What about a small displacement engine for economy during stop and go traffic jams.
During uphills, passing or otherwise called to make serious power it would have an electric supercharger passing air thru an Oxygen concentrator
Oxygen concentrator - Wikipedia, the free encyclopedia
The Oxygen concentrator feeds Oxygen enriched air to the engine allowing more fuel to be burned thus being capable of generating much more power for a given engine size. Even more power than a turbo engine of the same displacement.
It remains to be seen if such high Oxygen concentrations would make the engine any more prone to predetonation although I suspect air temperatures would be more important than Oxygen content.