Does shutting down the engine affect the rate of rotation during autorotation?
with the engine disconnected from the main rotor, no torque is being applied to the rotor by the engine so there is no torque reaction trying to rotate the fuselage backwards. In this case, the only torque being applied to the fuselage is the frictional drag in the main rotor bearing, which will be small. If a tail rotor failure occurred and the fuselage began rotating because of this before the engine failure, then the fuselage will remain in rotation after the engine failure and will slowly lose rotational speed as the main rotor bearing friction acts on it.