Found this while cruising the web.(most likely been posted before..but enjoy)

RX-7 Stock Rear Axle Ratios
Year / Model Ratio
79-82 3.909
83-84 12A 3.933
84-85 13B GSLSE 4.076
85 12A 3.909
86-88 5-spd All 4.10
86-88 Automatic 3.909
89-92 Turbo 4.10
89-92 non-turbo, non LSD 4.10
89-90 non-turbo, viscous LSD, "GTUs" only 4.30
93-95 w/manual trans 4.10
93-95 w/automatic trans 3.909

 

I would like to add that S5 coupes that are auto are 3.9 but auto verts are 4.1

 

not RX7 but heres the pickup ratios:

74 Manual - 4.625
74 Auto - 4.375
75 Manual - 4.375
75 Auto - 4.111
76 Manual --4.111 (5-speed)
77 Manual - 3.900 (5-speed)


my old 74 was a total granny shifter

 

4.624, oh my god, lol!

 

I wish we could easily get 4.78's or more .

 

i recall something mentioned about kia ring and pinions fitting in the FB diff, that may possibly be a fit for the n/a rear axle.

 

I have the Kia 4.78 gears in the back of my B2200, really wakes up the 13B, 60MPH in 5th is now 2800RPM. They are short pinion, so nor sure how you will get it to fit the FC.

 

Speedsource used to make 4.88 and the same with ISC racing.

Welcome to Rebello Racing and Mazdatrix can do the fabrication for you.

Rebello costs about $350 + shipping them all the gears to do the modification. I may be doing a spare one here in the future.

They have to graft the pinion gear onto the long shaft.

 

According to Mazdatrix's website, the labor is $1090 to graft the long pinion to the 4.77 ring gear. I don't know if this is just the labor of grafting, or includes re-installation into the housing though.

 

seems like a lot of hassle for an old differential. may as well go with a ford 8.8 and have gear choices.

 

Since this is turning into a Diff gear discussion...What can the TII Diff (say S4) internals be replaced with?

 

the Mazda P type differential is found in the FD, Rx8, and any piston engine v6 or turbo 4.

the FC of course has an oddball long pinion, but other than that all the other stuff interchanges.

the S2000, uses the smaller M type diff, which is shared with the miata, and non turbo rotaries back to the beginning

 

My TII diff has a broken gear in it so I have to ask..what about the FD Torsen as a replacement?

 

Except the S4 88' vert, which are all 3.9

 

the FD and FC cases internally can accept either combination, vice versa. the RX8 should as well, since the 8's gears supposedly fit right into the FD case but i haven't tried it yet. i do have a spare turbo diff and a spare RX8 torsen diff, one of these days i will probably swap out the viscous LSD in that case for the torsen, if i actually keep my car.

which actually sheds some light, now why wouldn't the RX8 4.3's fit into an FC case... hmm. the FD guys have been doing it for some time, since it was stumbled upon.

 

Hence why I said S5

 

The diffs swap from FDs to FCs... but not the gears. The FC has a long nose pinion, so you can't really get gears from anything else.

The service mazdatrix is offering is taking a kia or rx8 gear and extending the pinion so it fits in an FC.

ford 8.8 is the easy button.... I had 5.12s in mine, just swapped them out for 4.56s .

 

Being NA, I think going the 8.8 route is a bit extreme. Even with the 4.3 I have it feels like my gears are far too long.

 

I have in my possession 5.38 gears bolted up to a Torsen unit that fits any first gen. I love it. I wish I had this set when I had my MG with a 13b. It was a pain getting them but they can be gotten.

CK

 

What a tease... spill the beans man, where'd you get such a swap?

 

I spent about 8 months searching the internet for different gears for my race car and I was also looking for a Torsen that would fit a first Gen. I finally got a lead that WPS Racing in Australia might have what I needed. I originally wanted just the Torsen but he also had gears. When I asked him what he had and he said 5.38's I said "sold"! I had never seen 5.38's for a 1st Gen and I knew if I bought the Torsen and gears I would have a unique piece. It's the perfect setup for SCCA Solo 2. I have recently pulled everything out of the car since I am going to a quick change so now it sits on a shelf until I build another car.