What year FB (FD is any gears are shorter...numerically higher) gears can you swap into the FC S4 N/A gearbox? I want some shorter gear ratios (yes I realize the gas mileage reduction, but that's not why you buy a sports car so I really don't worry about it at all, the drive is worth it) all the way around, especially 5th gear. I also remember someone talking about swapping in a Miata 6 speed tranny (or the 5 speed), I'm not too sure on doing that, but it's still an option. Also, is the 4.3 the highest final drive that there is for the RX7 w/out serious modification? Any help is greatly appreciated (especially links to people who already did it/write ups) .

 

Do a search on 5th gear ratios and you should get one of my threads where someone cam up with ratios and year cars they came with. Helped alot.

 

Thanks

 

I swapped an FB tranny into my FC last fall. Put the car in storage for the winter, so I don't have much info to evaluate the difference yet.

You don't have to pull gears off shafts, the center section of the N/A RX-7 tranny family are the same, as is the length from input to output shaft. The differences are in the ratios, bellhousing, extension / shifter housing, and internal refinements (like synchros). The '84-'85 are the best candidates, as the earlier models are weaker and have even shorter gearing.

Here's the ratios:

1984-85 12A/13B 1986 - 1990
1st 3.62 3.48
2nd 2.19 2.00
3rd 1.42 1.36
4th 1 1
5th .807 / .758 .697 (gxl) or .711

Felix Miata has lots of good info here:
http://members.ij.net/mrmazda/interc...html#TRANUSAGE

also check out:http://miata.net/garage/tranny_rebuild.html

And of course read the FSM. The '89 FSM has better pictures & descriptions concerning transmission rebuilding.

Basically, what you'll do is split apart the tranny into the three main sections, then put it back together with the FB center and FC tail & (if desired) bellhousing. You have to swap over the 2nd gen extension housing to get the crossmember mount and shifter turret. Also, swap the 2nd gen speedo drive gear onto the output shaft. The bellhousing swap is optional - but the 12A housing is not vented, while the 13B is (extra heat in the clutch from the bigger motor). Make sure you re-seal ALL the seams between the cases on re-assembly or it will leak. Replace seals & gaskets, too. Use the FC switches (5th gear / neutral) so the plugs match your harness. Oh yeah, when you're re-installing the extension housing onto the center case, leave the switches out - it's easier to mate the pieces without them 'hanging up' on the control rod.

That's all I can think of for now - I'm attaching a spreadsheet comparing the ratios, rpm in gears, etc.

Curtis

 

Hmmm, can't seem to get the file to attach.........

Curtis

 

i had a miata driver mention something about the miata 6speed swap. that would be cool if it will actually work. i'm guessing it might not hold turbo power but sould be fine in a na setup.

 

Yea, I don't have a turbo car (I love me some N/A goodness...although turbo's are great too ) so I'm not worried about killing the tranny that much. Anyone got any links to somebody doing a swap before?