hello
my car is an 87 z28 with mainly bolt ons mostly edelbrock, anyway im guessing that the guy who i bought the car from changed out the gears in it, the speedometer reads about 10 mph more then what i going, so if it says 80 im really going 70 i was driving next to my dad on the cell phones bringing the car home and he told me how fast he was going directly in front of me roughly its 10 mph off, so i was wondering if anyone knows what gears i might have, thanks for the help

 

pull the cover and look, count teeth and do the math

 

Might be a stamping on the side of the ring gear also once you take the cover off.

 

As the guys say, jerk the diff cover and look. Numbers are stamped on the ring and pinion:

41 : 15 = 2.73
40 : 13 = 3.08
42 : 13 = 3.23
41 : 12 = 3.42
41 : 11 = 3.73

JamesC