What posi-trac rear end would be ideal on 92 firebrid

Your car came with the 7.75 inch axle and was available with 2:77, 3.27 gears. The earlier ('87-'90) 3.45 will also bolt in. Be careful in that the available stock 3:45 gears will only fit the 7.625" axles. Auburn or Yukon posi is the best deal going, easy bolt in, and available in lots of ratios. You'll need to make a few decisions before selecting the ratio: 4 speed, 5 speed, manual, auto trans? How are you driving the car - mild street race, or all out, or a little of both? If you want decent gas mileage and wicked performance, you'll want some kind of overdrive trans, and that's going to determine the rear gear ratio. My point is, you can go with a stiff set of posi gears if you have overdrive, otherwise I would not go past the 3.27 with your engine. Good luck, the 92 is a great platform.