Opel GT: In Depth

Plenty Of Power In All Situations Thanks To High-Tech Engine

Innovative features include direct injection, camshaft phasing and turbocharging
Classic configuration: Twin A-arm and perfect weight distribution

No other Opel engine has ever produced 132 hp output per liter. The new Opel GT’s engine is the perfect complement to the car’s dynamic look. The 1998 cm³, four-cylinder all-aluminum engine also boasts impressive performance data compared with competitor engines thanks to high-tech features such as gasoline direct injection, twin-scroll turbocharger with intercooler, double camshaft phasing and two balance shafts. Maximum output of 194 kW/264 hp at 5300 rpm and high torque plateau of 353 Nm between 2500 and 5000 rpm ensure plenty of power in all situations. The roadster accelerates to 100 km/h from a standing start in just 5.7 seconds and reaches a top speed of around 230 km/h, which for a roadster is more of a notional value. It requires an average of 9.2 liters of super unleaded gasoline per 100 kilometers (MVEG-mix). Jointly developed by GM Powertrain engineers on both sides of the Atlantic, the ECOTEC engine is based on the 2.2-liter direct injection unit available in the Vectra model range since 2004, and on the 2.0-liter turbo induction unit, which debuted in the Vectra GTS in spring 2003.

Perfect combination: Direct injection and turbocharging

The Opel GT’s direct gasoline injection ensures considerably more intensive combustion of the fuel mixture than an induction injection engine. Driven by the camshaft, a
high-pressure gasoline pump increases fuel pressure to up to 155 bar ? when the engine is idling, injection pressure is 50 bar. The fuel itself is drawn from the tank by an electric pump. The multi-port injection nozzles are arranged underneath the four-cylinder’s intake ports. The special shape of the piston head causes the fuel mixture to swirl around the centrally located spark plug. Controlled and complete combustion allowed for the compression ratio to be set especially high for a high-performance turbo engine at 9.2:1, which is beneficial for consumption in the partial-load range.

The four-cylinder engine’s turbocharger operates according to the twin-scroll principle. In the exhaust manifold and turbocharger, the geometry of the first and fourth, as well as of the second and third cylinder channels keeps them separated from each other. The pulsating mixture columns are directed into scrolls and merge directly in front of the turbine. Separating the exhaust-gas streams until they reach the turbine inlet enables optimal use of their dynamics. Pressure already starts to build up at around 1400 rpm, and gas pedal movements are translated into powerful acceleration just as quickly. Maximum turbo pressure is 1.38 bar. Other important features of the extremely compact turbocharger include an electro-magnetic overrun air valve, vacuum control and a turbine rotor optimized for efficiency. At a defined vacuum pressure, a valve is opened which directs the air back to the compressor inlet, keeping the charger’s rpm at a high level. With renewed acceleration, turbo pressure is immediately available again. To increase charging efficiency in the combustion chambers, the pre-compressed air is cooled by 100 degrees Celsius in an intercooler before entering the combustion chambers.

Opel’s second-generation, reinforced aluminum engine block is used in the GT; in particular, the main crankshaft bearing supports and cylinder walls have been strengthened. The high-performance engine’s high thermal load capacity facilitates the piston end’s oil-spray cooling and backs up the cylinders’ wet liner, which extends far downwards. The cast aluminum pistons transfer power via forged piston rods to the forged crankshaft.

Clever double camshaft phasing

Both of the four-cylinder’s camshafts can be adjusted via an electro-hydraulic rotary disk to match valve opening times to the engine load level via the engine control unit. With higher overlap at lower rpm, continuous variable camshaft phasing also ensures that the turbocharger responds more quickly. The exhaust valves are filled with sodium, and exhaust gases are released to the tailpipe via a stainless steel manifold. All valves are operated via low-friction roller valve levers.

The engine block also features two counter-rotating balance shafts, a low-maintenance chain drive for the camshafts and a cast-on oil filter housing, which is easily accessible from above. Only the cartridge needs replacing when changing oil, and the appropriate time for this is indicated by an interval display. Sensors measure the usage rate of the fully synthetic oil based on parameters such as the number of cold engine starts and the ignition sparks produced by the spark plugs. The plugs themselves only need changing after 160,000 kilometers and the coolant after 240,000 kilometers.

Chassis with classic sporty configuration

For the Opel GT, engineers designed a classic, sporty configuration based on a rigid chassis, wide track (front/rear: 1543/1561 mm) and long wheelbase of 2415 mm: all four wheels are suspended from twin A-arms made from forged aluminum, the center of gravity is low, and the weight distribution of 51:49 percent (front/rear) is well balanced. A manual five-speed transmission with sporty, short gear travel and limited slip differential provide propulsion power. A torque beam between the transmission and rear axle suppresses reactions to acceleration/deceleration effects.

While disk brakes on all wheels, ABS, Traction Control (TC) and the Electronic Stability Program (ESP) monitor safety, the driver can control the level of ESP and use of TC himself. Both systems are fully active after ignition, with the setup providing driving fun but also keeping the vehicle stable within the physical limitations. At the touch of the ESP button in the instrument panel, the Traction Control (TC) is switched off, but ESP remains active and intervenes as soon as the yaw angle exceeds certain thresholds. Two short presses change the ESP’s calibration to a sportier mode and keep the Traction Control (TC) deactivated. Pushing and holding the ESP again for around ten seconds until the “ESP Off” symbol illuminates, completely deactivates ESP and TC. A short press of the button in any mode returns the two systems to their normal states, which also occurs automatically with each new engine start. A display and control light in the instrument panel keeps the driver informed about the current status of both systems.

Town, Country, Highway ?Tough Practice Test

Rolling hills and dense forests, picturesque castles, quaint half-timbered houses ? it’s not surprising that the idyllic Odenwald forest is one of the most popular places to visit in southern Hesse. However, the Opel development team members are less interested in tourist attractions and more in the varying demands of the roads when they test a new model to its limits along a standardized 200-kilometer course ? a rite of passage every new Opel model has had to pass for the last two years.

As with all Opel cars, the GT’s ambitious target was to cover 100,000 kilometers in only around 26 weeks. The average driver would take between four and seven years to travel the same distance. “During this long-term testing, we thoroughly evaluate the cars on a continuous basis from the viewpoint of our customers”, explains Michael M. Meyer, Manager, vehicle endurance and long-term quality. Two Opel GTs were in operation from 6:15 a.m. to 10 p.m., Monday to Friday, covering four circuits for a total of around 800 kilometers per day and car.

The GTs return to the Development Center between circuits, so that the specially trained drivers can give immediate feedback. At the end of the shift, the engineers analyze how the circuits went. “Because of the proximity to our Development Center, we have up-to-the-minute data,” says Meyer. “The varied nature of the course was also important.” Highway and country roads made up the majority of the circuit, each accounting for 40 percent of the course, while a four kilometer stretch was purposely driven on very poorly maintained roads. “One thing must be made very clear about this testing process: being a test driver has nothing to do with racing around. Safety and strict adherence to all traffic regulations and speed limits are an integral part of testing,” adds Meyer.

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Source: Source: Adam Opel AG