the two stage hydraulic supercharger is old news. That technology was deveolped for the aviation industry twords the end of WW2 when the piston engine was almost obsolete due to the introduction of the turbine engine.
It was widely used in high speed high altitude fighters and bombers.
They were very effective, in fact so much so that if the pilot accidentally selected high blower any lower than 10,000 feet the engine would be over boosted so much so that the cylinders would blast themselvs out of the crankcase in the succession of firing order.
