Opel straight-6 engine  Opel used the straight-6 engine configuration for many years. Opel used two straight-6 engines prior to the better-known CIH engine family. The Opel Moonlight roadster was the first Opel vehicle with a straight-6. It used a six in 1933. It was a 12-valve engine with a very-undersquare bore and stroke, typical for the time. This engine produced and . The 1956 Opel Kapitän was the next vehicle from the company with a straight-6 engine. This was a unit with 12 overhead valves. Bore and stroke were now oversquare for high power output at . A single Opel-designed carburetor and 7.8:1 compression yielded and .