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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.

Many papers are written on the frictional loss of each component in an engine, such as piston, crankshaft or bearings, but few papers describe on the total engine friction in detail. In this paper, the total engine friction is analyzed using the engine friction data of 145 HONDA mass produced motorcycle in-line engines, including single-, 2- and 4-cylinder configurations measured by the motoring method. Consequently, it is shown that the total engine friction, that is the frictional mean effective pressure (Pmf), is mainly influenced by the following dimensions; cylinder bore, piston stroke, crank pin and journal diameters. Thus the empirical equation for the total engine friction is derived, and it becomes thereby possible to reduce the total engine friction as well as to estimate it.