The Franklin O-175 (company designation 4AC-176) was an American air-cooled aircraft engine of the 1940s. The engine was of horizontally-opposed four-cylinder and displaced 175 cu in (2.9 L). The power output was nominally 80 hp (60 kW). A later variant was designated O-180, despite sharing the same displacement. A related four-cylinder engine of slightly smaller capacity was known as the O-170 or 4AC-171. It produced 60 hp (45 kW).