<div class="htmlview paragraph">For the prediction of frictional mean effective pressure (Pmf), the experimental data of over 300 engines, including super high speed engines whose maximum revolutional speeds were up to 16000 rpm, were analyzed. It was found that Pmf is nearly proportional to a non-dimensional number given by piston stroke (S), mean equivalent crank diameter (Dcm) and cylinder bore (B). Its proportional constant consists of an engine speed dependent term and a constant term. We focused on the influence of pumping loss on the first term and made a tribological study on the second term. As a result of this research, regardless of cylinder configuration or maximum engine speed, Pmf can be estimated at the stage of engine designing.</div>