Wow never heard of these
Following the war, in order to better serve the civilian market, the Turbo-Compound[2] system was developed in order to deliver better fuel efficiency and thus economy ("gas mileage"). In these versions of the engine, three power recovery turbines (PRT) were inserted into the exhaust piping of each group of six cylinders and geared to the engine crankshaft by fluid couplings in order to deliver more power (rather than by using the exhaust to deliver additional boost as in a turbocharger). The PRTs recovered about 20 percent of the exhaust energy (around 500 HP) that would have otherwise been wasted, but unfortunately had a negative effect on engine reliability, causing many aircraft mechanics of the day to nickname them "Parts Recovery Turbines" (and worse). The failures concerned would probably have been of exhaust valves and related parts since the turbines would have both increased backpressure & increased the operating temperature of the exhaust valves causing greater wear and failure.[citation needed]
Straight from wiki