The 4.88 and 5.12 were never in a production model and were sold through Mazdaspeed. They were only made for the early RX7 and other comp vehicles but never for the 2nd gen. Thats why you have to modify them to fit. Options that will fit from cars are a 4.11, 3.9, and a hard to find 4.52. Post on here for a 4.88 if you want a reasonable track gear for the price. Most people started with the 4.88 before we got the 5.12. I sold the last one I had but will see what I can find if you want one.