Opel began production of automotive straight-six engines in 1927 with a 1.8 litre flathead engine used by the Opel 8/40 PS. The displacement of this engine was expanded as it was used in later models such as the Opel Kapitän and Opel Admiral, with later versions switching to an overhead valve (pushrod) design. In 1968, the straight-six versions of the Opel CIH engine were introduced, initially using a single overhead camshaft (SOHC) with some later versions using double overhead camshafts (DOHC). Production of the Opel CIH engine continued until 1993, when it was replaced by a V6 engine.