for those of you who know me, i have been thinking about putting a miata transmission into my 89 GTU. i know this swap is common on race cars, but i have never heared of it being done on a daily driven car before(i serched, but i may have missed something). my car has a bone stock S5 motor(22k miles, running strong)and a stock exhaust system. i chose the miatabox because the gears are closer.
i picked up the transmission for $125, used from japan in excelent condition. no gears or synchros had to be replaced.
i decided to go with a racingbeat race pressure plate, and a racingbeat aluminium flywheel. i also installed a competition tranny mount at the same time. i am also running NEO synthetic 75w-90 in the new transmission. installation was done by John at Mazdatrix(thank you!)and the transmission was done by Brian Fields(thanks!)located right behind Mazdatrix.
in order to install the miatabox in an FC, the imput shaft has to be modified by a machinist, and the miata gears need to be inserted into an FC case.
the miata transmission has a very tall first gear, and it was assumed that driving the car on the street in stop and go traffic would be tricky. as soon as i drove the car around the block, all my apprehensions dissapeared. it is extreamly easy to drive the car, starts and hills feel about the same as they did with the stock setup. driving the car around town is a blast. it revs up quickly due to the flywheel, and i can ACCELERATE in 5th gear!
i took the car to Streets of Willow on saturday, and it was absoloutly a blast to drive. i have driven on that track before with my stock transmission, and the difference was quite noticable. 2nd and 3rd gear are much closer, and the car feels more spirited, zippy, and responsive than ever before.
top end in 5th gear is somewhat reduced(155mph @7500rpm)but 5th gear feels much stronger and more responsive. i would say it feels sort of like a 4th gear.
i had a Mazdatrix short shifter installed on my stock tranny, and it was quiet as a mouse. after we installed it on the new tranny, it rattles like a ****, which has lead us to conclude that shifter rattle is specific to each transmission. more on this topic can be found on the Mazdatrix website.
everyone who has driven the car has given me positive feedback, and the car is an absoloute BLAST to drive. the results completly exceeded my expectations. in my opinion, there is absoloutly no downside to this swap. i would definatly reccomend this swap to almost anyone with an FC. the transmission has completly woken up my motor.

 

Have you compared MPG before and AFTER yet? I'd say thats probably the downside.

 

crusing on the freeway at 3500rpm(best gas milage in my car)is about 80mph. so far i would say that the gas milage is not noticably different. when i drove up to willow, i used up 1/4 of a tank, the same i used when i drove up on the stock box.

 

What's was the final cost?

Sounds great.

 

very cool you should do a write up with pictures I might want to do this

 

im hoping to upload some pix soon, my home computer is being a bit screwy though.

 

wow that sounds awesome man... i would also like to see some pics and whatnot...

 

cost would vary from person to person, depending on what needs to be replaced(to bearing, clutch fork, synchro, etc) but cost of the major components are as follows:

tranny: 125
aluminium flywheel: 455
race pressure plate: 140
stock clutch disc: 71.33
tranny mount yblock: 23.91x2
tranny mount saddle: 72.32

labor will vary depending on what is being done to the transmission(replacing synchros, etc)and on the install(new clutch, if you do lsd or something else in that area, etc)
for those who have not yet replaced their driveshaft, during this swap would be a good time, as the stock driveshafts tend to lock up(i would know!!)and i find its always a good idea to start with fresh parts

 

Wow, I've heard of this swap going the other way (FC int a Miata) but not this way around.

Are you making a 1/4 mile racer or something?

 

She's not a quarter mile person...If I'm not mistaken, she's more into the autox style of driving, maybe a little drifting here and there.

 

which clutch/flywheel are you using? the miata ones or the rx7 ones?

rx7 ones right.

 

the tall 1st gear would make for a TERRIBLE dragbox. its a great road race box, due to the shorter gear ratios. i havent tried drifting on it yet, but i believe it would be good for that as well.

yeah, the rx-7 ones. we put the miata gears into the FC case, allowing us to use the stock bellhousing and driveshaft.

 

ywea this owuld be great for me to swap out for autox

 

That's better gearing than my GTUs, that bitch sits at 4k rpm at 80.

 

mmm gtus has the 4.3. eventually id love to get a 4.3, that would REALLY put some spirit into the car!
the gearing really is great...i have a chart showing the gearing for both the stock box and the miatabox with my stock motor...ive been trying to scan it in at home, but my scanner isnt working right.

 

Wait a second... you topped out 5th gear at 155mph in an NA FC?!

 

nice, that sounds awesome.

 

I drove her car a few times after the tranny swap, like she said its spirited and fun to drive, I liked it

 

no, that is how much 5th is good for @7500rpm with this tranny. i did hit 100mph in 3rd though

 

You're making me want to do this swap rxgirl...I just gotta get the right motor before I start wanting tranny mods...plus with me wanting to build mine more for drag than drift/autox, I don't think it'd be too good for me...but the 4.30 gears, that sounds good to me

 

I love this girl!

 

So basically you used the internals of a miata tranny and placed them into an fc tranny case?..So its all bolt in i assume. Also anyone know how much tq the miata tranny is rated for?

 

...in that lies the problem, the miata transmission is about as weak as the n/a FC gearbox; you may get some awesome gearing out of it but you wouldnt want to start laying down power with it.

 

The Miata tranny is reasonable resilliant. They can take 300hp+ to the wheels if you don't launch on drag slicks. I wonder if you can use the stock RX-7 first to get a better launch and better autocross performance. That would be good. I know I often complain of the high gearing at autocross and for highway performance in 5th, but it helps with milage. I know Miata tranny's can take RX-7 5th gears, so you could probably keep it to get the same sort of fuel ecomomy, and have the stock 1st for better launches, but then you may end up with some strange gear spacing.

What's required of the input shaft machinig?

 

oh yeah nice Swap, get yourself a 4.3 and see what you top out at!!!