Hey guys, I have just finnished swapping out my old 2.8 mpfi & 700R4 in my 89 firebird for a custom built 355 & rebuilt th350 with a 3000 stall converter. The rear end is a stock non-posi, 7.5 inch 10 bolt, and my question is thus. What gears do you think I have? I always believed that I had crappy 273 gears, but when I had the car on the highway for the first time I was doing 3000 rpm and going about 60 mph!!! I wanted to swap out the gears for a set of 342's or 373's but if I all ready have a good set of gears, then I only need to get a posi for it and not the full set.

 

pull the cover and look

 

I knew I could do that, I just wanted to save some time & effort if someone could knew what I would have.

 

according to the tech data page here on TGO, it says they were 3.42's if they are the original gears.

https://www.thirdgen.org/newdesign/tech/techdb.shtml

 

Still best to pull the cover and look. My car should have came with 2.73 gears going by that chart but when I pulled the cover, it had 3.08 gears.