At present the market of Wankel engines is limited to some special applications. This fact explains absence of commercial software products specially developed for this engine simulation and prediction of its performance. Conversely, there are available and widely used software products for simulation of reciprocating-piston engines performance. Some attempts are known in using this software for prediction of Wankel engine performance. This paper details an approach used in these attempts. Main differences between both types of engines are summarized and principles of a virtual reciprocating-piston engine compilation are developed. A method of virtual blowing was developed for assessment of discharge coefficients for intake and exhaust ports. Comparison of simulation results with the measured performance of two UAV Wankel engines showed sufficient accuracy of the suggested approach.