An experimental research car that runs at over 300 km/h has been developed by aerodynamic improvement. To achieve this target with 295PS, 2000cc engine, a coefficient of drag CD = 0.20 was required. The results of basic research and some fundamental aerodynamics are described. Particularly, a base-bleed system using engine cooling air has been investigated from the results of basic tests of a simple model. A new method to determine the curvature of the body-surface corner is proposed, on the basis of the prediction of a turbulent boundary layer separation for the front part of the body. The various processes of aerodynamic improvement in the wind tunnel are explained. It is suggested that this kind of approach is of indispensable process for developing an aerodynamically efficient vehicle.