> No turbocharger is used, but a small Roots-type supercharger expands the compression ignition window by adding more air to the engine to allow leaner fuel mixes – especially at higher speeds where avoiding knock is more problematic.

This is a surprising engineering decision considering the efficiency goals. I'd be curious to see how they managed to offset the parasitic losses. In a hellcat engine, the supercharger consumes anywhere from 10 to 100hp depending on engine load. You can never turn it off.

The Hellcat uses a massive twin-screw compressor. A Roots type supercharger is a blower, that is, a positive displacement pump with no internal compression that can run pretty efficient. Mazda's unit is comparatively small and clutched, so they can turn it off when not needed.