Second batch of aircraft were upgraded by replacing the IAR K14 engines with 1200 hp water cooled Junkers Jumo 211Da engines increasing the maximum speed from 350 km/h to 405 km/h. Eight of these new airplanes were ordered in Italy. They were designated JIS-79B (Jumo Italian S-79B). But they didn't arrive until August 1941. An additional 36 aircraft were license built in IAR factory in Brasov under designation IAR 79 JR (Jumo Romx�n).
The IAR.79 was a cantilever low-wing monoplane bimotor, with a retractable taildragger undercarriage. The fuselage of the IAR.79 was made of a welded tubular steel frame and covered with duralumin in the forward section, duralumin and plywood on the upper fuselage surface, and fabric on all other surfaces The wings were of all-wood construction, with the trailing edge flaps and leading edge slats (Handley-Page type) to offset its relatively small size. The internal structure was made of three spars, linked with cantilevers and a skin of plywood. The wing had a dihedral of 2� 15'. Ailerons were capable of rotating through +13/-26�, and were used together with the flaps in low-speed flight and in takeoff. Its capabilities were significantly greater than its predecessor, the SM.79, with over 1,850 kW (2,800 hp) available and a high wing loading that gave it characteristics not dissimilar to a large fighter. The engines fitted to the main bomber version were two 750 kW (1000 hp) IAR K14 radials, equipped with variable-pitch, all-metal three-bladed propellers. Speeds attained were around 430 km/h (270 mph) at 4,250 m (13,940 ft), with a relatively low practical ceiling of 6,500 m (21,330 ft). Cruise speed was 373 km/h (232 mph) at 5,000 m (16,400 ft), but the best cruise speed was 259 km/h/161 mph (60% power). The landing was characterized by a 200 km/h (120 mph) final approach with the slats extended, slowing to 145 km/h (90 mph) with extension of flaps, and finally the run over the field with only 200 m (656 ft) needed to land (2,050 rpm, 644 Hg pressure). With full power available and flaps set for takeoff, the SM.79 could be airborne within 300 m (980 ft).