773 has 115k engines. 779 has 105k engines. Both have a mgtow of 775k. It’s possible because the 779 has a larger, higher aspect ratio wing. Induced drag is inversely proportional to aspect ratio. Less drag and more lift equals less thrust required for takeoff. A more efficient airplane but will the 779 be under powered like the 773 is under winged? Footage of the first 779 flight was cool, it seemed like it barely rotated and was airborne.