A powertrain system includes a cylinder deactivation system mechanically coupled to an internal combustion engine, and electrically coupled to an engine management system. The engine management system signals the cylinder deactivation system to selectively deactivate one or more engine cylinders. The engine continues to operate using the remaining available active engine cylinders, and generates an inconsistent torque output. A torque-smoothing device mechanically coupled to the engine, and electrically or hydraulically coupled to an energy storage device, removes and releases energy periodically to compensate for the inconsistent torque output.