The Lycoming IO-233 is a non-certified four-cylinder, air-cooled, horizontally opposed piston aircraft engine that produces between 100 hp (75 kW) and 116 hp (87 kW).

The Lycoming O-235 is a family of four-cylinder, air-cooled, horizontally opposed, piston aircraft engines that produce 100 to 135 hp, derived from the earlier O-233 engine.