Size of rear axel?? and stock gears???

i want to change to a 3:73 posi what would i need???

What kind of car? Year, trans, engine?

Jim

Sorry lol i ended up making 2 posts by accident... its a 1981 pontiac parisienne 305ci TH350 10bolt rear

A ring and pinion set and a aftermarket posi unit available from several manufacturers.

lol i know that much but whats the size of the rear end like 7.5, 8.5??? so i can order the correct parts... im thinking its a 10bolt 7.5" rear, same as late 70's early 80's camaro?? Its running at 2800RPM on the highway at 60MPH i want to get it down to like 1700-2000RPM at 60MPH, now by upgrading to the 3:73 or 4:11's will that improve my RPMS at 60mph or would they be higher RPM at 60MPH. also it does not have over drive just a plain old TH350 1,2,D... IF not 3:73 or 4:11's witch gears would help me out best?

First you need to know what gears are in there now, no? 2800 at 60 sounds like a pretty high numerical gear, you will need to get down to the very low 3's to see 1700-2000 rpm at 60 depending on tire size. As for the ring gear size, removing the cover and checking it is the only way I know how that car, MrPbody may help out with that issue.