Following the IAR-12's failure, the IAR team went back to the drawing board to see what could be done to boost the plane's performance, at least on this next version, designated as IAR-13.

For a second time, Elie Carafoli made no significant changes to the fuselage, but concentrated on the fin and rudder instead. Overall surface was reduced, and a oval shape was prefered this time in place of the round one previously used. The wings and the "anti-crash" pylon were retained as well, whilst the undercarriage ( which consisted on all of these projects of two main wheels and a tail "skid" ) was slightly reinforced.

The engine chosen this time was a Hispano-Suiza 12Mc, with 12 cylinders placed in a "V", whose output was close to 500 HP at 2200 r.p.m. (rotations per minute). It also offered better nose contours as well as improved forward view.For the first time, the propeller mounted was a two-bladed, all-metal Ratier one, instead of the wooden ones fitted to the previous designs. Armament consisted of the same pair of sincronized Vickers 7.7 mm machine guns firing through the propeller arc.

Test flights demostrated that the overall flying and handling characteristics had significantly improved in comparison with the IAR-12. Top speed had also been increased to 330 km/h at sea level.