Report: To Keep Safety, Performance, MPG Gains Come At A Price

June 4, 2010
2011 Chevrolet Cruze

2011 Chevrolet Cruze

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If we want to keep our vehicles as safe as they are and don't want to sacrifice performance either, improving fuel economy will come at a substantial extra cost per vehicle.

That's the predictable conclusion made by a new National Academy of Sciences report released this week. The study had been requested by the National Highway Traffic Safety Administration (NHTSA) in 2007—well before the pending fuel economy rules were written—to objectively and independently assess the technologies that might improve fuel economy and find the incremental cost associated with them.

The panel, made up mostly of academics, broke down individual technologies that are being put into vehicles currently or in the near future and calculated how fuel consumption can be cut as a result.

What makes this report different is that along with the estimated gains of fuel efficiency for each technology, the panel also estimated the typical per-vehicle cost of each technology. And to help show that some technologies affect small vehicles differently than larger ones, it calculated the effects for in-line four-cylinder, V-6, and V-8 engines, respectively.

Including the typical markups of including new technologies, turbocharging and downsizing was calculated to cost the least for V-6 models—less than $50 from its preceding technology—while the estimate was a much harder-to-swallow $645 for already more price-sensitive four-cylinder models.

Some of the strategies were found to better benefit larger engines than smaller ones; for instance, turbocharging and downsizing was found to cut fuel consumption by an average of 3.5 percent for four-cylinder engines but five percent for either V-6 or V-8 engines. Combined with the extra cost for small engines, that might help provide some insight as to why more automakers haven't done what GM is doing with its 2010 Chevrolet Cruze. In the Cruze, a new turbocharged 1.4-liter four produces the effective power of a 2.0-liter or larger engine while allowing efficiency gains.

Advanced Diesel: High Cost, Big Improvement

2010 Volkswagen Jetta SportWagen

2010 Volkswagen Jetta SportWagen

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Conversion to diesel was estimated to cost nearly $3,600 for four-cylinder engines—a difference that we see reflected in the $5k price difference between the base 2010 Volkswagen Jetta and the Jetta TDI—and nearly $4,800 for V-6 engines. Advanced diesel racked up another $780 and $1,025, respectively, in additional cost. But the potential gains here are huge: Conversion to diesel would provide a 25-percent reduction in fuel economy, according to the panel, while a conversion on to advanced diesel would allow another ten percent.

The panel also laid out improvements for various types of hybrid technologies. For instance, a power-split hybrid system—such as that used in the 2010 Toyota Prius—reduces fuel consumption an average of 37 percent, while an integrated starter-generator (mild hybrid) system—such as what's used in the 2010 Honda Insight—reduces consumption by an average of 34 percent.

More ratios and improved internals for automatic transmissions could boost efficiency, but going to either dual-clutch transmissions or CVTs could provide the greatest gains (up to 7.5 percent, on average, from a six- or seven-speed dual-clutch gearbox like VW's DSG). Overall, the panel assesses, " Transmission technologies have improved significantly and, like other vehicle technologies, show a similar trend of diminishing returns."

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