It is tractable to increase the torque for an HCCI engine and one way is to add a turbocharger. Operating in HCCI mode requires accurate control of the combustion phasing, CA50. The higher the engine torque, the narrower the CA50 window becomes where HCCI operation is maintained. As the CA50 varies stochastically between cycles this requires improved CA50 control for turbo HCCI engines. The main factors affecting CA50 is the mass/temperature of the inducted air and the residuals kept from last engine cycle. The residuals can be controlled by advancing or retarding the timing for exhaust valve closure, EVC. A turbo adds to the overall complexity due to temperature and pressure dynamics introduced over the intake and exhaust manifold. A model based CA50 controller is proposed consisting of a feed-forward and a feedback part. A linear state space model is derived from a nonlinear thermodynamic model predicting five states in the cylinder (cylinder temperature, mass oxygen, mass residuals, wall temperature and pressure). The state space model is used for constructing a feed forward filter and a LQG controller for EVC. The controller was successfully tested and evaluated in simulations.