A turbulent flame speed model based on the design and operating parameters of a spark ignition engine has been developed. The flame structure model calculates the flame speed from the flame kernel development, where the flame speed is laminar, throughout transition and turbulent flame. The turbulent flame model was calibrated against experiments carried out in an isooctane-fueled research engine running under several different conditions. The parameters varied during the tests were air-fuel ratio, engine rotational speed, ignition timing and compression ratio. Limiting conditions, where knock or incomplete combustion occurs, were also tested.