I recently put a Dallas Speedcal unit in my '96 Auto w/3.73 gears. My speedo is reading 30mph and i'm getting a gps reading of 38mph. Anybody good enough with these to give me a useable code? I called Dallas Mustang and Justin told me that they didn't know how to calculate the codes that way and I would just have to "play" with it.

 

I ended up having to play with mine. Errrr... Speedcal that is LOL. Go to http://www.dallasmustang.com/page/speedcal.calc.php and put your info in. It will then you give you a binary number back to change in your speedcal. FYI.... 1 is on 0 off. I ended up having to go to 3.08 gears to get mine right because I also got 17x9 rims as well as 275x40x17 tires. Play with that and see if it gets you close.