Rack and pinion how to figure torque and pitch angle why 14 deg

I know how to calculate the torque by belting or gearing what are
the equations for a rack and pinion. Also why you have to use 14 deg
There seams to be more selection at 20 deg.The Motors I have are
Small and I need to be able to move the gantry head at
800 inch per min I building a burn table and want to use rack and
pinion I need to know how much increase in torque using what pitch
gear on the pinion.
Thanks Randy