Because the airplane was designed expressly for the IO-390, Pipistrel had to go back to the drawing board. The company decided to replace the IO-390, four-cylinder engine with the Lycoming IO-540-V six-cylinder. The move has forced the company into a redesign phase to allow the Panthera to accommodate the heavier and larger IO-540, which has 150 cubic inches more displacement than the IO-390-A and develops 260 horsepower (50 more than IO-390-A) while weighing 110 pounds more than the four-cylinder model. The IO-540 is also eight inches longer than the IO-390. According to Pipistrel, the first aircraft with the new engine will be ready for testing "this year," though the Slovenian company did not precisely specify the new timeline and delivery schedule.