As engines are equipped with an increased number of control actuators to meet fuel economy targets they become more difficult to control and calibrate. The large number of control actuators encourages the investigation of physics-based control strategies to reduce calibration time and complexity. Of particular interest is spark timing control and calibration since it has a significant influence on engine efficiency, emissions, vibration and durability. Spark timing determination to achieve a desired combustion phasing is currently an empirical process that occurs during the calibration phase of engine development. This process utilizes a large number of stored surfaces and corrections to account for the wide range of operating environments and conditions that a given engine will experience. An obstacle to realizing feedforward physics-based combustion phasing control is the requirement for an accurate and fast combustion model. In this research, a quasi-dimensional turbulent flame entrainment combustion model for the purpose of real-time combustion phasing prediction is proposed. The proposed algorithm utilizes existing engine sensors and calculates combustion phasing from a physics based model in real-time. Transient engine dynamometer results using a rapid-prototype engine controller demonstrate a prediction accuracy for the location of fifty percent mass fraction burned (CA50) within 3.6 crank angle degrees.