If it weren't for money, I would love to try the highest pinion gear there is available ( a 5something ) to see if it would either be:

1) a total throttle response shift as fast as you can 0-100 MPH quick but short-legged blast OR
2) waste TOO much time spending all the time shifting and making me wish I had different tranny gearing.

Does anybody know about the results from a much higher ( than 3.909 or 4.1 ) pinion gear ? Please share.

I'm about to start the rebuild on that 84 GSL rearend I got and if I ever make a ring and pinion change, now would be the time.

 

I run a 4.88 in the racecar. Tops out at about 140. I would like a 4.44 for the street, or the 4.88 with taller tires. The racecar pulls really hard, very torquey feel. Yes you will shift more with that gear, especially on the street.

 

Many moons ago a buddy I grew up with had a Rx3 wagon with a Bridgeport and a 5:1 rear gear. The factory paint was a little faded and it had wood grain down the side of it. Stock 13" steel wheels. Man what a sleeper.

We use to go out and play with all the guys with their mustangs and vettes. That thing would leave the line so hard it would through you back in the seat and would pull like that up until about 70 MPH. By that time we would have left who ever - waaaaay back. They would be so pissed that a piece of crap wagon would leave them like that. After a while people knew about the "Red POS wagon that would not idle".

-billy

 

I have 4.875s (aka 4.88s) in my daily driver. In fact, I just returned from a 2,400 mile round trip to Fontana, CA (Grand Am Cup race) and Las Vegas, NV (SEMA Show) in the car. Apart from the 25% speedo error and the rather high cruising RPM, it's really no big deal. The high gears really wake the car up, making it feel more torquey...25% more torquey, in fact. Yes, I do shift a lot more now but I actually enjoy working the gears. It certainly has given me a lot more opportunities to practice heal and toe downshifts. Fuel economy is down slightly, but not as much as you'd think. If anything, the lower fuel economy can be attributed to an increased willingness to step hard on the throttle coming out of corners...the added pep is addictive. I still get 20+ mpg on the freeway, even cruising at 5,000 rpm in 5th gear (~85mph).

 

That sounds like what I'm after. Wouldn't happen to have a "spare" lying around would you ? Where do I get one of these tall gears without paying the price of a rebuild for just the parts ?

 

BTW, lower gear sets are not necessarily all that expensive. Brand new, the 4.88s are only about $285 through Mazdaspeed (at least they were, last time I checked). I actually bought mine slightly used (<1000 miles) for $100 a few years ago. All in all, I think they are a wonderful investment.

 

Thanks for the info. I'm officially looking !

 

There's junkyard gearsets available...

Front Diff of early/mid 80's 4wd Mazda truck: 4.44:1
1994+5 speed Miata: 4.30:1 (Added bonus of a Torsen that should fit 84/85 RX-7's)
Kia Sportage: 4.88:1

I believe the Honda S2000 also has a Mazda compatible diff in it... Not sure on the gear ratio...

I love it when car manufacturers deligate adn farm out work to one another.

 

i had a 4.88 and loved it till i ate my thrid member up. Now im back to stock LSD. I might do a gear change soon, but who doesnt like going 150?

 

The 5 speed Miata's use a 4.10, the autos get the 4.30. And the TorSen is VERY nice.

 

So you're saying these chunks or ring and pinions will slide into the '84 GSL rearend ? Just like that ?

and Please... what is a torsen ?

 

Er... that's 1994-1997 spec...1999+'s are 4.30:1 on the 5 speed. And they changed from a type 1 torsen to a type 2...

According to the VIN shipped with my junkyard Miata diff, it was a 1999 Manual, some type of special edition, green one... Front end wreck @ 58K miles.

4 and a third turns of the pinion makes one rotation of the ring.


Yep, should go right in, standard Mazda 7 inch ring and short pinion... Kia and Honda outdourced their differentials (And many other parts for the Kia) to Mazda...

And dig this: How Differentials Work

 

With respect to the Miata R&P swaps, you need the 1.8L units, which are 7" like the RX-7...same unit. The ones from the 1.6L Miatas are too small (6.5", IIRC). I'm not familiar with other potential donors.

Torsens are a type of Limited Slip Differential (LSD), which use gears to distribute torque between the wheels. 3rd gens come with torsen diffs, while earlier RX-7s had either clutch-type (the most common) or viscous (Series V 2nd gens only).

 

ive been telling people the more gear the better, but nobody listens!!!
i had 5.13 gears on a stock 12a with headers and nothing could touch me on the street , that is until i ran out of gear, wich happens quick!!

 

For non-turbos, I agree. However, I favor the 4.875s because they are a bit stronger than the 5.125s. Turbo cars, on the other hand, need the load of lower gears to help build boost, so 4.1s or 4.3s are about the practical limit.

 

Exactly !!! If I have to decide between quick and long-legged, it's likely I'll go for quick. A hell of a lot more fun on the street to rule the 0-100 territory.

About the torsen: So it is a replacement for the LSD ?

 

Or do I get the who;e Miata rearend WITH the torsen ?

 

i couldnt agree more!!!
nice to see someone with knowledge on gear selection !!!!!!!!!

gears can make you(on a n/a car) or break you(gears on a turbo car)

 

torsen= lots of small worm gears that break,

mazda lsd rear ends = clutch type almost indestructable!!!!!

unless you put 700 h/p to them , then they break too!!


also , another thing to remember the more gear you put in the rear end, the more stress it puts on the axles and third member, and........ the less stress it puts on the tranny.....

 

Great ! So I keep the soon to be rebuilt '84 LSD rear with the rear disk brakes and look for a 4.88 or 5.13 ring and pinion.

Is it better to find the R&P and hassle with getting it installed or get a chunk from a rebuilder ? I might have a hard time finding somebody around here to install a R&P.

 

im not sure... i have a spare 4.88 gear set for $80.00

a couple of the teeth are chipped but will work fine, let me know if you want them... i would use them but all my cars are turbo............

getting the 3 rd member assembled shouldnt cost more than $100.00,,,, tops

 

I will see if there's any local talent. If so, I'm liable to take you up on that.

Who does that type of work ( in your area anyway ) ?

 

me... free assembly for forum members... you pay shipping , of course.......
i will need a stock lsd core unless you pay for the core........

 

Ah. You do this... You know what you're doing.

Okay.. so there's a spacer on the pinion... it's available in 4 or 5 different thicknesses each varying by a tenth or so of a millimeter...

How do you decide which one you need? Assemble, put paint on the pinion, see where paint hits the ring? Or throw it together, drive on it, and if it makes bad noise, tear it down and retry again?

I think I've asked this a million times, but either I can never get a good answer or nobody answers, or I just ******* forget to check for an answer or what the answer was or something.

 

Super ! I will want you to do this. I'll be glad to provide a core, shipping AND pay you for your time and expertise. Let me get past the Holidays and property taxes

You West coast guys have no idea how hard it is to even SEE another RX-7 in the Southest unless it's bone stock and run down. The Mazda dealership is helpful with parts, but they have zero mechanics that will even think about touching a 1st gen Rex even for non-engine work.