ProjectStang

I am getting ready to have 3.73 gears installed in my auto 98 GT? How far off will my speedometer be? What programer would be the best to correct it?

thanks
Rob

The Great Cornholio

I don't know what your stock gear ratio is, but if it's 3.27 the speedometer will read about 14% higher than it should when you install 3.73s. It's a simple ratio of 3.73/3.27 X speed, so for instance if you're actually going 60 mph your speedo will show 68 mph after installing 3.73s. If your stock ratio is 2.73, the speedo will read 82 mph after installing 3.73s when you're actually going 60 mph. If you dont know what your stock or current gear ratio is, jack up a rear wheel and count the approximate number of revolutions of the drive shaft per one revolution of the wheel, and compare that to known Ford gear ratios (2.73, 3.08, 3.27, 3.55, 3.73, 3.90, 4.10, etc.).

If you have a manual transmission you can correct the speedometer with a SpeedCal or a programmer. If it's an automatic a programmer will be required to correct it. I use a Diablo Predator, and Superchips also makes a programmer I have used. Both are good tuners, and there are probably several others as well that might work on a 98, including HyperTech and SCT.

ProjectStang

Thanks for the help.