I'm trying to make sure I have the right rear end kit here. I have a 86 Pontiac firebird s/e with a 305 LG4 engine in it. Drivetrain.com wanted to know if I had a 7.5 or a 8.8 rear end. I told them it should be a 7.5. Was I correct on that guys? It's only the low powered 150 hp v8.

 

There's no 8.8 from GM. So you can be pretty sure it isn't that.

The 7.5" / 7.625" (same thing, all parts interchange) was the most common rear in these cars, used in all of them other than 85 - 89 Trans Am and 87 (I think) - 89 IROC. It has 10 bolts holding the rear end cover on, and therefore is commonly known as a "10-bolt".

The Borg-Warner rear with a 7.75" ring gear was used in the other applications referred to above that didn't get the 10-bolt. It's called the "9-bolt" for the same reason the "10-bolt" is called that. I'll let you figure out what that might mean in your situation.

Count the bolts on your rear end's (your CAR'S rear end's) cover. Go from there.