While some automakers have made a move toward smaller, turbocharged engines to improve fuel economy in cars like the Chevrolet Cruze and Ford Fusion, a new Consumer Reports study finds that these types of engines miss the mark in real world tests.

“We put the cars through our standard fuel economy tests, with both city driving and highway speeds,” says Tom Mutchler, Automotive Engineer at Consumer Reports. Among affordable midsize cars, the Ford Fusion with the turbocharged 1.6-liter EcoBoost engine got 25 mpg in Consumer Reports testing, while cars with larger, conventional four-cylinder engines like the Nissan Altima and Honda Accord delivered 31 and 30 mpg, respectively. Mutchler says that the Altima and Accord “are also quicker and have smoother power delivery than the Fusion.” The Altima and Accord matched their combined fuel economy ratings from the EPA in Consumer Reports’ tests, but the Fusion fell short of the EPA’s 29 mpg estimate.

The trend carries over to affordable compact SUVs as well. Despite similar fuel economy ratings of 26 mpg combined from the EPA, Consumer Reports found that the naturally-aspirated Honda CR-V accelerated more quickly and delivered better fuel economy than the Ford Escape with the 1.6-liter EcoBoost engine. The CR-V averaged 23 mpg in Consumer Reports tests, while the Ford Escape delivered 22 mpg. In the affordable small car class, Consumer Reports notes that the turbocharged Chevrolet Cruze Eco came in lower than its combined EPA rating of 31 mpg, earning 27 mpg in the publication’s study.

While this isn’t the first time Consumer Reports has called fuel economy into question, some members of the automotive press are unsurprised by the test results. “Turbocharged and naturally aspirated engines vary little in combustion efficiency, so both powertrains require about the same amount of fuel to produce the same number of ponies,” writes Popular Mechanics. “As a result, bolting on a turbo to a slightly smaller engine doesn't instantly translate into better performance; it just lets the driver tap into an extra boost at higher RPM's.”

Consumer Reports’ tests come at a time when Americans are spending more of their pretax income on fuel than they have in the last 30 years. The U.S. Energy Information Administration reports that four percent of the average household's income was spent on gasoline in 2012, which equates to $2,912.

If you’re shopping for a new car, Mutchler says that “what’s important are the actual fuel economy numbers, not necessarily the size of the engine under the hood.”

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