Abstract: An adjustable mass cam arm for use in a rotary speed regulation device such as a belt drive torque converter is described. The cam arm has a base region and an elongated centrifugal mass region extending therefrom, the centrifugal mass region terminating in a proximal end which is attached to the base region. The cam arm has an internal cavity which in turn has a cavity opening which is located in the proximal end of the centrifugal mass region, and is readily accessible when the cam arm is installed in the torque converter. Mass can be installed in the internal cavity to add mass to the cam arm, thereby allowing for changing the moment of inertia of the cam arm. In a preferred embodiment, the internal cavity is elongated, and one or more weights are provided, having different masses and/or densities, for selective installation into the elongated cavity. In another further preferred embodiment, the elongated cavity and the one or more weights are threaded.