Yeah math! also confusion...

[Featherburner]

I don't understand what you are saying with your math. What I do know is, if your speedometer read 80mph and and was correct originally and now that you changed the rear ratio and with the speedometer reading 80mph with an actual 73mph you lowered the ratio(numerically higher) than what was in there before. If you went to 2.49 gears the actual speed would be faster than the speedometer indicated 80mph.

[nateleduc]

I don't understand what you are saying with your math. What I do know is, if your speedometer read 80mph and and was correct originally and now that you changed the rear ratio and with the speedometer reading 80mph with an actual 73mph you lowered the ratio(numerically higher) than what was in there before. If you went to 2.49 gears the actual speed would be faster than the speedometer indicated 80mph.

Speedo worked perfectly before. I am using my GPS to determine my speed. When I had my 3.42s (stock) my gps speed was spot on. Now that I swapped this mystery rear end in, I tuned it for 2.73s. When driving 80mph according to my speedo, my GPS says 73.

[Featherburner]

Speedo worked perfectly before. I am using my GPS to determine my speed. When I had my 3.42s (stock) my gps speed was spot on. Now that I swapped this mystery rear end in, I tuned it for 2.73s. When driving 80mph according to my speedo, my GPS says 73.

Tune for 3.08s and you will be good. Is this a 4th gen fbody?

[nateleduc]

yes sir