The Ford Sigma is a small straight four 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 SHO V6 engine, development of the Zetec-S was a collaborative effort between Ford, Mazda and Yamaha. The engine's sound profile was refined in Ford's 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 debuted in 1995, it included many firsts, including 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 at the time. This feature 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 is done with a conventional cylinder block — the entire assembly has to be renewed. Despite this, 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 1242 cc capacity, with 1388 cc, 1596 cc and 1679 cc 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 1679 cc 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 155 PS 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 cheaper version of the Zetec-SE engine, to compete with the classic Volkswagen EA827 engine series known locally as Volkswagen AP (from Alta Performance, "High Performance" in English) engine in Brazil. It is 8v SOHC instead of 16v DOHC and its block is made of cast iron instead of aluminum. Also, its camshaft is driven by a chain instead of a belt. As a result this engine exhibits rougher behaviour, producing more vibration and noise. On the other hand, it has a superb torque output thanks to the addition of the RoCam (Rollifinger Camshaft) feature. It's also a much smaller engine than the SE version, which allowed it to be installed on the Ford Ka, replacing the Endura-E engine which by that time was considered underpowered and outdated. The engine also featured a new patented process for the aluminum head production, which resulted in a better alloy than those produced in Spain and UK, and at a lower production cost. In 2002 a supercharged 1.0-litre 95 PS version was released for the Ford Fiesta, to compete with the 1.0 Turbo 16v 112 PS version of the Volkswagen Gol. In 2001 the Zetec RoCam engine was introduced in Europe, but labeled as Duratec 8v, for the Ka and Fiesta. Later a 1.6-litre version was also released for the SportKa and StreetKa. The European versions of the engine are produced in the South Africa plant. In October/2004 a newer bi-fuel version was introduced labeled "1.6 L Flex", capable of running on both petrol and ethanol, even mixed at any proportion. This version also featured a high compression ratio of 12.3:1 and "Compound High Turbulence" chambers, as used on the CHT engine. The 1.0 L Flex runs with a compression of 12.8:1. Currently, this engine powers nearly all Brazilian Ford models – except those with 2.0 litre engines – in many different variants:

Applications

1596 or applications:

Duratec

After an upgrade to the Sigma, Ford renamed it the Duratec.

Duratec Ti-VCT

The 1596 cc Ti-VCT (Twin independent Variable Camshaft Timing) version includes variable valve timing, and generates more power and torque than non-VVT counterparts. Latest versions comply with the Euro5 emission level.

Crate engine versions

Crate engine versions of Zetec-SE engines are sold by Ford Power Products under the name ZSG Range.

Applications

Current use

The Ford Sigma engine was produced at Bridgend Ford in Wales, U.K. until September 2020 and at Taubate Engine and Transmission Plant, Taubate, São Paulo, Brazil. Today the Sigma engine is used as the basis for the four cylinder Ford Ecoboost 1.5 litre and 1.6 litre engines. A 110 bhp version was used by Morgan for their 4/4 Roadster coupled to a Mazda transmission from 2009 until the model was discontinued in 2018.

1.25/1.4/1.6 L Sigma

These engines in the first generation Focus produced 75 and 100 bhp respectively, but for MkII Focus the 1.4 variant was slightly modified and produced 80 bhp. Both engines have belt driven camshafts and Electronic Fuel Injection systems. They weigh 90 kg. The 1.6 Ti-VCT was introduced in 2004, it features Variable Cam Timing; this 115 bhp version is used in MkII Focus. A new 105 bhp or 125 bhp EU5 version is used in the MkIII Focus, also a 1.6 L 120 hp version is used in Ford Fiesta Zetec-S. The Sigma is usually coupled to the Ford IB5 five-speed manual transmission.

Brazil

Recently the Sigma engine was present in modern Brazilian versions of the Fiesta, Focus and Ecosport (1.6 L TI-VCT version) and a 1.5 version was used by Ka. This engine was able to use the flex technology. Power with ethanol:

Caterham usage

Some Caterham Cars use modified Ford Sigma engines such as the Caterham Seven 270, which uses a tuned Sigma engine producing 135 hp at 6,800 rpm as a modern equivalent to the original Ford Kent Crossflow engine used in the Lotus 7 from 1957 to 1972. Ford Sigma 1.6-litre overview Technical features:

SCCA Spec Racer

The third generation of the SCCA Spec Racer, commonly known as the Gen3 was introduced in 2015, and uses the 1.6 L Sigma engine. The engine is sold by SCCA Enterprises as a sealed unit.

Zetec-E comparison

The Zetec-SE has no common parts or design with the larger Zetec-E engines apart from the name. This gives rise to some confusion since it suggests that they are members of the same family when they are, in fact, completely different. Zetec-E units are mounted transversely with the inlet manifold at the rear, whereas the Zetec-SE units are mounted with the inlet manifold at the front.

Replacement

In 2012 Ford replaced the Sigma engine with a brand new 3-cylinder 1.0-litre EcoBoost engine for some markets and models. The new engine provides more power and torque with less fuel consumption and lower Carbon dioxide emissions.