The Ford Sigma is a small straight-4 automobile engine introduced in 1995 by Ford Motor Company. Its first evolution was sold as the Zetec-S (not to be confused with the trim level), then Zetec-SE and finally, in later years, renamed Duratec. The last upgrade of the engine is named Duratec Ti-VCT. Conceived for Ford's smaller models, the motor was intended to replace the older HCS (a derivative of the even older Kent unit) and smaller capacity CVH units. Introduction and production As with the Ford Taurus SHO's SHO V6 engine, development of the Zetec-S was a collaborative effort between Ford, Mazda and Yamaha. The engine's sounds were refined in the Ford acoustics center in Cologne-Merkenich, Germany. Production of the Zetec-SE was carried out in the Ford Valencia Engine Plant, with Yamaha building the 1.7 L engine blocks in Japan. When the Zetec-SE first arrived in 1995, it included many firsts, such as a plastic inlet manifold, a "ladder" style main bearing and crankcase assembly, and big-end bearing caps which are forged in one piece and subsequently split. It also incorporates powder metal connecting rods, which were quite exotic and notable at the time. This feature however makes the engine more challenging to rebuild at the end of its working life, since it is not possible to re-machine the bearing ladder as would be the case with a conventional cylinder block - the entire assembly has to be renewed. Despite this however, engine tuners have found novel ways to increase the power of the unit through use of different valves and increasing the compression ratio of the engine through skimming of the cylinder head. The engine first appeared in the Mk4 Ford Fiesta and the virtually identical Mazda 121 in capacity, with , and derivatives coming later. Difference between Zetec-SE/Zetec-S/Duratec/Duratec Ti-VCT The Sigma engine was introduced under the Zetec-S name; after the upgrade it was renamed to Zetec-SE, Duratec and Duratec Ti-VCT. The latest upgrade of Sigma is called Ecoboost 1.6 engine (Not to be confused with the smaller 1.0 or larger 2.0/2.3 engines) Zetec-S/SE Zetec-S The engines uses a heavily modified 1.4 L engine block and features Variable Cam Timing on the inlet camshaft. This displacement has only been used in the Ford Puma. A version of this engine was developed for the Ford Racing Puma with only 500 units built. Zetec RoCam In 2000, Ford of Brazil developed a