The Saturn Sky Red Line has a two liter turbocharged Ecotec engine that generates 260 hp and 260 lb.-ft. (353 Nm) of torque. This high performance engine from General Motors features gasoline direct injection and variable valve timing. Its twin-scroll turbocharger also has an air-to-air intercooling system.
According to Green Car Congress, the newly announced 3.6L VVT V-6 is GM’s third engine with gasoline direct injection following:
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The introduction of GM Powertrain’s Ecotec 2.0-liter four-cylinder Turbo engine with direct injection on the 2007 Saturn Sky Red Line and Pontiac Solstice GXP roadsters.
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GM has been delivering a naturally-aspirated Ecotec 2.2-liter direct injection engine on Opel models in Europe since 2004.
There then ensued a debate by GCC readers over the direction taken by the development. In response to the report that direct injection “reduces fuel consumption by up to 3% while increasing power by 15%.” The first commenter to the article complained:
That’s the problem right there. Instead of putting efficiency gains into downsizing and fuel economy, they put them into yet more useless power.
Which prompted another commenter to come to GM’s defense, “The good news is that they got on board with DI at all.” To which, a third observes:
This is a step in the right direction, but yet again, GM is still doing it the “old way”. By that I mean that they must not be using the latest DI technology. If they were, the fuel efficiency gains would be closer to 10% without downsizing. That is primarily accomplished through running a lean mixture. I know that presents new emissions issues, so maybe GM can’t figure that out. Yet again, must be using the technology of 5 years ago!
The 3.6-liter VVT DI is a version of GM’s 3.6-liter V-6 gasoline engine with the addition of direct injection and variable valve timing. The power plant should appear in a 2008 model and “GM projects that by 2010 one out of every six GM vehicles in North America will be equipped with a direct injection engine.” Says Tim Cyrus, GM’s chief engineer responsible for the development of Northstar V-8 engines and other V-6 with special features, “The 3.6-liter VVT with direct injection will be our highest specific output, non-turbocharged V-6 engine, as well as one of the most fuel-efficient offerings in our high-feature family.”
This observation prompted debate over GM’s failure to produce a car for the American market that provides 40 MPG.
The GCC article provided extensive technical detail about the advantages of this technology:
Direct injection delivers precisely metered fuel directly to the combustion chamber, producing a cooling effect in the chamber. Cooling the incoming air charge enables a higher compression ratio (greater than 11.0:1 in the case of the 3.6), which also improves engine efficiency. Less fuel is required to produce the equivalent horsepower of a conventional port injection combustion system.
The fuel injectors in the gasoline direct injection system are located beneath the intake ports. The intake ports only transfer air, unlike port fuel injection, which flows air and fuel, thus increasing efficiency.
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 1,740 psi (120 bar) of pressure.
The system regulates lower fuel pressure at idle—approximately 508 psi (35 bar) and higher pressure at wide-open throttle. The exhaust cam-driven high-pressure pump works in conjunction with a conventional fuel tank-mounted supply pump.
The 3.6-liter VVT DI is based on GM Powertrain’s 60-degree dual-overhead cam (DOHC) V-6 engine. The 3.6-liter V-6 VVT DI employs four-cam phasing to change the timing of valve operation as operating conditions such as rpm and engine load vary.
The result is linear delivery of torque, with near-peak levels over a broad rpm range, and high specific output (maximum horsepower per liter of displacement) without sacrificing overall engine response and driveability.
Cam phasing also reduces exhaust emissions by optimizing exhaust valve overlap and eliminating the need for a separate exhaust gas recirculation (EGR) system.
By closing the exhaust valves late at appropriate times, the cam phasers allow the engine to draw the desired amount of exhaust gas back into the combustion chamber, reducing unburned hydrocarbon emissions.
The return of exhaust gases also decreases peak temperatures, which contributes to the reduction of oxides of nitrogen (NOx) emissions. In tandem with the 25% reduction in cold-start hydrocarbon emissions brought on by direct injection, the 3.6-liter VVT DI V-6 surpasses all emissions mandates, and does so without complex, weight-increasing emissions control systems such as EGR and air injection reaction (AIR).
That such direct injection technolgy achieves a 25% reduction in cold start hydrocarbon emissions, prompted one pundit to observe: “Tailor-made for a hybrid.”
