ring and pinion gear info.
 

some thing i barrowed from the Miata guys.

Mazda ring & pinion teeth counts Rear ratios

Pinion-- Ring Gear -- Ratio-- Notes
teeth -- teeth
8---- 41------ 5.125--- Aftermarket
8 ---- 37------ 4.625--- NZ Kia Sportage 4x4
9---- 43------ 4.778--- US Kia Sportage 4x4 front diff
9---- 40------ 4.44--- Truck
10--- 41------ 4.1--- 94-97 Miata and 99+ automatic Miata 1.8L
10--- 43------ 4.3--- 99 Miata stick 1.8L
11--- 40------ 3.636--- 2001+ Australian 6-speed
11--- 43------ 3.909--- Miata 6-speed, RX-7 automatic, 79-83 RX-7 all
legacy:
9---- 37------ 4.11--- 616
10--- 37------ 3.7--- 808/72-75 RX-3
11--- 40------ 3.636--- RWD 626
11--- 41------ 3.727--- 76+ RX-3
12--- 49------ 4.083--- Late 84-85 GSL-SE
13--- 53------ 4.077--- Early 84 GSL-SE
15--- 59------ 3.933--- 84 12a RX-7
13--- 43------ 3.308--- 82-84 B2000/Courier Diesel