Where's My MPG?

Trade-Offs Along the Path to Better Fuel Economy


  • 2008 Buick Enclave

    2008 Buick Enclave

    The 2008 Buick Enclave gets good fuel economy thanks to a six-speed transmission that, some say, is too reluctant to downshift. Is this the trade-off for improved gas mileage? | March 18, 2010

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While on a family vacation, the head of Edmunds.com's testing department was pleasantly surprised by the high fuel economy delivered by the 2008 Buick Enclave CX he was driving. He was also surprised at how reluctant it was to downshift — and when it did kick down, it jumped from 6th gear to 4th.

"Clearly they had tuned it for fuel economy," said Dan Edmunds. "But I had to wonder if drivers were going to complain about the way you had to mash the gas pedal to get it to perform."

The Automotive Holy Trinity This was a good example of an automaker trading fuel economy — which everyone wants these days — for performance. Edmunds concluded that there was actually one more side to this issue, which he came to think of as "the holy trinity of fuel economy, performance and safety." Attempts to improve any one of these three things will bring a drop-off in one of the other two.

With this question in mind, we surveyed the automotive landscape to see how the seismic shift toward fuel economy is remapping the way cars are made. We found that, behind the scenes, engineers, designers and even marketers are changing the way cars are conceptualized, built and presented to the consumer.

Put another way, Detroit is hoping to disprove the old saying, "There's no replacement for displacement." What — if anything — will take the place of the big V8s that have thrilled American drivers over the past four decades? Or are we doomed to a future of creeping around in noisy, asthmatic econoboxes with four and (gasp) even three-bangers churning like hamsters on a treadmill?

An Embarrassing Situation The current situation was neatly described in the book Natural Capitalism by the famed environmentalist Amory Lovins (along with co-authors L. Hunter Lovins and Paul Hawken). They write that the contemporary car "after a century of engineering, is embarrassingly inefficient: for the energy in the fuel it consumes, at least 80 percent is lost, mainly in the engine's heat and exhaust, so that at most only 20 percent is actually used to turn the wheels. Of the resulting force, 95 percent moves the car, while only 5 percent moves the driver, in proportion to their respective weights."

The solution, the authors write, lies in three areas: 1) Making the vehicle ultralight; 2) reducing aerodynamic drag and rolling resistance; and 3) introducing hybrid-electric propulsion systems.

Since the authors wrote those words that were published in 1999, hybrids have, in fact, gained increasing popularity among automakers. But the gasoline-only powertrain is not yet in danger of extinction. In fact, Detroit automakers are seeking to refine the conventional car with some unconventional methods.

GM's Changing Philosophy

The Enclave mentioned in the opening was released by General Motors well before the big rise in gas prices in the spring of 2008. It is a good example of positioning a vehicle before market shifts and declining sales force a change.

Interestingly, GM power plants, such as the 6.2-liter V8 in the 2008 Chevrolet Corvette can also deliver respectable gas mileage, up to 26 mpg on the highway with a stick shift.

Sam Winegarden, GM's executive director of engine engineering, said GM designers are solving the problem by "virtually working it from the entire vehicle perspective." He mentioned improved aerodynamics, reducing weight by the use of premium materials and producing the lowest rolling resistance. He emphatically added, "We want to give the customer the best fuel economy and not sacrifice performance."

When it comes to the powertrain side of the equation, "we need to make a big engine look small," Winegarden said. This means that a V8 is designed with what GM calls "active fuel management" which, depending on load, will run on four of its eight cylinders, such as in the 2007 Chevrolet Tahoe we used for a fuel economy test.

Besides these innovations, Winegarden said GM is planning to increase its "hybrid portfolio" and to look to its overseas fleet for new diesel technology. He pointed to the tuning of the current Cobalt to produce the XFE model that gets 36 mpg highway, calling it the "playing out of some advanced technology functions." Another example is the downsized direct injection used in the Chevrolet HHR SS. "It has pretty awesome performance with good fuel," he said.

Ford Looks for a Boost

Meanwhile, Ford is revamping its lineup to meet fuel economy challenges without losing performance. According to Dan Kapp, director of powertrain research and advanced engineering, performance had always trumped fuel economy. But "with the extreme focus on improving fuel economy, it still isn't clear to us if with customers' demand for fuel-efficiency, they are willing to trade performance."

Enter Ford's new vehicle design philosophy called EcoBoost. EcoBoost's combination of turbocharging and direct fuel injection (injecting gas directly into the combustion chamber rather than into the intake manifold) offers the ability for a "downsizing stair step." Big V8s would be replaced by V6s which would, in turn, be replaced by four-cylinder engines.

"The beauty of [EcoBoost] is the technology gives a fantastic torque curve," Kapp said. He predicted a 10-20 percent increase in fuel economy and a driving dynamic (low-end torque) that drivers will love. "As the old saying goes, 'People buy horsepower but they drive torque.'"

Ford's new technology will debut in the 2009 Lincoln MKS followed by the Ford Flex.

A Ford spokesman said the 2009 Escape is another good example of increased attention to all the elements that make up improved fuel economy. The Escape received a larger four-cylinder engine for 2009, up from 2.3 liters to 2.5, delivering increased horsepower and performance, yet improved fuel economy by 2 mpg in highway driving. The 2009 model also has a six-speed transmission and is quicker than the 2008 model's V6 version with a four-speed transmission.

Weight Kills Fuel Economy

While GM and Ford explore new fuel-saving strategies, virtually every manufacturer is looking for ways to put all its vehicles on a diet. Mazda, Nissan and Toyota are all cutting weight in their fleets. BMW is finding that direct injection and turbocharging are ways to improve the performance of cars that many consider heavy, while still providing the legendary German performance.

While many people think of Honda as already being a leader in fuel-efficiency, that company is also aggressively counting calories — or at least ounces. Everything is being scrutinized, including the size of the welds on the door of the redesigned 2009 Honda Fit.

Weight was definitely on the mind of Craig Brazeau at Honda Research & Development, as the lead engineer on the 2009 Pilot. Still, the Pilot's vital statistics were improved: Fuel economy rose by 8 percent while horsepower was improved along with torque, safety and overall utility.

"All other factors being equal, the laws of physics dictate that the larger and heavier a vehicle, the more energy [fuel] it will take to move it," Brazeau said. "However, if you compare the fuel economy of today's midsize SUV and [crossover] offerings to similar vehicles available just five years ago, you will find that noticeable improvements have been made, and the current fuel economy levels are quite good."

What About Safety?

Ask an auto executive how safe the company's cars are and the answer is fairly predictable. For example, GM's Winegarden said, "The secret is that you have to make the vehicle crush safely in a crash. You can get some outstanding safety performance without having a lot of mass into the vehicle."

But Russ Rader, spokesman for the Insurance Institute for Highway Safety, provided an important wake-up call on this subject.

"Consumers tend to think of safety in terms of features like how many airbags you have," Rader said. "But the reality is that a smaller car is less safe in a crash with a larger car."

The reason becomes clear when you consider this example. If a 2,000-pound car runs head-on into a 4,000-pound car and both are going the same speed, the lighter car will immediately be accelerated backward and the heavier car will continue forward in the same direction.

"Small cars are much safer than they used to be," Rader said. "If you want to buy a small car, buy one with the best crash test. And make sure it has the latest safety features. The next frontier will be preventing crashes in the first place."

The Last Word

One thing is clear: Designers and engineers are entering a new age, a time when more will have to be done with less. And the result will even have to cost less, too. What is the magic solution to all of this? Imaginative design and sophisticated engineering.

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