ok so im thinking of buying one

but idk anything about cars

what the hell is a 12-bolt posi 4:11

and whats its purpose

sorry if it sounds idiotic

but i want to know

they are selling a 1970 pontiac tempest for $5000

the description is as follows:
1970 PONTIAC TEMPEST 350/350, 12-bolt posi, 4:11, alum radiator, much more, 13 sec drag

but im not sure yet

anyone please let me know what you think

A '70 Tempest is an "A" body, same as Chevelle, Skylark and F-85 (Cutlass). The 350/350 would indicate a Pontiac (NOT a Chevy) 350 engine and M-38 (TH-350) transmission.

A "12 bolt posi" is a Chevy rear axle, with PosiTraction (Chevy's name for a limited-slip differential). "4.11" is the final drive ratio (engine turns 4.11 revolutions for each revolution of the driveshaft in "high" gear). There were a number of rear axles installed in Olds and Pontiacs with 12 bolts holding the cover on, but only 10 holding the ring gear to the carrier (the REAL reason they're called 10 or 12 bolt). Pontiac called their limited-slip diff "Safety Trac".

Lots of goodies for the A-body. Virtually every part that fits GTO fits Tempest. If you're looking to build something with serious power, get Jim Hand's "How to Build Max-performance Pontiac V8s" published by SA Designs. It's a current study of the old Injun ("traditional" Pontiac V8). The Pontiac V8 is among the best of the street performance engines. No need for a Chevy here! That 4.11 gear is WAY to "steep" for the Pontiac.

Jim