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Internal combustion engine due to Thermodynamics deliver output of 25% of the input fuel energy. Hence £75 out of every £ 100 invested in fuel in an engine is lost in the form of emissions, vibration, or heat di ssipation. Mechanical losses in an IC engine are referred to as " parasitic losses", which account for 15% of the total losses. There is a possibility for reducing these losses through appropriate remedies. The piston assembly is a common contributor to the mechanical losses. This could be as high as 45% of it. A typical piston assembly consists of a compression ring, a scraper ring and an oil ring mounted on the piston body. The most significant loss in the piston assembly is from the ring pack and cylinder bore interaction and can account for 80% of this. Two thirds of the total loss due to ring pack is contributed by the compression ring. In the process of simultaneous sealing and reciprocation, a compression ring is subjected to modal stresses, which imparts radially a outward force, in-plane, out-of-plane bending moment and twisting moment; as well as axial flutter and twist. The radial deformation of the ring and the issue of ring-bore conformability are important, and are addressed in the current analysis, which deve lops a tribo-dynamics model of the compression ring and cylinder liner conjuction. As part of the lubrication modelling, an isothermal model is developed to estimate frictional losses, initially with a consideration of asperity interaction and viscosity pressure dependency, when solving Reynolds equation. Further improvements include the effect of roughness on flow behaviour of the lubricant. Both of these approaches are combined for a transient analysis. The results are compared with measurements from the literature and good agreement is found. The novelty of the current research is the combined solution of Reynolds' equation, and the energy equation using appropriate rheological behaviour for evaluating the key lubrication performance parameters such as pressure, temperature, viscosity, minimum film, friction loss, also considering asperity interaction for a globally deformed compression ring.