With so much on the line and even more to prove to consumers, General Motors has previewed its latest in fuel-saving technologies for the upcoming 2009 and 2010 model years. As is the case with other manufacturers, GM has chosen to go the most cost effective direct injection (DI) route to up EPA estimated mpg fuel ratings, decrease emission outputs, and maintain sufficient power in its future vehicle lineups. The highlight of GM's DI surge will be a pair of engines -- a 2.4L four-cylinder and 3.0L V-6 -- set to debut at next month's Detroit auto show under the hood of the 2010 Chevrolet Equinox.
Before we delve into GM's expanding lineup of DI powertrains, it's probably best to break down the technology. Direct-injected motors receive their fuel delivery directly into each cylinder where it first evaporates, cooling the hot compressed air-fuel mixture, which makes it less susceptible to knock and therefore more tolerant of a higher compression ratio. In regular port fuel-injected engines, the injection and evaporation happens in the intake runner, well before the mixture enters the combustion chamber. Generally speaking, the process yields less fuel consumption, equivalent power production and reduced emissions versus non-DI motors. It also allows for cleaner cold starts through an easier ignition.
In addition to boasting direct injection, both engines utilize variable valve timing on both the intake and exhaust cams to improve performance. The 2.4L four-banger makes 182 hp at 6700 rpm and 174 lb-ft at 4400 rpm and features a high-compression 11.4:1 ratio for optimal power. Dished pistons allow increased combustion efficiency, while application-specific injectors automatically modulate fuel flow. It's based on the existing 2.4-liter, but the block is now sand-cast to improve strength and withstand the higher in-cylinder pressures (the previous engine used a lost-foam casting method). Its bigger 3.0L V-6 brother (255-hp, 214 lb-ft) is based off the current 3.6L direct-injected unit in the Cadillac CTS and incorporates an isolated fuel injector system for quieter operation. Rubber isolators are used with the fuel rail to diminish vibration and noise as well.