During car services, it is sometimes necessary to measure the effective performance of the engines. After repairs it is very useful to check the change of the performance. In this case you don't have possibility of dismantling. You can measure the vehicle on roll benches. In this case you have so-called wheel performance as result. The new method discussed and described in this article provides a solution to this problem. The paper contains the theoretical and practical introduction of the measurement of engine performance with diagnostic measurement processes.