The 2.0 litre ECOTEC 16-valve turbocharged engine delivers peak power of 147kW @ 5600rpm. The torque curve rises steeply from almost any idle speed and reaches its peak of 250Nm at 1950rpm (PULP) and a constant boost pressure of 0.85 bar, or 12.33 psi. The torque curve remains virtually flat with maximum pulling power available up to 5600rpm.
The electronic engine management system makes additional power available for acceleration at full load, allowing the engine cut-off speed of 6400rpm to be exceeded by 400rpm for short periods to ensure ideal transitions between gears.
The engine is a model of efficient packaging; all the components specific to the turbocharger have been accommodated without modification to the body or engine compartment.
The K04 Turbocharger unit incorporates friction-type bearings. The minimum/maximum revolution speeds are 5000rpm and 164,000rpm respectively.
In the integral turbocharger system, the exhaust manifold and turbine casing are combined into a single module with other components.
Advantages include compact dimensions and low weight; the casing weighs 4.3kg and the entire module weighs 7.1kg, which is about 1.3kg heavier than the cast manifold of the comparable naturally aspirated engine. Other advantages are its uniform wall thickness, which allows the engine to react quickly to temperature changes in the exhaust system, the reduced number of components and the elimination of a seal between the turbocharger casing and the turbine.
The basic engine dimensions are notable for a precisely square bore/stroke ratio of 86.0/86.0mm, cylinder spacing of 93mm and a compression ratio of 8.8:1.
The splash-lubricated pistons are manufactured from an aluminium/silicon alloy to ensure rapid heat dissipation and high mechanical strength.
Piston design also takes acoustic optimisation into account. The centre lines of the floating piston rings, for example, are offset by 0.8mm towards the pressure side of the piston. Two counter-rotating balance shafts ensure smooth, quiet operation. The four valves per cylinder have sodium-cooled exhaust valves and are driven directly via hydraulic bucket tappets from two camshafts with sporty cam profiles.
The turbocharger is connected to the engine’s lubricating and cooling circuits by separate feed lines. An oil cooler ensures thermal stability in the engine and its auxiliaries. A charge-air intercooler increases the amount of air entering the engine, promoting efficiency and torque development. A latest-generation computer system is responsible for overall engine management. Among other things, it controls the boost pressure using integrated relief and rotary valves.
The electronic ‘drive by wire’ accelerator, hot-film air mass meter, sequential fuel injection, individual-coil direct ignition and cylinder-selective knock control are all co-ordinated by the electronic management system.
On the road, the integrated turbocharger is notable for its spontaneous response to accelerator movements and its flexibility, even at low engine speeds. Short flow paths between the engine exhaust duct and the turbine and the low inertia of the compact turbocharger promote plenty of low-end torque.
Pollutants are substantially reduced by a double catalytic converter system comprised of a primary converter close to the engine, which comes on line quickly, and a large-volume main converter.
To achieve the maximum conversion rate, metal instead of ceramic material is used for the substrate that supports the catalytic precious metal coating. Two oxygen sensors monitor the combustion process: one is upstream of the primary converter and controls the composition of the fuel/air mixture, while the second, downstream of the main converter, is used for diagnostic purposes. This advanced concept allows Astra Turbo models to meet the Euro 4 emissions standard that comes into force in 2005 in Europe.
Engine validation testing involved a number of special test programs, including extreme altitude, winter and summer tests. As an example, in thermal shock tests, engine coolant was chilled to minus 25° C and within a few seconds the engine was subjected to full load.
Additional Australian testing of prototype vehicles and engines included powertrain suitability of the Z20LET and correct operation of engine management systems, calibrations and transmissions in hot ambient temperatures.
Existing hot test data, including Opel test results, were analysed to determine regional audit requirements.
Resulting engine calibration testing included purge operation, knock control, hot start and hot fuel handling and hot vehicle performance.
Manual transmission operation, oil temperature testing, and HVAC performance and cooling validation was carried out. In addition, vehicle durability testing confirmed the vehicles met Australian requirements