There was a posting showing the model year Miata LSD that can be swap into 84/85 RX7. Post had detailed pics showing step by step process; including how much of the Miata LSD housing had to be trim to install into RX7 rear axle (allowed clearance for Watts). Does anyone have link to this old post? Been looking for it in thread search, but can not locate.

 

i kind of remember the one you're talking about.

the 94-97 is a 4.10 Torsen
99-02 5 speed is a 4.3 Torsen
99-02 6 speed is a 3.9 Torsen
03-04 is the same ratios, but its some spring loaded thing and not a torsen anymore

 

I think this will cover any and all questions you have about the LSD interchange between an NA Miata and a FB Rx7 (written from the perspective of taking an Rx7 center section and adding it to the Miata). Adding the archived rebuild thread as well since you'll most likely need that reference doc.

If you have questions about where I got that info and I didn't reference it in the docs, I can find them again. If you are looking to use the Torsen diff from a Miata (94+) it has to be a big bearing rear. Question is why? They are effectively an open diff past the torque ratio. Good for normal day to day driving, but not advantageous over the clutch pack LSD if you want something closer to a spool.

 

Miata diff and the area you need to remove to use the watts.


Miata center section mounted in a 1st Gen RX7 rear, after the surgery shown in my 1st pic. (this diff is upside down in pic).

 

Perfect - was exactly the information I was looking for.

 

You can also just swap the differential, keeping everything else RX-7. This is what I did, and it's a nice upgrade. I think Torsens are the right answer for performance street driving.

 

Now that I think about it, that rubber flexdisc isn't designed to withstand all the angular travel you'll see with a live axle. Have you driven the car yet?

 

It's not my car. I was looking at doing this mod about a year ago and gathered all these pics, for my own reference. I pulled them out to show the OP what it looks like (since I already had the pics).

 

👍🔝I am also just swap the miata 26 splin torsen 2 in my Rx7fb and it feels like driving the new Mazda MX-5 4 (ND) RF 2.0. The diff is so quiet and "drifty"😉

 

that isn't what it is, its just a damper, the miata still uses normal U joints like the Rx7

 

Thanks for clarifying.