Introduced in 1995, the Ford Sigma is a small straight-4 automobile engine sold by Ford Motor Company. First evolution of engines were sold as the "Zetec-SE" (although frequently badged as Zetec-S, not to be confused with the trim level). After the upgrade Ford renamed Sigma to Duratec. Last upgrade of engine is named Duratec Ti-VCT. The engine was introduced in the mid-1990s and production continues through the present. Like the SHO V6 and SHO V8, the Sigma was designed with help from Yamaha.