transmission gear selection questions

[Rogue_Wulff]

Originally Posted by Low Impedance

as for the miata transmission here is what i found

Ratios:
1st 3.136
2nd 1.888
3rd 1.330
4th 1.000
5th 0.814
Final Drive 4.300

That is basically a split between the stock rx7 and the mazda comp transmission. I think i need to go talk to some people who have been racing with these ratios and get some advice.

Mostly true, however most 5spd Miata's were equiped with a 4.10 rear gear.
The 4.30 or 4.10 Miata ring and pinion is a direct fit for the FB rearend, as the FB and auto trans Miata shared the same 3.90 R&P.
The Miata trans internals can be swapped into a N/A RX7 trans case by simply milling ~3/8" off the front of the splines on the input shaft.

Using a 4.78 or 4.88 R&P really requires the hardened driveshaft front yoke/ roller bearing tailshaft mod. The driveshaft will reach RPM's too high for the stock yoke and tailshaft bushing to be properly lubed, and failure will only be a matter of time.

There really isn't any set "Perfect" trans/rear gear ratio setup, it all depends on how/where the car will be used. What works great at one track, may suck badly at another track.