I also posted this in "drivetrain". Are they the same? I have an '87 IROC. When I jack it up and put it in nuetral and hand turn the right rear tire the left tire also spins forward. I could have sworn the last 305TPI I had with rear disc the other wheel would spin in the opposite direction when I did that. The one thing I noticed with this current car is that when I try to make a U-turn the rear tire on the inside of the turn chirps due to binding. It is similar to my Bronco on dry pavement when in 4X4 mode. All the sources say my L98 350TPI car should have limited slip. But I can tell you the rear tires always turn at the same rate. Maybe someone added a truetrac to limited slip. My question is, Do I have posi or limited slip? Would limited with a truetrac act like posi?
Most cars when turning, the inside wheel has the ability to slow down to help the car turn without pushing the front wheels through a differential. Mine does not. Its not good for handling but its great for launches as I never get the one wheel spin.

 

"Posi" is short for "positrac" which is GM's brand name for a limited slip rear end. The name has been adopted for use when describing any limited slip, sorta like calling a tissue a kleenex.

 

with car jacked up,
1 tire forward other tire backward=1 tire fire
both tires same direction=posi, limited slip, spool, what ever= 2 tire burnouts

 

Oh thanks guys. Thats what I wanted to hear.

 

What's original to a 1987 350 IROC-Z is the 9-bolt Borg Warner rear axle with 3.27 gears, limited-slip & rear disc brakes.

What's curiously interesting is that GM coined the term "posi" yet in the thirdgen years, it is called "limited slip" on the original window sticker.

 

9 bolt uses cone posi,

IMO one of the best posi's around,

when properly shimed it'll light up both in left and right turns,
where clutch packs tend to slip in a right turn

 

Yes it will. I can easily kick out the rear anytime with total control.