Ok, so the other day I was researching stats on the P-38, specifically the engine. It was powered by a pair of Alison v12's, same ones as the p-40. In doing so i got off on a tangent reading about the turbos they used, and came upon this type of turbo I didn't know existed. This is called a "turbo compound". It is similar to a regular turbo in that it uses exhaust gasses to spin a turbine, although instead of powering a compressor to increase manifold pressure, it just helps to turn the crankshaft. Kind of a good idea- just route the turbo around the end of the crank and let it help out. I guess it was more complicated than it sounds because it wasnt used on too many engines. This picture is of a british Napier "Nomad" diesel aircraft engine, apparently they spent so much money on the development that it never wound up in a plane.