The Subaru EA engine was introduced in 1966 and began Subaru's line of boxer-four engines that remain in production to this day. Most of Subaru's models are powered by a boxer-four engine in either naturally aspirated or turbocharged form. A print ad for the 1973 Subaru GL coupe referred to the engine as "quadrozontal" The company also produced boxer-six engines from 1988–1996 and 2001–2019. In 2008, the Subaru EE engine became the world's first passenger car diesel boxer engine. This engine is a turbocharged boxer-four with common rail fuel injection.