Ford's 2.0 VVT Zetec engine
The 170PS 2.0-litre Duratec ST engine has been developed from the standard 130PS 2.0-litre Ford Focus (Zetec-E) engine with several new features, including;
- New, high-flow aluminium cylinder head with larger inlet valves and higher lift intake and exhaust camshafts for higher peak rpm levels
- Continuously variable intake valve timing
- High compression, cast-aluminium pistons and forged steel connecting rods
- Dual mass flywheel
- New dual state intake (DSI) manifold, using long runners for low-end torque and shorter runners for higher peak power outputs
- Larger bore free-flowing stainless steel exhaust system, tuned for enhanced performance sound.
Duratec ST's new aluminium cylinder head features enlarged intake ports to increase its flow potential. It is fitted with larger intake valves (33.5 mm) to further Duratec ST's free-breathing character. Stiffer springs on both the intake and exhaust valves help to facilitate a higher red-line.
The Focus ST170 has an indicated red line of 7,200 rpm on the tachometer and rev-limiter intervention beginning at 7,350 rpm.
Fuel is delivered to the cylinders via an electronically controlled, high-output fuel pump. With precise electronic control of the fuel delivery to the injectors, no return fuel loop is required.
This fuel system contributes to ST170's Euro Stage IV emissions capability.
Variable valve timing technology gives Duratec ST combustion efficiency that eliminates the need for a close-coupled catalyst in the exhaust system. This enhances its flow characteristics and performance capabilities further.
Duratec's intake camshaft is equipped with an electro-mechanical control mechanism that allows the cam's maximum opening point, relative to crankshaft degrees, to be varied between 85 and 145 degrees after top dead centre.
Variability is calibrated according to engine speed, load and operating temperature. It is accomplished by changing oil pressure on either side of a piston in a helix between the cam and its drive pulley.
On cold start-up, VVT helps to provide a precise combustion calibration that facilitates quick light up of the under body exhaust catalyst before adjusting to a profile for high combustion efficiency. As a result, SVE could position the catalyst unit - incorporating premium metallic elements - approximately 900 mm away from the cylinder head face to give Duratec ST its free exhaust flow with reduced back pressure.
A second catalyst unit is located downstream in the exhaust.
The exhaust system is constructed entirely of stainless steel, tuned for its throaty performance sound. Its exhaust manifold, cleverly designed for package efficiency in the Focus engine bay, is created of equal-length tubular headers in a four-to-two-to-one configuration.
The design combines the first and fourth cylinder exhaust tubes and the second and third cylinder exhausts, respectively, before the resultant two pipes are combined into one to enter the catalyst. The exhaust pipe diameter is 65 mm.
Robust elements were incorporated in Duratec ST's top end to reflect the additional performance demands being placed on the engine. These include stronger, lightweight, cast aluminium pistons with larger, 20 mm wrist pins and robust, sinter-forged connecting rods.photo of pistons here