In this paper we suggest the use of knowledge based configuration in connection with CAD systems to enhance the ability of reusing models of CAD components and to automate solution processes especially of variational design problems. Configuration systems can support design engineers in choosing components and in checking consistency. We have investigated how configuration mechanisms can be applied to the design of engineering products and introduce our heuristic relevant knowledge first (RKF). This heuristic solves many of the problems which occur with configuration in engineering domains which continuously change, e.g. as a consequence of innovation. We conclude with the presentation of experiments performed with RKF.