Extreme engine downsizing is a modern solution aimed towards the goal of meeting new emissions regulations for internal combustion engines. A higher percentage downsized engine will produce less CO2. By extension, a higher boost level is required to generate high engine torque performance. The transient load step of a higher boost system at low RPM is currently an issue for conventional boosting. Aeristech has developed an electric supercharger to be matched with a conventional turbocharger to create a new type of two stage boosting system and a simpler downsized gasoline engine usable in mainstream vehicle segments.Whereas most electric pressure charging devices are capable of transient output to alleviate turbo lag. The electric supercharger is capable of steady-state air delivery. This makes the electric supercharger a dual-function device, alleviating turbo lag and also supplementing the compressor map of the turbocharger or main boost device. The electric supercharger thus acts as a conventional mechanical supercharger in addition to a conventional electric pressure charging device. Accordingly, the electric supercharger can replace a turbocharger stage within a multi-stage turbocharger arrangement. This functionality was simulated on a 2L boosted premium gasoline engine , and tested on a 1.2L extreme downsized engine .There are currently two primary designs of electric supercharger: one uses separate motor and power electronics and the second incorporates the electronics as a single package. The compressor alone achieves a wide map width and 80% peak efficiency whilst the combined motor and power electronics are able to deliver full load in less than 0.5s. The design was optimised to minimise the specific volume and to improve packing flexibility within the vehicle.In addition, the electric supercharger has been tested on MAHLE’s electric supercharged Di3 engine. This engine produces high specific power of 161kW/L and a substantially flat torque curve across the engine’s speed range .