An internal combustion engine including at least one cylinder having a central axis and a variable ration crankshaft assembly employed to extend a dwell point of a piston and improve connecting rod leverage. The crankshaft assembly comprises a gear set having a gear ratio 1:1 and including a first gear member non-rotatably mounted to an engine block and meshing a second gear member drivingly coupled to an eccentric member rotatably mounted between to a crankpin of the crankshaft assembly and a connecting rod, defining an offset lever extended between axes of rotation of the eccentric member and a lower end of the connecting rod connected to the crankshaft assembly. The eccentric member is positioned on the crankpin so that the offset lever is perpendicular to the central axis when the piston reaches TDC. Such an arrangement allows extending a dwell point of a piston and improving connecting rod leverage, thus increasing efficiency of the mechanical conversion process. The invention is applicable to both two- and four-stroke cycle engines.