This paper* describes a combined analytical and experimental hardware-in-the-loop powertrain systems analysis methodology. Central to the implementation of this methodology is a real time dynamic system simulation computer such as the high-speed Applied Dynamics Model AD10. For automotive engine control system studies, wide bandwidth in-cylinder combustion pressure sensor signals are input to the AD 10 computer. Control commands are calculated and communicated at high data rates to throttle valve, spark ignition, and fuel injector actuators. Both simulation and experimental results are presented. Using this approach, the functional improvements associated with various control philosophies can be determined.