Winter is here in Northeast Ohio so I am going to begin the long process of restoring and mod'ing my 85 GSL-SE. I am looking to add some torque and fun to the old girl and am trying to decide on some new gear ratios. I have three options and want to know what you would do and why or why not.

1) Change rear diff to 4.44 or 4.88 gears
2) Leave rear diff alone and do the Miata 5 speed gear swap
3) Change the rear diff to 4.44 or 4.88 AND the tranny to Miata 5 speed gears.

What do you think? This will be a weekend fun toy, not a daily driver and I am not planning on drag racing. But I may take her out to road race every now and then.

Engine will remain N/A with a streetport, open exhaust, light steel flywheel and 16" rims.

 

I've tried all of the above combinations on RX-3. Miata 5 speed combined with 4.44 gears are good for both street and freeway driving.

 

Thanks Siraniko! Do you suggest swapping out the stock transmission gears with the miata gears as well? Or just do the 4.44 rear end and call it a day?

 

Im using 5speed miata internals on a FB tranny housing. But you can just swap the ring and pinion to 4.44.

 

The Miata gearset will be taller for 1-2-3 and be slightly shorter for 5th.

I had a chart somewhere around here, but basically Miata gears + 4.78 rearend = the same gear spread you have now 1-4. That is, 1st is about the same and 5th will be about the same as your current 4th.

I'm pretty much a fan of the 4.78 final and FC gearset. I'd like to try Miata gears with FC fifth. I do a lot of highway driving and bridge port engines don't like to spin and cruise, they like to be loaded down, but the 4.78 gears improve handling by reducing the amount of right tire lift.

 

With my 13-b streetport (now a bridge), 4.78 was fun on the street but it was not fun on the freeway as I was out of gear. I switched back to 4.44 since I used the RX-3 as my dd. But the fun ended when I cracked one of the rear housing recently, hitting above 11k rpm on a light to light race against a brand new saleen lol. Coolant is now pouring out of the rear rotor housing..will see which one cracked when I take it apart. Meanwhile, I'm in the process of installing a newly done s5 streetported tii with stock ecu and t04 for now.

 

4.44 is an excellent ratio for the street. You'd need a tall 5th gear to enjoy the 4.88 on the street. The Miata or RWD 626 gearset are phenominal, much less rpm drop during shifts. Do both, it really wakes up the car. Or you can do one at a time, no harm.

While you have the diff out you can tighten it up by adding a thicker disc to the pack.

 

Hate to hi-jack this thread, but I seldom lurk in here and found this interesting. I am faced with rebuilding the trans in my wife's GSL SE. A Miata gearbox swap possible? Or should I just stay with a straight up rebuild? I'm having a tough time finding a kit for the rebuild.

 

Get a 5-speed miata tranny and ask the tranny shop to transfer everything into a FB tranny casing. Input shaft needs to be machined or shortened (see mazdatrix faq) but there is a solution to this which never caused me any headaches. HOWEVER, if I were you I would use an 89-91 FC trans with modded trans mount and shortened remote shifter. Rebuilding a tranny is not cheap.

 

Thanks Sir. I am going to take this offline, please see PM

 

Is it not expensive to do the internal swap over? Or are you guys that have driven it doing it yourself? I've dabbled with tranny internals but didn't think the lay-tinkerer wanted to touch that. Maybe my opinion is skewed because I live in Japan, the land of mods and honey, but if I was ripping the gearbox apart I'd drop in an OS Giken gearset into an FC transmission. Strong, excellent ratios (MUCH better than ANYTHING street based), and you could use a 4.88 and still have a 1st gear worth a damn.

 

I had a shop do the trans internal swap and rebuild it all at the same time. Rebuilding a trans requires special tools that the shade tree mechanic doesn't have. Using mazda internals is much cheaper than OS Giken and I only had so much $$ allocated for the trans. And I'd rather have an Emco transaxle with sequential no-lift shift than a Giken.