what does 90 on my speedo = when i have 3.73s

[BlueOvalStangGT]

i got pulled over yesterday on the way home from the track and my speedometer said 90 but i haven't changed the speedo gear yet. he didnt write me a ticket but he did call my parents and said i was RACING my freind(drives a zx2) and was going 85-90. he caught up to me from behind and theres no way i was going 90 and we were definitly were not racing. help me out, what does 90 on my speedo = to actual speed

p.s. parents are trying to take my car away for 2 months about this

 

[Rootus]

By my calculation:

90 mph == 79 mph if your original gears were 3.27.
90 mph == 74 mph if your original gears were 3.08.
90 mph == 66 mph if your original gears were 2.73.

Dave