im lookin to do like 3:73 or a lil higher to my z but i cant find any taht are garented for the stock rear.. let me add in i dont know what the rear is if its limited slip or posi i dont know how to find out so any help would be greatly apreciated. An how much of a diff would bigger gears do to my stock car soon to have headers an exhaust an such?

 

Your car came with a 7½" 10-bolt.

Count the bolts and make sure that's what's still in it.

There are literally DOZENS of gears available for that rear in that ratio. ANY of them, as long as they're an American-made product EXCEPT FOR Richmond (which is a specific-purpose gear that is not to be run on the street: excellent for STRIP ONLY drag racing, but DEATH on the street) will work fine. Precision, Superior, AA&M (Motive), US Gear/Strange, Dana, are all perfectly fine.

3.73 is too much for a TPI 350 with no mods except exhaust. You'll end up with one of those wonders where you can't even begin to shift it soon enough because it runs out so quick. 3.42 is about as far as you should go.

Limited slip and posi are the same thing just spelled different. Doesn't matter if it has that or not, as far as what gears to get.

What REALLY matters is what gear it has NOW: if it has 2.73 or 3.08, then your carrier is a 2 series, and you'll need either the "special" gears, or a spacer, or to buy a carrier. If it's 3 series, 3.23 or higher, then any "normal" gear higher than 3.23 will work.