g prime

Does anyone know the gear ratios of the GSL-SE rear end(LSD-rear disc) and the non-LSD? Are they different? Do other larger rear end set ups fit in a first gen? Thanks

Rx-7Doctor

iTrader: (13)

Gsle are 4.10, gsl are 3.90, complete rear ends are interchangeable althought the driveshaft
flange is larger in 83. The 3rd members are interchangeable for84-85a ll and 81-83 all. rx7doctor

steve84GS TII

SE is 4.09 but Ive heard it can vary a miniscule amount.The other 84-85 rearends are 3.90 regardless of LSD or open diff.The lower ratio in the SE is to accomodate the higher 5th gear ratio and torquier engine.

gslse_in_vt

1st gen GSLSE LSD is 4.083 (1984) or 4.077 (1985), non-LSD is 3.909. I think some 1st gen drag racers use larger ford rear ends, but I'm not positive. You can find the ratios for all RX-7 transmissions and rear ends here:

http://members.ij.net/mrmazda/tranchrt.txt

Rx-7Doctor

iTrader: (13)

Ok guys you are getting nit picky, here is the exact numbers. 83-84 12a is 3.93, 84-85 se
is 4.076, 85 12a is 3.909, now are you happy, must have a bunch of mechanical engineers here, lol. rx7doctor

gslse_in_vt

Just a mechanical engineer college dropout!

1984se

I agree i've measured 3 SE's and they've measured 3.90.

Not ever over 4

-Ryan

DAVID GRIMES

Not trying to hijack, but on the subject of rear end gearing... If an engine is now 200 bhp, the tranny gears are the same, the rear end gear is 3.909, but the tire diameter is now 3" greater...

What gear ( ring and pinion ) would it take to get back to stock ? Is this a good idea ( to shoot for stock overall RPM's per feet travelled or whatever metric you choose ) ?

Since 4th and 5th seem too "long-legged" for the HP and torque ( it can't do 8000 RPM in 5th, but if it could it would be going 197 MPH ), would it be better to go higher / beyond the stock calculation and go for the max and have a 0-100 car that is quick but not fast ? Or would one spend all his / her time shifting the damned thing ?

All the calcuators I've seen fail to indicate an optimum gear, but one should be able to come close with weight, HP, Torque, tranny gears, tire diameter, etc. Maybe one of those "virtual dyno" computer programs. My damn luck I buy that and it wants to know the drag coefficient of a Mode One Mariah or some ****.

Hpefully, somebody should know. God knows I can't play trial and error with high dollar RX7 ring and pinions.

Blake

I have an Excel spread sheet for working through gearing and tire/wheel sizes and how that affects speed at any combination of RPM and gear. I created it over four years ago and added to it as necessary. It also has a worksheet dedicated to most every combination of ring and pinion gears and the resulting ratio. Strangly, I can't figure out how to get a 4.076 ratio...I can get 4.077 (53/13) and 4.083 (49/12), but it takes a lot of teeth. Anyway, here is the link if you want to download it: RPMSpeed.XLS.ZIP.

Besides the stock ratios, alread discussed, are the 4.444, 4.875 and 5.125 for 1st gens. They were not stock on any models, but developed for racing and available through MazdaSpeed and elsewhere (Mazdatrix, etc). Of these, the 4.875s (aka 4.88s) are my favorite. They really wake up a 1st gen, multiplying the torque we have. First gear becomes an afterthough but, otherwise, the stock transmission feels like a close-ratio box. I have used 4.88s on my old peripheral port 13B and more recently on my stock 12A 1st gen...more smiles per miles. Retail prices are pretty steep but if you do a couple autocrosses a year and, thus, qualify for the Mazdaspeed Team Support Program, the prices are drastically lower...under $300 for 4.88s, last time I checked. I got mine for $100 used.

Pele

iTrader: (28)

There's cheaper places to get those aftermarket ring and pinions.

I believe 4.78 can be found on Kia Sportage.
The 4.44 can be found on a early 80's Mazda 4x4 pickup. Use the FRONT differential...
Additionally 4.30 can be found in 99+ Miatas.

Any ring and pinion that will fit a 94+ Miata will fit the RX-7...

g prime

Thanks for all of the info, I think I got what I needed.

brandon davis

iTrader: (3)

so i can go the yard and find a kia sportage 3rd member and it will fit in my 85 gsl rear end????? are you serious?

Pele

iTrader: (28)

Not sure on the pumpkin, but yes on the ring and pinion.

Rotor13B

I think he means just the ring and pinion gear.