An engine system including a power plant, an intake assist device connected to an air inlet of the power plant, and an expander connected to an exhaust outlet of the power plant is presented. A motor/generator is connected to power the expander to selectively provide power to and capture power from the expander. An expander controller is connected to control the motor/generator connection to the expander, and is configured to select between a passive mode, where exhaust passively moves through the expander, and an active mode, where the motor/generator powers the expander to actively draw exhaust from the exhaust manifold. In one example, the air intake and exhaust flows are controlled independently of the rotational speed of the power plant.