A well-known engine of this type is the Porsche air-cooled flat-8 engine. It was introduced as a 1.5 litre engine for Formula One, and grew to a 3 litre version used in the Porsche 908.[citation (source) needed]
Another example is the Australian-made Jabiru Aircraft5100. This is a 5.1 litre, air-cooledaircraft engine.
Continental and Lycoming have both produced flat-8 aircraft engines. The Lycoming IO-720 and Continental IO-720 series of engines have been in production for several decades.