The techniques for optimization of fuel economy in the design of the new GM 1980 “X” cars involved reduction of road load and parasitic losses combined with power train matching to the vehicle as a system. Computer simulations identified potential fruitful areas of economy improvement. The method of establishing meaningful targets for weight, aerodynamics and tire losses is described. Matching of engine displacement, torque converter characteristics and transmission and axle gearing to the vehicle system made possible the minimum engine size consistent with target performance requirements. It is concluded that the methods employed made possible a high level of fuel efficiency relative to both vehicle size and performance.