on the SCT Xcal3 what will i be able to modify on my own? like switch from diff things when i do diff things to the car. lets say can i switch it from cats to o/r(no cats)? from longtube headers to short tube headers? from diff octanes? the wheel sizes? will it let me turn on and off sensors?

 

The adjustably really is dependent on the year and model of your Mustangs. Certain features were not computer controlled until later models, for example, gears and odd tire sizes can only be adjusted on 1999 and newer Mustangs because the car's computer did not control the gauges before that year.

Fuel Octane is dependent on the custom tune itself, IE you would need a tune made just for 93+ octane, etc. The X3 does have 87+, 91+, 93+, and fuel economy tunes built-in to its pre-loaded tunes if you are not going the custom tune route.

That said, some common adjustments are Rev Limiters, Speed Limiters, Automatic Shifting Adjustments, Spark, and Air/Fuel Ratio.