Motorsport constitutes an excellent research laboratory for the entire automotive industry and all the related industry branches. Since the dawn of motorization, motor vehicle component systems have been developed and improved. This process will go on and there is no doubt that it will never stop. Engines with rising performance require increasing strength of transmission system components. The more efficient use of the power transmission system requires improvements in the suspension system, which will ensure better vehicle handling, and higher efficiency of brakes, so that the vehicles moving with higher and higher speeds can be stopped more effectively. An increase in the cruising speeds entails a higher accident hazard and this, in turn, requires safer construction of the vehicle body. The best way to develop the modifications is to test them in the difficult conditions of professional motorsports. The solutions engineered for this purpose and proven on such a kind of testing ground are afterwards adapted to mass-produced vehicles and used in everyday vehicle operation. This publication is to present the scope of the work to be done when building a high-performance sports car that must meet the requirements of regulations laid down by FIA (Federation Internationale del'Automobile) for vehicles of this type. The works described in this article were undertaken to modify the construction of a mass-produced Renault Clio car of the second generation in order to adapt it for professional motorsports, chiefly for starts in Polish and international rallycross championships. The modifications of this car intended for rallycross racing consisted in the designing or modernization of its individual parts and component units so that they were compatible with the specificity of this sport and were in conformity with FIA requirements.