Difficulties in development of the Foka engine led to the second prototype, the P.38/II, being fitted with two 450 hp Ranger SGV-770B twelve-cylinder engines. This aircraft flew in May 1938, the first prototype with 620 hp Foka II engines not flying until January 1939. In the meantime, a more refined development of the basic design, the P.48 Lampart (Leopard) powered by 700 hp Gnome-Rhone 14M Mars radials, had succeeded the Wilk in future planning, but prototypes had yet to be completed at the time of the German invasion of Poland. The following data relate to the Foka II-powered Wilk prototype.
Span: 36 ft 3 in (11.05 m)
Length: 27 ft 4.75 in (8.35 m)
Height: 8 ft 2.5 in (2.50 m)
Wing area: 204.52 sq.ft (19.00 sq.m)
Empty weight: 3, 781 lb (1,715 kg)
Loaded weight: 6,107 lb (2,770 kg)
Max speed: 289 mph (465 km/hl at 13,125 ft (4000 m)
Range: 777 mls (1,250 km)."