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Two of the objectives in developing internal-combustion engines are to keep wear and - at the same time - the related friction losses between the piston rings and cylinder liner as low as possible. To this end, optimization of the hydrodynamic conditions and designing for reduction of mixed friction have become the goals of many engine manufacturers and developers. As part of this project, a two-dimensional computation model is developed to include modelling of four areas: gas dynamics, lubrication-oil hydrodynamics, solid-body contact, and piston-ring dynamics. The gas pressures in the ring pack are calculated either using the one-dimensional Navier-Stokes equation or the unsteady adiabatic-flow model. The hydrodynamic pressure distribution ranging from the piston-ring running surface to the cylinder wall is calculated by solving Reynold's differential equation for rough surfaces /1/. This was accomplished under the use of flow factors.