rear diff advice

my firebird has an 8.2 rear diff. Im opting to replace it with a 8.5  and during install id like to throw a posi unit in with it also. My question is ,would a factory posi unit perform just as well as a eaton aftermarket unit; and if the factory unit could be built to perform with todays posi locking units if it didnt?  

There are variables to consider, how much torque the engine puts out will dictate the type of rearend. Also, switching to 8.5 will require changing the entire rearend assembly. 8.5 carrier is to big for the 8.2. Eaton limited slips are stronger than factory limited slips, they are also rebuildable. Powertrax makes lockers(stronger)for both 8.5 and 8.2. Check Jeg's.com for pricing. Hope this helps, Tom  

Eaton is a good poi, but you would be surprised how strong a factory one is. Before my latest upgrade I ran a 455 in a 3800lb TA. Even at a high alt, the car ran 11.9's on motor and mid 10's on Nos. Over 12 years I ran 30,000 miles on a posi that already had 80,000 on it and put over 2000 passes on it. I even punished it was a high shot of Nos once, running 9.80 with a 60 foot of 1.51. Not bat for 3800 lbs.

The posi is not where people blow out the rear. The problems are always from the gears pushing and tearing the diff out the back. New clutches are $20 and easy to install.

If you are going to run more then 400 HP, then you need to have the axle tubes completely welded to the center section all the way around. Make sure you have this done by a professional who will put it into a jig to keep it straight and will also heat the tubes with a torch first.

If more then 550hp, then install an Alum diff girdle in place of the rear cover. This will keep the caps from moving out. With this done, I have seen many cars run 9's at the track with  factory GM and aftermarket 8.5 posi.  

You could always just find a donor 73+ Nova.  Those are a direct fit for a First Gen bird if that is what you are looking for.  If it is a 2nd gen, then there should be literally thousands of posi units with the 8.5 from other 2nd gen Birds.  I have an Eaton in mine and am loving life.

AK