We have used the Miata box in our race cars with great success, and it is not bad for a cheap close ratio box. We have actually found these ratios to be better than the high $$ MazdaSpeed ones for our Buttonwillow track out here – it’s the box we put in our EP car for those races. Bob Neal has also won many races using these ratios in his E/P RX-7. So first things first, you need a 1800 Miata Donor box (94-97?) and a 81-92 Non-Turbo RX-7 for it to go into.
The Miata gear set goes straight into a Non-Tubo RX-7 case (81-92), the only real modification needed is to the Miata input shaft, as shown in the pictures below.
 |
These are the dimensions needed. |
 |
Grind off most of the shaft. |
 |
Use the cutter to do the rest. |
 |
Just about where we want it. |
 |
Polishing the shaft. |
 |
Finished product. |
 |
Comparison showing the changes. |