Consumer Reports finds small turbo engines don't deliver on fuel economy claims
Feb 5, 2013 12:01 AM

Small turbocharged engines are marketed as delivering the power of a large engine, with the fuel economy of a smaller one. That's a tempting proposition, but our testing shows these small-displacement turbos are not delivering on the promises.

By now, we've tested many cars with these engines, and lots of competitors with traditional, naturally-aspirated powerplants, big and small. Generally, the turbocharged cars have slower acceleration and no better fuel economy than the models with bigger, conventional engines. Looking at EPA fuel-economy estimates (calculated based on laboratory tests), some of these cars' turbocharged engines seem to have an advantage. But we found those results don't match the findings from our own fuel-economy tests.

The latest example is the collection of EcoBoost Ford Fusions we tested, which come with small, direct-injection, turbocharged four-cylinder engines. The smallest one—a 1.6-liter producing 173 hp—is a $795 option over the basic conventional 2.5-liter four cylinder on Fusion SE models. But that car's 0-60 mph acceleration time trails most competitors, and its 25 mpg overall places it among the worst of the crop of recently-redesigned family sedans. The Toyota Camry, Honda Accord, and Nissan Altima, all with conventional 2.4- or 2.5-liter four-cylinder engines, get an additional 2, 5, and 6 mpg, respectively. And all accelerate more quickly.

The larger among Ford's EcoBoost four-cylinder engines, the turbocharged 231-hp, 2.0-liter, is billed as having the power of a V6 but delivering the fuel economy of a four-cylinder. However, our so-equipped Fusion Titanium returned 22 mpg (which pales against the 25 and 26 mpg we recorded for the best V6 family sedans), slower acceleration and reduced refinement compared to its V6-powered peers.

Another example is our tests of the Chevrolet Cruze. Our base Cruze had the 1.8-liter four-cylinder; our higher-end 1LT version came with the 1.4-liter turbo four cylinder. While the 1.4-liter feels marginally more powerful in daily driving, it was barely faster to 60 mph, and it got the same fuel economy as the larger engine—26 mpg overall.

Turbochargers pump extra air into the engine to deliver more power. But all engines have to be operated at a very specific air-to-fuel ratio. So this extra air has to be augmented with extra fuel, which may offset any savings from shrinking engine sizes.

One benefit to the turbocharged engines is an abundance of torque at low to mid rpm. In daily driving, this means a more effortless feeling of thrust with reduced need to downshift while climbing hills or when delivering the kind of moderate acceleration most drivers demand. That can make a car feel more responsive, even if its actual acceleration times from a standstill are slower. However, not all of these turbocharged models deliver that benefit. Many, especially those smaller 1.4- and 1.6-liter engines, still downshift frequently to keep up with traffic. And all but one of the tested cars have slower mid-range acceleration from 45-65 mph.

In contrast, BMW's turbocharged four-cylinder engines seem to deliver both good fuel economy and acceleration: The 2.0-liter turbocharged four cylinder contributes to 28 mpg overall in our last tested 328i sedan. It improved mileage only marginally in the 2013 X3 SUV compared to the six-cylinder 2011 X3 we tested, with essentially identical power and acceleration but somewhat comprised refinement. The 2.0-liter turbo four cylinder engine we've tested in Audis and Volkswagens usually return impressive mileage, though we haven't tested any identical model powered by two different engines for such a direct comparison.

I'm not sure I agree with that, be interested to know how they tested. The benefit of a turbo is that you're only using more fuel when on boost.

I'm not sure I agree with that, be interested to know how they tested. The benefit of a turbo is that you're only using more fuel when on boost.

Consumer Reports operates the largest and most sophisticated independent automobile testing center devoted to the consumer interest anywhere in the world. Situated on 327 acres in rural Connecticut, the Consumer Reports Auto Test Center is home to more than 20 staff members, including automotive engineers, technicians, and support staff. Consumer Reports buys, anonymously, all the cars it tests, about 80 per year, and drives each for thousands of miles.

Formal testing is done at the track and on surrounding public roads. The evaluation regimen consists of more than 50 individual tests. Some are objective, instrumented track tests using state-of-the-art electronic gear that yield empirical findings. Some are subjective evaluations-jury tests done by the experienced engineering staff. These videos will provide further insights into the ways that Consumer Reports evaluates new cars to help its readers make smart, informed choices. (Watch our car-review videos.) See our Guide to Consumer Reports Ratings.

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Fuel economy

We perform our own fuel-economy tests, independent of the government's often-quoted EPA figures and the manufacturers' claims. Using a precise fuel-flow measuring device spliced into the fuel line, we run three separate circuits. One is on a public highway at a steady 65 mph. That circuit is run in both directions to counteract any wind effect. A second is a stop-and-go simulated city-driving test done at our track. The third is a 150-mile "one-day trip" using several drivers taking turns around a 30-mile loop of public roads that include a highway section, secondary roads, and rural byways. CR's overall fuel-economy numbers are derived from those three fuel consumption tests.

The figures are generally atrocious. I haven't had a car in the last 20 years which couldn't manage over 40mpg...

Well, the BMW M535i would drop below 30 if hammered, but I still managed 40mpg on a 100mph tour across Germany.

My Laguna 2L petrol automatic made 42mpg, the Passat 2L petrol 50mpg, Mondeo 2L turbo diesel 50mpg, even my current Verso 2.2L turbo diesel automatic manages around 40mpg.

Yes but that consumer report is from the US, and they have lower efficiency standards and ultra efficient cars are not allowed to be exported to the US because of the impact on the fuel duty.

The USA has a smaller gallon, so obviously lower miles per gallon. 40mpg in UK is 33mpg in US gallons.

The USA has a smaller gallon, so obviously lower miles per gallon. 40mpg in UK is 33mpg in US gallons.

Doh! Of course.

Doh! Of course.