3.73's or 3.90's ?

I got a 93 z28 (auto) and i need to up my ratios...what is a good company to go with and what ratios should i get 3.73 or 3.90? would anyone no the spline, bolt and diameter i would need? Thanks alot guys

First off, I don't know anyone who makes 3.90 gears. You can get 3.73 or 4.10 ratios for 10 bolts.

You need a set for a 7.5" or 7.625" 10 bolt carrier. They are the same gear, except one is 1/8" bigger. Depending on the carrier series you have now, that determines the series gear set you need. 2 series is a fatter ring gear, and 3 series is thinner. They have 27 spline pinions.

Motive makes the 3.90 for our 10 bolt, Thunder has them.....