Turbos don’t always boost fuel economy
Automakers have used turbochargers to boost performance for more than 50 years, but in recent times they have evolved from a niche performance feature to a mainstream offering aimed at improving fuel economy.
Sales of turbocharged engines grew from five per cent of new vehicles in the U.S. in 2008 and 2009 to 23 per cent in 2016, according to J.D. Power, or slightly more than four million vehicles.
Faced with more stringent corporate average fuel economy standards, automakers are installing turbochargers on small engines to replace larger engines and improve their fuel-economy numbers without sacrificing performance, David Amodeo, a senior manager at J.D. Power, said in a telephone interview.
“They’re putting them in their vehicles for fuel efficiency. You can get the same horsepower, and you can get really good driving characteristics out of a much smaller engine,” Amodeo said. “This is going to become more and more commonplace, and I don’t expect that growth to slow down. We’re going to see turbos in all sorts of applications.”
The biggest increases were among luxury vehicles. J.D. Power said 57 per cent of premium cars and 49 per cent of premium SUVs came with turbos. In contrast, turbos were installed in 21 per cent of nonluxury passenger cars and 14 per cent of nonluxury SUVs last year. Luxury brands such as BMW, Mercedes-Benz and Audi now offer turbochargers on most or all of their model lines, and many are 2.0-litre four-cylinder engines.
In the past, the primary focus of turbocharging was to raise horsepower on performance cars. Today, though, they are widely used to also improve fuel economy in family vehicles such as the Chevrolet Malibu, Ford Escape, Honda Civic and Hyundai Tucson. Midsize family cars such as the Malibu and Ford Fusion that formerly came with V-6 engines and large four-cylinder engines now have turbocharged engines as small as 1.5 litres, a size that used to be confined to subcompact cars.
Ford, one of the earliest to go all-in with turbocharging, sold nearly 1.2 million turbocharged vehicles in the U.S. last year, 47 per cent of its 2.5 million total U.S. sales.
Turbocharged engines can deliver more torque than larger engines, which is especially useful in sports cars and pickup trucks.
The base engine in the 2017 Ford Mustang is a 3.7-litre V-6 with 300 horsepower and 280 poundfeet of torque, but an optional 2.3-litre turbocharged four-cylinder produces 310 horsepower and 320 pound-feet of torque. In addition, the turbo engine has a higher EPA fuel economy estimate, 24 mpg combined versus 21 mpg for the V-6. Ford says it will drop the V-6 for 2018 and make the turbo four-cylinder the base engine.
With full-size pickup trucks, V-8 engines have dominated for years, and turbochargers previously were limited to heavy-duty diesel models. At Ford, though, nearly 70 per cent of its light-duty F-150 pickups are sold with EcoBoost V-6 engines, the company’s brand name for its turbos.
Steve Russ, Ford’s technical leader for internal combustion engines, said Ford chose smaller turbocharged engines as a more efficient solution than cylinder deactivation, which shuts down some cylinders of a V-8 or V-6 engine at highway speeds to save fuel.
With cylinder deactivation, a bigger engine behaves like a smaller one, but Russ said in a telephone interview, “We’re taking a smaller motor and making it look bigger.”
A large engine is less efficient than a smaller one in normal driving, when it is operating well below its peak performance levels, and a smaller engine with a turbo can deliver peak performance when needed.
“The peak capability is covered by the [turbo] boosting, and then you have a smaller motor that is operating in a more efficient zone during normal driving, so it provides significantly more fuel economy,” he said.
Russ said Ford subjects its EcoBoost engine to the same performance and durability requirements as its nonturbo engines.
Consumers, though, have had issues with turbocharged engines across several brands, Amodeo said, and fuel economy has been a particular sore point.
“The caveat is that on the EPA’s test cycle, these engines look fantastic from a fuel efficiency standpoint for the window stickers, but some consumers are saying, my fuel economy is horrible, because they have to sink their foot into it more because the engine has to work harder to generate that power,” Amodeo said.
In J.D. Power’s 2016 Vehicle Dependability Study, which is based on 2013 vehicle owner responses after three years of ownership, turbos had nearly 30 per cent more complaints than nonturbos. That includes all types of complaints, such as responsiveness and fuel economy, not just mechanical failures or warranty claims.
Turbo engines did not have more complaints in Power’s 2016 Initial Quality Study, which assesses problems in the first 90 days of ownership of 2016 model year vehicles. Amodeo said that could indicate manufacturers have improved the overall performance and responsiveness of turbo engines.
Consumer Reports magazine also has found in its real-world driving tests that turbo engines may not live up to the higher fuel economy estimates generated in the EPA tests.
“What we’ve found in some situations is that they may have better EPA fuel economy [estimates], but when we’ve tested the fuel economy in our regimented test cycle we’ve found that they don’t always deliver. Sometimes they’re actually worse than the larger, normally aspirated engines in our testing,” said Jake Fisher, director of automotive testing for Consumer Reports.
The difference, he added, is that the EPA tests simulate real-world driving and “are very gentle, so you’re not pushing the engine very hard.” In the real world, drivers will often use a heavy throttle foot to activate the turbo for a burst of acceleration.
“Don’t assume that because it’s labelled EcoBoost or Ecotec or that because you’re getting a smaller engine you’re going to be getting better fuel economy,” Fisher said.
“It’s very possible that the smaller engine may be consuming more fuel than the larger, non-turbo engine.”