Miata Input Shaft Modification


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.

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