Here is one of Ford's new concepts. The engineers who worked on this project explained it to me at the DEER conference.
The first time I saw this turbo I thought it looked like a coiled snake. This turbo opens and closes different chambers in order to get a better and bigger sweet spot with the boost going into the engine.
This dual volute design can spin at 130,000 rpm. I heard tales of a turbo made by the Japanese company IHI which is the size of a thumb and spins at 300,000 RPM.