Systems and methods are provided for applying lengthwise curvature to composite parts. One embodiment is a method that includes fabricating a preform for a curved pultruded gap filler by continuously: heating fiber reinforced material to a sticking point temperature for a constituent material within the fiber reinforced material, and feeding the fiber reinforced material through a die that exhibits a curvature through which the fiber reinforced material travels while the fiber reinforced material is heated to the sticking point temperature, the die forming the fiber reinforced material into a preform for a gap filler. Fabricating the curved pultruded preform further includes varying path lengths of fibers within the preform as the preform passes through the die, and pulling the preform out of the die.