revtime

iTrader: (1)

2.73 gears mandated lock out of first gear. period.
There possibly is a Z28 out there with the GU5 (3.23) and the lower MPH cluster, which means it did not come with Z rated tires.
Anything is possible. Not very probable that a performance axle ratio did not come with Z rated tires however.

the_merv

iTrader: (88)

I have the 150 Speedo, and there is a peg on it, if you drew it out, it would be at 165-170ish, I don't know how accurate it is at that speed, only had it there once..

SprayedLT1

iTrader: (8)

It's because you have 2.73 gears. Gear ratios have no impact on anything like the speedo.

All cars with 2.73 gears have the 1st gear lockout.
All cars with Z rated tires have the 155 mph speedo

Feenix

Those with 3.23 would be 93 m29 cars. 94+ came standard with 3.42 if it was an m6.