The work presents cycle models of cylinder pressure and models of forces in crank-piston system based on a sample of experimental results. The models make it possible to determine the cycles in an arbitrary state of engine operation. Model limitations and the conditions for model applicability are also discussed. An example simulation of the processes is presented for well identified and verified models pertaining to the engine of Polonez 1,5 GU automobile. The method can also be applied to other types of engines after identification of the model parameters based on a sample of at least six indicator courses measured in different states of engine operation.