GM has introduced its 2007 model year full-size SUVs, redesigned, based on a new GM full-size platform, and offering new powertrains that deliver incremental improvements in fuel economy through technologies such as displacement on demand and new transmissions. It is on this new platform that GM has pledged first to introduce its two-mode hybrid system.
Yet as critical as the full-size SUVs are for GM’s financial picture, the company is stating up front that they expect flat sales in the segment—i.e., no growth.
Flat sales seems a lot to ask for. Despite extensive discounting, sales of GM’s full-size SUVs dropped 23% in August year-on-year. Ford is doing worse—sales of the Expedition dropped 40.2% in August year-on-year.
GM is leading the rollout with the Chevy Tahoe, the best-selling full-size SUV. (August sales dropped 33.9% from 15,051 in 2004 to 9,994 this year.)
This new generation uses the Gen IV small-block V-8 engine family, with displacements ranging from 4.8 liters to 6.2 liters, and horsepower ranging from 290 hp (216 kW) to 400 hp (298 kW).
Variable Valve timing is used on some engines to enhance performance and efficiency, as is Displacement on Demand.
|Engine Offerings for the GM 2007 Full-Size SUVs|
|4.8 L||iron||RPO LY2||290 hp (216 kW)||–|
|5.3 L||iron||RPO LY5||320 hp (238 kW)||Displacement on Demand|
Includes E-85 version (RPO LMG)
|5.3 L||aluminum||RPO LC9||320 hp (238 kW)||Displacement on Demand|
|6.0 L||iron||LY6||350 hp (260 kW)||Variable Valve Timing|
|6.0 L||aluminum||L76||355 hp (264 kW)||Displacement on Demand|
Variable Valve Timing
|6.2 L||aluminum||L92||380 and 400 hp
(283 and 298 kW)
|Variable Valve Timing|
The two 5.3-liter engines that are E85-compatible use a new virtual fuel sensor. The Engine Control Module (ECM) samples the exhaust at the oxygen sensor, and an algorithm determines whether E85 is used, as well as its mixture percentage with gasoline. This, according to GM, is a much simpler, less costly system than previous systems that relied on fuel composition sensors. In fact, the entire system on the engine is simple: only the fuel rail and fuel injectors are different between E85 versions and non-E85 versions.
(If you ever wondered about the predilection of automakers to build millions of flex-fuel vehicles prior to widespread demand or the existence of a pervasive E85 fueling infrastructure: federal regulations allow automakers to use flex-fuel vehicles for CAFE mileage credits (and EPAct conformance)—whether the driver actually ever uses E85 or not.)
The 2007 Tahoe with the 5.3-liter engine delivers, according to GM’s early estimates, combined cycle fuel economy of 20.5 mpg US (11.5 l/100km) in two-wheel drive, and 20.1 mpg US in 4-wheel drive. That’s a big relative increase from the 2005 Tahoe’s (5.3-liter, 2WD) combined results of 17 mpg US—but still falls well below even the current CAFE standard target for 2007 of 22.2 mpg.