Direct Injection
Perhaps the most innovative feature of the new turbocharged Solstice powerplant is the direct injection system. Essentially, the system locates the injector in the combustion chamber rather than in the intake manifold runner or intake port. This arrangement is similar in layout to a diesel powerplant, exposing the injector to the heat and pressure of the combustion event. Unlike a diesel, the Ecotec uses a conventional spark plug and otherwise operates as a normal four-cycle spark-ignition engine. The system is referred to as Spark Ignition Direct Injection (SIDI).
With fuel delivered directly to the combustion chamber to create a more complete burn of the air/fuel mixture, less fuel is required to produce the equivalent horsepower compared to a conventional port-injection system, particularly at normal cruising speeds. "Direct-injection technology works well with turbocharging and helps deliver a great balance of power and economy," says Groff. "The Ecotec 2.0-liter Turbo produces the power expected of a V-6, but in a smaller, more efficient package--and the driving response is simply terrific."
To accommodate the direct-injection system, the Ecotec 2.0-liter Turbo has a unique cylinder head and intake manifold. The cylinder head incorporates mounting locations for the fuel injectors--which are typically mounted in the intake ports or intake manifold on port injection engines. A high-pressure fuel pump delivers fuel to a variable-pressure fuel rail. Fuel enters the combustion chamber through multihole fuel injectors. The fuel pump, fuel-rail pressure, fuel-injection timing, and injection duration are controlled by the engine control module. In this way, fuel is metered and delivered in a finely atomized spray, which, during the intake stroke, is introduced into the chamber near the intake valves, in direct line of the spark plug. SIDI also permits a slightly higher compression ratio than if the fuel were delivered with conventional fuel injection and allows the mixture to be leaner at full power.
 Solstice's interior is attractive,...  Solstice's interior is attractive, and the gauge cluster is large and easy to read. |  A short shifter handle operates...  A short shifter handle operates the Aisin five-speed manual transmission. |  The rear of the Solstice GXP...  The rear of the Solstice GXP shows the crisp, sporty lines that have captured the interest of the import-car-buying market. Dual headrests recall sports racers past and present. |
A high-pressure, returnless fuel system is employed for this application. It features a high-strength stainless steel fuel line that feeds a variable-pressure fuel rail. Direct injection requires higher fuel pressure than conventional fuel injected engines, and an engine-driven high-pressure fuel pump is used to supply up to 2,250 psi of pressure. This system regulates lower fuel pressure at idle--approximately 752 psi and higher pressure at wide-open throttle. The cam-driven, high-pressure pump works in conjunction with a conventional fuel tank-mounted supply pump.
Apart from the mounting positions of the fuel injectors, the cylinder head has conventional port and combustion chamber designs, although both are optimized for direct injection and high boost pressures. Sodium-filled exhaust valves and stainless steel exhaust manifold are durable components designed to stand up to the high-performance capability of the engine.
A unique cylinder head, fuel system, pistons, intake manifold, and the dual-scroll turbocharger are the only major components that differentiate the 2.0-liter Turbo from other members of the Ecotec engine family. Mobil 1 synthetic engine oil is added at the factory. Synthetic oil was selected for its friction-reducing capabilities and high-temperature performance.
Dual Cam Phasing
The camshafts of the Ecotec 2.0-liter Turbo engine have phasers that support the continu-ously variable intake and exhaust valve timing. They also have cam position sensors, so that the engine control module can accurately control valve timing. The crankshaft and camshaft position sensors are digital. A new engine controller, specific to this powerplant, is used to sense and dictate its performance parameters.
Variable intake and exhaust timing works synergistically with both the gasoline direct injection and turbocharging systems. The variable engine timing enabled by cam phasing allows the combustion process to be optimized. Also, valve "overlap" at low rpm can be adjusted by the controller to increase the response of the turbocharger, providing a more immediate feeling of power.