Originally Posted by
A Squared
Pratt and Whitney manufactured a whole bunch of different radial engines with 2800 cubic inches of displacement. Some models are pretty dissimilar with no interchangeable parts The engines installed on the Convair were almost certainly either CA series or CB series engines, both of which had a drive ratio of 9:20 or .45:1 Reference is the Type Certificate Data Shees for the respective engine series.
As a former USAF C-131D (340-79), it would likely have been fitted with CB series engines (CB3/CB3/CB16/CB17), in which case the reduction gear would be 0.45:1.