The F.4 was to be powered by a 960 hp Isotta-Fraschini Asso 121 RC.40 Vee engine, but late in construction it was decided to replace that with a 1,175 hp Daimler Benz DB601A. This change delayed the F.4’s completion into 1940, but flight trials revealed the F.4 to possess good performance, excellent maneuverability and first class handling characteristics.