Random thought about past aero engines.... I found this on a different forum & randomly thought some here might be interested....
"Another funny one..... is to pass the engine-turbo exhaust through a mechanically coupled 'turbo' (200 : 1 or so) to the flywheel . . .
The last generation of piston aeroplane engines used this, referred to as "turbo-compounding". The most successful of these was the Wright R3350 eighteen cylinder radial, which used three exhaust turbines coupled to the crankshaft via fluid couplings to raise power from 2800HP to 3500HP and at the same time reduce specific fuel consumption. More ambitious was the Napier Nomad, which was a twelve cylinder turbo compounded two stroke diesel of similar power, but much better figures for power/weight and specific fuel economy, as well as lower frontal area. 70% of the power came from the turbine. However, by the time it came on the scene, aircraft manufacturers and buyers were only interested in turbines, and it never got beyond a prototype. "
I presume it is factual, and my mind got tied in knots trying to visualise the mechanics of those motors.