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Spark ignition engines have low efficiency when working at part and light loads. This can be opposed by using a slightly different thermodynamic cycle known as Miller cycle. This cycle can be implemented in conventional engines if they are equipped with systems providing variable valve timing and variable compression ratio. A computer model to simulate internal combustion engines is used to generate and characterize in terms of torque and brake specific fuel consumption, both Otto cycle engines and Miller cycles engines with VCR. These engines are used in a second computer model to generate the European driving cycle, using the same car and the same gear box, in order to evaluate its performance in terms of fuel consumption. Different ratios for gear boxes using the Miller cycle are proposed in order to achieve a more efficient car (engine, gear box, structure), with less fuel consumption and less green house gas emissions for the urban driving operation.