see ring tabs. I'm working on getting the torsens opened up but a few of the bolts are giving me headaches. Can anyone chime in? IF i do get them opened, what am I looking for/counting to be able to tell what it is I'm working with?

Thanks

pinion teeth/ring teeth = ratio

Thank you - I'll be sure to take a closer look if i can separate them without rounding the few bolts giving me fits. I've tried heat, PB, screaming, you name it.

As far as the metal ring with the tabs...the "guide" if you will - Any idea why some torsens have it and others don't?

I know it has nothing to do with gear ratio, but nothing else. Don't even know what it is to be honest.

You can turn the thing and count revolutions to get the ratio, doesn't need to be open. However many turns on the pinion to get one rev is the ratio.

Pull the axles out and see if you can see completely through the diff.

Differential Spotters Guide

Oh I know for sure they're both torsens, clear as day through the axle holes.

so as I'm turning the driveshaft flange I'm looking inside the axle hole to see how many turns it takes for the internal teeth to make a full revolution?

Oh I misread that the first one was legit out of an NA6, not a removed swap in an NA6. twist and count.

Im pretty sure its a torsional damper, the metal ring thing that is.

yes

Thanks everyone. If for any reason the ring correlates to different ratios I'll post it

The damper (large metal ring) is on manual transmission cars and a diff without it is from a automatic transmission car. That is unless someone removed it, common on Spec Miata. Mine is gone, they can fail, They separate at the rubber bond.

IIRC, on '99 + cars, autos were 4:10 and manuals 4:30.