[sidney]

An exhaustive account of the differences between the Bf 109 F-4 and F-2 you can find in Prien & Rodeike book entitled Messerschmitt Bf 109 F,G & K - An Illustrated Study, pages 24 to 29. They said that the early versions of the Bf 109 F-4 differed little from the Bf 109 F-2 externally. With the production development, the supercharger air intake was changed with the noticeably increased diameter and more sharply curved shape.