bschnard

iTrader: (4)

Has anyone put a late model Miata rear end into a Non-turbo 2nd gen? I am exploring ideas on how to get better selection of gears for the rear end for autox. Running an 87 NA 5 speed. I suspect at minimum some custom fabrication for suspension and customer driveshaft. This would be my first attempt at something this major and unique so looking for suggestions and even criticism so feel free to tell me how crazy I might be.

Thanks in advance.

Spectator

iTrader: (1)

Why would you want to do that?

Roen

iTrader: (2)

Torsen LSD into an N/A 7 inch rear diff

If you want custom rear end gears, look up ISC Racing. I think they had 4.88 and 5.12 rear gears for the 7 inch diff.

bschnard

iTrader: (4)

I have sent them an email to see if they still offer that but was also exploring other options because I had heard they might not be able to provide the long pinion. I am keeping my fingers crossed that ISC comes through for me. I have a good local Mazda specialist who will setup and install a LSD for me once I come up with gears and they thought about asking about the Miata swap if I can't find gears anyplace.

Roen

iTrader: (2)

Mazdatrix has 4.3 gears

matthewromeril

i have the later rx7 turbo but wen i looked into this i found that swapping from a 4.1 to a 4.3 diff ratio would give a 7% reduction but i also looked at wheel size i dropped from a 205 55 16 to a 205 50 15. (convertable wheels) but stock 15 often come with 60 profiles this was an 8 percent difference. the 2 combined is a 15%. but if you want onle a small drop the tyres are a cheep way to do it. I think they made some early fc's came with 14" wheels but wont fit with 4 pots.

bschnard

iTrader: (4)

Thanks for the info, I have the 4 pots so 15's would be as small as I can go. My ultimate goal is to get enough change so that I can stay in 2nd once I get there and keep my revs high enough to stay within the power range and not bog down coming out of the corners. I wanted to try for the 4.88's first and then had already considered your option with the LSD and smaller wheels as my backup plan.

Then if plan B is still not enough maybe swap in a Miata tranny since it looks like 2nd gear might give me a little more help in that area. I am looking in several areas at the same time so not limiting myself to any reasonable options.

Of course right now the guts of the engine are stock so a rebuild when it comes due will include most likely an agressive street port job since that is legal for Prepared class.

We are also still working on improving the drivers rather than just the car and I know I have a lot of room to improve in that area. But I still have lots of fun working at it.

zilch321

I was fairly certain as i've searched around this site that there were some write ups with photos on someone swapping a Torsen LDS into their RX7 here. They had to reuse some existing ring from the old rear to make it work correctly? This is fuzzy but I know there is info about this somewhere in here.

Sideways7

iTrader: (7)

You can swap the miate torsen diff into the NA rx-7 casing. You have to use the rx-7 ring gear and case to bolt up correctly, but the actually LSD itself is a direct swap. There is a writeup in the archives.

bschnard

iTrader: (4)

Yes, I saw that writeup but that goes back to my original problem, needing the long pinion with the long shaft which means very, very limited selection of ratio's.

Shainiac

iTrader: (7)

According to Grassroots Motorsports magazine, Mazda used the 7" RX7 ring and pinion on the torsens on '94+ Miatas. I believe it was even the 4.10 gearing. IIRC, the writeup in the archive switched back to the stock ring gear because he wanted to retain the GTUs 4.3 gearing. Ive never seen anyone do a direct drop in without changing the gear but it would make sense.

Sideways7

iTrader: (7)

If you want to to use everything from the miata, I would think it would require custom mounts, custom driveshafts, and custom axles. It just seems like a whole lot of trouble for s slightly better selection of rear end gears.

Black91n/a

You can re-use your stock rear housing, they're the same in the Miata, but they use different mounts. You'll need to fab something for a front diff mount and you'll need a custom driveshaft that's longer and has the Miata bolt pattern on it. You can use your stock stubs and stock axles.

It shouldn't be too terribly difficult, and considering the cost of getting someone to do the custom work on the pinion, it might actually be an economically competetive option, especially if you do more than one ratio. Keep an eye on the classifieds though, a 5.12 or 4.88 comes up every once and a while.