Ok I have an 85 Z28 5.0 tpi with a 700R4 and an open diff, not sure of the ratio but probably wimpy.

My speedometer ends at 85 mph. In 1986, the speedo stopped at 140??? But from what I have learned, there were very minor changes between 85 and 86 if any! So whats the deal? how fast can I go?

I have driven to the point where my needle almost looped, hits against the trip odometer reset button and stays pressed against it while I floor it. It seems as if I'm doing about 120 - 130 but I dont know. I also dont have anyone close enough or crazy and fast enough to drive along side me and let me know. So how can I tell OTHER THAN HAVING A COP TELL ME WHILE BENT OVER HIS HOOD!?!?!?!?!?!?

No major mods yet but I stripped the AC, smog pump, and cruise control unit, minor porting to the plenum, small tube headers, dual exhaust with no cat, homemade cold air/ram air intake and a fiberglass hood.

Gimme your guesses guys! thanks!

 

Your top is probably right around 140 MPH, give or take a couple of MPH if you have the 2.73:1 rear gearing.
Find your rear gear ratio, then use the calculation to determine your speed.

RPM = (MPH * (gear ratio * 336)) / tire diameter in inches

or

((RPM / (gear ratio *336)) * tire diameter = MPH

In 3rd gear in a 700R-4 trans and a 2.73:1 rear gear, at 5000 RPM with a 26" diameter rear tire your speed would be 141.7 MPH.

 

For a while a law was passed that speedometer's could only read up to 85. They thought if it only read 85, people would only go 85. Didn't quite work out.

 

Funny that your speedo stays pin against the trip reset. The one in my 88 continiually bounced off of the trip reset.

I had a 350TPI and 2.73's, when I was in germany my buddy was in his 535 bmw next to me and his speedo said we were doing 260 KPH about 160 mph. I put the valve that keeps you in OD till the car is damn near floored, took a few miles to get going that fast though!