The optimal design of the motor dimensions, the capacitance of the run capacitor, the winding distribution and the choice of the electrical steel are the most important sources for an improvement of the efficiency of modern single-phase induction motors for given performance and material cost constraints. The formulation of the techniques which realize this optimization is based on nonlinear programming approaches. The Method of Boundary Search Along Active Constraints is used for the optimal design of the motor dimensions of a commercially available 2 hp, 115 V single-phase induction motor. Based on the optimization results due to the above mentioned four optimization components, the relationships between efficiency, power factor, cost, active materials and the values of the capacitance of the run capacitor are studied and the limited validity of the model law is discussed. This report also explains why the Wanlass retrofit improves efficiency and details the advantages and disadvantages of such a retrofitting as compared with the operation in the standard configuration.