A method for controlling engine operation, the engine having a turbocharger coupled between an intake and exhaust manifold of the engine via a turbocharger shaft, the method comprising dynamically determining turbocharger shaft speed based at least on intake and exhaust manifold conditions using a torque balance across the turbocharger; and adjusting turbocharger boosting to adjust turbocharger shaft speed in response to said dynamically determined turbocharger shaft speed.