The 3.6 L V-6 on the 2008 STS is General Motors' first V-6 gasoline engine with direct injection. Combined with other powertrain changes including variable valve timing, the fuel economy of the STS improves by 1 mpg in the city and 3 mpg on the highway.
Initially offered as the top-level engine in the new 2008 Cadillac CTS, the engine delivers 304 horsepower (227 kW) and 273 lb.-ft. of torque (370 Nm) — a 15% increase in horsepower and 8% increase in torque. In addition to a 3% improvement in brake-specific fuel consumption (BSFC), the V-6 achieves approximately a 25% reduction in cold-start hydrocarbon emissions.
The direct-injection engine was named to Ward's AutoWorld magazine's 2008 “Ten Best Engines” list for North America and the 3.6 L V-6 VVT with direct injection in the 2008 Cadillac CTS was named Motor Trend's 2008 Car of the Year.
In gasoline direct injection (GDI), the injectors must operate at high pressures, so higher voltages are used to provide quicker response than conventional fuel-injection systems. In the 3.6 L V-6, an engine-driven high-pressure fuel pump supplies fuel at pressures up to 1,740 psi (120 bar). While the higher pressures are required at wide-open throttle, at idle the system regulates the pressure to approximately 508 psi (35 bar). The exhaust cam-driven high-pressure pump supplements the tank-mounted fuel pump.
By spraying fuel directly into the engine cylinder, a cooler air-fuel mixture results allowing the use of a higher compression ratio of 11.3:1 for improved engine performance and efficiency.
For cold starting, direct injection can create a richer air/fuel mixture around the spark plug to improve ignition. Besides smoother operation, this results in a reduction of approximately 25% in cold-start hydrocarbon emissions during the cold start and warm up.
To reduce the overall engine noise, the 3.6-liter V-6 also incorporates the U.S. automotive industry's first isolated fuel-injector system.
OTHER POWERTRAIN ADVANCEMENTS
In the direct-injected V-6 engine, variable valve timing helps reduce exhaust emissions and improve performance and fuel economy. VVT optimizes the phasing of the intake and exhaust valves relative to the crankshaft position at all operating conditions. This produces a linear delivery of torque, with near-peak levels over a broad rpm range, and high specific output (maximum horsepower per liter of displacement) without compromising overall engine response and driveability.
In addition to direct injection and variable valve timing, electronic features found on the 3.6-liter VVT DI include electronic throttle control with integrated cruise control, coil-on-plug ignition and an advanced direct-injection-capable engine control module (ECM).
While the 3.6 L V-6 engine is GM's first V-6 with direct-injection technology it is the third gasoline engine offered with the technology. Direct injection is among the key technologies to taking homogeneous charge compression ignition (HCCI) combustion technology out of the laboratory. Late in the fall of 2007, GM demonstrated two modified four-cylinder engines with HCCI that built on the company's expertise in gasoline direct-injection and variable valve actuation technologies.
DIRECT TO THE FUTURE
By the end of 2008, GM says it will produce as many as 200,000 vehicles globally with direct-injection technology. Further out, by 2010, GM projects one of every six of its North American vehicles will be equipped with a direct-injection engine.