2.76,2.94,3.21,3.23.3.55,3.91 depends on what was orderd when new

most have a 2.76 open diff

3.55 are good for the street

3.91 are better but can get old on the highway

pull the rear cover and change the oil,probly needs it anyways..while its draining turn it to see the yr and gear ratio stamped on the ring gear

few bucks for 2 bottles of gear oil,that info is cheap and will be needed down the road with upgrades...also will know if its open or a sg unit

a short dur cam with high lift works great in a teen for street duty..gears multiply the torque and HP so the lower the better for launching it from stand still