Hi again, I installed 3.73 gears on my 93 z28 6speed. I was wondering if anybody knew the actual speed I'm going if for example the speedo marks 40mph. I have parts on order to fix the speedo but I don't wanna risk getting pulled over. Thank you.

 

Depending on tire diameter, there is a formula. I am sure Injuneer knows it. But you will need to supply the tire size/diameter.

Another way is if you or a friend has a GPS, they will give you mph while you are moving, or have a friend drive along side you and relate the info.

 

GPS/smartphone w/GPS app.
Assuming you had 3.42s',changing to 3.73s' will indicate a higher MPH than actual. At 65MPH speedometer reading you're actually going 60MPH.

 

Problem is the 1993's were the only year that the T56 didn't come with 3.42's. They either had 2.73’s (GU2) or 3.23 (GU5) depending on whether it had the wide ratio (M28) or standard ratio (M29) version of the T56.

Check the service parts label for those RPO codes.

Starting with 2.73’s, multiply indicated speed by 0.73

Starting with 3.23’s, multiply indicated speed by 0.87