The Lycoming IO-720 engine is a large displacement, horizontally opposed, eight-cylinder aircraft engine featuring four cylinders per side, manufactured by Lycoming Engines.
There is no carburetted version of the engine, which would have been designated O-720 and therefore the base model is the IO-720. The IO-720 and the Jabiru 5100 are the only flat-eight configuration aircraft engines currently in production.
Read more about Lycoming IO-720: Design and Development, Variants, Applications, Specifications (IO-720A)