addTorque function - limited energy?


i have a question concerning the addTorque funtion of a PxRigidBody.

I have written a small penulum program, where a long box is fixed to the world through a revolute joint at one end of the box. It can swing around freely (gravity is off). I can stop it from swinging, so the angular velocity around all axes is 0.
Now torque is added through the addTorque function, for example (1.0, 0.0, 0.0) because it is swinging around the x-axis. If a certain value is reached, it seems like the impact is limited. It does not matter if (50.0, 0.0, 0.0) or (80.0, 0.0, 0.0) is applied, the resulting angular velocity is the same. If the size of the long box is varied, the resulting angular velocity varies too. The maximum angular velocity of the actor is set to 1000, so this can be ruled out as a cause.

Can someone explain, why this is like it is?