From what I can determine, there were two engines considered when the B-24 was designed, the single row Wright R-1820 and the twin row Pratt & Whitney R-1830. Since the 1820 was already in use on the B-17, the B-24 was designed to use the R-1830. And all operational versions continued to use that engine until the mid 50's. (Most of the latter were the Navy's PB4Y-1 and -2. The 4Y-2 models had the biggest diffirence in the engines. They still used the R-1830 engines but without the external mounted turbochargers.