Reducing friction in the Piston-Cylinder Unit - PCU is one of the priorities in the automotive industry as it is the largest contributor to the frictional losses and hence the fuel consumption of the internal combustion engines. Not only fuel consumption, but also the oil consumption and emissions are largely affected by the piston-ring-liner interactions. Therefore, from an optimized PCU, competitive, economic and environmental benefits would be gained.  In this project, fuel/oil consumption and emissions of car and truck engines were reduced by using different cylinder liner finishes and different ring designs/loads. Experimental and theoretical studies have been performed by simulating and testing the behaviour of various oil control rings and cylinder liner surfaces in reciprocating tribotesters. Several full-scale engine tests were performed to verify the improvements. The engine tests showed up to 1.8% reduction of the fuel consumption while keeping low oil consumption by using smoothly honed liner surfaces and low ring loads/widths. Further reduction of the oil consumption was shown in the tribotests and simulations when textured liner surfaces were used. To accomplish this, a cost-effective texturing process has to be found and to be confirmed in the engine tests.