Spec Miata Transmission/Final Drive
a. Transmission and final drive ratios must remain stock for the year of car. 1999-up cars shall only use the 5 speed transmission and the 4.3 differential ratio. All cars may use the stock br /> unmodified OEM open differential or one of the approved alternates listed below.
b. 1990 to 1993 Miatas may use the stock, unmodified viscous limited slip differential or the MAZDASPEED Motorsports Development limited slip differential, part number #QN10-64A00 (previously TOY1-27-200 & 0000-02- 5501).
c. 1994 and newer cars may use the stock Torsen limited slip differential.
d. The 90-93 Miatas may convert to the 99-05 differential housing and the 4.3 differential gear ratio from the 99-05 model years. This conversion includes the driveshaft and half-shafts. The original 90-93 model rear suspension uprights must be retained.