Originally Posted by msbbarratt
The compound engines of the B29 used exhaust turbines to add more torque to the crank shaft. These engines were also supercharged by a crank driven supercharger, so you can think of them as being indirectly turbo charged. Whether that was better than simply pointing the un-tapped exhaust backwards (like Merlins did) is debatable. It was certainly heavier, more complex and less reliable. It was probably more efficient though; on a slow aircraft like a B29, jet exhaust is not as efficient as putting a bit more power into the prop.
The B-29 was not engined with the Wright R-3350 turbo compound radial. It was a standard supercharged version. The postwar Boeing B-50 was powered by the P&W 4360, but not a turbo compound version. Wright was the only company to place the turbo-compound engine into production.
The Wright turbo-compound radial was not fully developed until after the war. It was fitted to military and civilian aircraft, the Douglas DC-7 and Lockheed Constellation being two civilian examples.