Part of the reason uncorked rotaries are so loud is that some fuel leaves the engine unburned and that fuel is still burning in the exhaust. That burning fuel is lost when the engine is naturally aspirated, but when you bolt on a turbo it's using those burning gases to turn the turbo. You can put pretty massive turbos on pretty small rotary engines, and they have no problem spooling them.Unburned fuel is unburned fuel is fuel wasted. Unless there's a supplementary source of ignition between the port and the turbo, that unburned fuel is lost.