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Changes in engine emission regulations created very difficult ground for piston engines. On one hand current emission norms require very big reduction of HC, NOx and PM emissions followed by huge pressure on CO2 emission from cars tailpipe. On the other hand customers expect that their LEVs will not suffer performance downgrade. Engine engineering society all around the world need to deal with contradicting targets: customers expects continues performance upgrade but that needs to be combined with mandatory emission reductions. For some past years downsizing was considered as perfect solution that due to advanced turbocharging and/or supercharging systems made it possible to provide low emissions and high performance. However this was solution that worked only under certain conditions and the gap on emissions between real world driving and tests run in laboratory is huge mainly due to completely not matching driving conditions and, even more important, drivers personal driving style. In general downsizing is built on solid ground: emissions can be reduced without suffering engine performance if efficiency is increased. Turbocharging is one of the solutions helping to increase efficiency, but some companies survived with spark-ignition engines without turbocharging and still provide cars with low emissions and good performance. This article will evaluate various solutions of efficiency improvements. This review will be then followed by tests results from variable compression ratio engine equipped with advanced control system. Tests will determine influence and correlation between engine control settings and its efficiency.