While there is no special higher-mileage model of Dodge’s all-new, vastly improved 2009 Ram, Chrysler says its engineers “pulled out all the stops to offer customers significantly better fuel economy.” Among many other things, they substantially reduced aerodynamic drag, went to lower-rolling resistance tires, improved the efficiency of the transmission torque converter, and added variable valve timing to the available 5.7-liter Hemi V-8 engine, which already had Chrysler’s cylinder-deactivating Multi Displacement System. All this achieved an average 1-mpg improvement over 2008 models, making the new Rams roughly equal in efficiency to comparable non-XFE/SFE GM and Ford trucks.
Interestingly, all three domestic makers boast “best-in-class” aero drag, probably because different body configurations tested in different wind tunnels produce results that are not directly comparable one with another. Chrysler says its Ram Crew Cab 4x4’s Cd is 0.419, GM says its Silverado/Sierra XFEs tests at 0.412, and Ford says its SuperCrew 4x2 comes in at 0.403. Those numbers are all very close, and buyers should know that shorter cabs, longer boxes, add-on boxes, and even bigger mirrors will increase drag and reduce fuel economy.
The North American market’s two other full-size-truck competitors, Toyota and Nissan, have trailed the U.S. makers in this area but are working hard to compete. “We have the same options available to us as GM and Ford,” says Toyota’s Yerace. “One of the key things to look at is engine downspeeding. For a given speed, say 65 mph, maybe the engine is turning 2000 rpm. By changing to a lower numerical final drive, maybe now we can go down the road at 65 mph at 1800 rpm. You’ll notice it more on the highway than in the city, and you will lose some passing performance and some 0-to-60.”
Yerace also offers a pair of mass-versus-efficiency rules of thumb: “A 50-pound weight reduction is worth about one percent in fuel economy. Or, if you can reduce the mass by 10 percent, that’s worth about a 3.5 percent improvement. But certain vehicles lend themselves better to weight reduction than others, and it gets really difficult on a truck. The reason people buy trucks is for their capabilities. The last thing you want to do is make a truck get better fuel economy but lose its ability to do the job. You’ll lose a lot of customers if you do that. The real challenge is to maintain capability and get better fuel economy.”
Shunichi Inamijima, director of powertrain engineering for Nissan North America, says Nissan’s Titan pickups got a number of efficiency improvements when they were updated for 2007. Among those on the engine were continuously variable valve timing and such friction-reducing measures as piston ring coating and camshaft microfinishing, as well as some transmission tuning. He says the addition of CVTC alone is worth about 0.3 mpg.
Mr. Inamijima also has rules of thumb: Reducing a truck’s aerodynamic drag by 10 percent, he says, can improve its fuel economy by 1.5-2.0 percent, or about 0.45 mpg. Reducing its weight by 100 kilograms (220 pounds) can boost economy by about 1.5 percent, or 0.3-0.4 mpg. Reducing rolling resistance by 10 percent can get you 0.2-0.3 percent better economy. “But a 10-percent drag reduction is almost nonachievable,” he adds. “That is drastically changing the style of the body. In the real world, two or three percent is really tough for us. And 100 kilograms of weight is almost a hopeless number. That is almost downsizing the truck, which is really tough. Honestly, 1 mpg is a huge number for me.”