This new approach for improving fuel economy uses computer programs to optimize and tailor an engine's fuel, EGR and spark control in the laboratory. New forms of engine and vehicle test data are used as inputs. This includes a simple simulation of the catalytic converter. The emission engineer is in control of the process via a special interactive program at a computer terminal. He combines his know-how with the computer programs to create a feasible engine control calibration for vehicle evaluation. The programs can also be used to study tradeoffs of optimized fuel economy vs emissions for a vehicle. Although presently limited to warmed up operation, the optimization procedure has proved to be valid and useful.