The R-3350 turbo-compound engine set records for low fuel consumption by 
using the waste energy in the exhaust. Fuel consumption level were close to 
that of the more efficient diesel engines. This engine of 18 cylinderrs had 
three of these blow-down type turbines that extracted energy from the exhaust 
much in the manner of a steam turbine used in electrical generating plants. 
These turbines were coupled to the engine crankshaft through a driveshaft and 
each of the turbines added about 120 HP with no additional fuel conusmption. 
These engines were used on not only the DC-7 but the late Constellations and 
some military aircraft. These turbines also muted the engine noise.
--- FLAME v1.1
---------------