There is math behind that Mongrel. The formulas needed are generally listed in the Rotarycraft Handbook. I beleive (been a while) minimum operation time is 0.05secs. Plug that in with the minimum torque requirement, and solve the equation.
EDIT: I should point out, some machines work slightly differently, for instance the Friction heater works best with an even amount of speed and torque.
EDIT: I should point out, some machines work slightly differently, for instance the Friction heater works best with an even amount of speed and torque.