Ford, GM take opposite routes to engine fuel economy

General Motors and Ford Motor Co. are using radically different strategies to raise the fuel economy of their thirstiest vehicles: trucks and performance cars.

Ford, with its EcoBoost turbocharging technology, makes a small engine act big.

GM, with its Active Fuel Management cylinder deactivation system, makes a big engine act small.

Whose strategy is better? It depends on how success is measured.

If cost and manufacturing complexity and real-world fuel economy gains are the metrics, GM has the advantage.

But if sales, image and government-measured fuel economy improvements are the yardsticks, Ford gets the nod.

According to the EPA's annual Trends Report released Dec. 12, GM and Ford have increased car and light-truck fuel economy over the past three years. But Ford has registered a slightly bigger gain, with its fleet rising 7 percent, from 21.1 mpg to 22.6, while GM's fleet has increased 6 percent, from 20.7 mpg to 22.0.

The miles-per-gallon figures in the Trends Report are calculated using automakers' yearly sales of cars and light-duty trucks.

EcoBoost: More power, torque

All six of Ford's overhead-cam EcoBoost engines have four valves per cylinder and incorporate three technologies: turbocharging, direct fuel injection and variable valve timing. The formula dramatically increases an engine's horsepower and torque. Nearly all of Ford's EcoBoost engines are rated at 120 hp or more per liter. Nonturbo engines usually develop between 70 and 80 hp per liter.

That high output enables Ford to replace a V-8 with a smaller and lighter V-6 with no performance loss. Likewise, its four-cylinder engines deliver the power of a V-6, again with no performance loss. Ford claims this strategy yields about a 20 percent fuel economy gain.

The latest EcoBoost engine is a 1.0-liter three-cylinder in the Fiesta subcompact that makes more horsepower and torque than Ford's 1.6-liter four-cylinder and has an EPA highway rating of 45 mpg. Ford's downsize-and-boost strategy has been successful. Since launch in 2010, Ford has sold nearly 800,000 EcoBoost equipped vehicles in North America, including 400,000 F-150 pickups with V-6 engines. EcoBoost has become one of Ford's most widely recognized subbrands.

Still, there's a chink or two in the EcoBoost armor. EcoBoost can deliver the estimated fuel economy if the driver uses the turbocharger sparingly. But if the motorist uses the turbocharger a lot, fuel economy likely will fall short of the estimated mpg. And when pulling a trailer with an EcoBoost-powered F-150, fuel economy can dip into single digits, according to comments on f150forum.com. Ford also has had to recall around 170,000 Escapes because of quality glitches with the 1.6-liter EcoBoost engine. The top-selling EcoBoost-equipped vehicle, the F-150, also has had problems. Moisture collecting in part of the turbo system, the charge air cooler, caused the truck to stumble or stall, and Ford had to replace the part under warranty.

GM: Cylinder shut-offs

The Active Fuel Management system GM uses on its 4.3-liter V-6 and 5.3- and 6.2-liter V-8 engines could not be more different from EcoBoost.

Over the years, GM has taken some lumps from critics for sticking to its overhead valve "small block" engine architecture that dates to the 1950s. The layout places the cam in the center of the engine, where it operates the valves with pushrods and rocker arms. It is low-cost and low-tech compared with overhead-cam engines. But cylinder deactivation works with less complexity and expense on pushrod engines than on overhead-cam engines.

GM's system shuts down two cylinders under light load conditions, such as when cruising at a steady speed. It turns a V-6 into a V-4 and a V-8 into a V-6.

Air trapped in the deactivated cylinders acts as springs and reduces engine drag. GM has spent years tweaking the technology. It is now so seamless that most drivers can't feel the engine as it switches cylinders off and on, although engine noise is slightly higher when the system is operating. GM says Active Fuel Management yields about 7.5 percent better fuel economy.

The knock on Active Fuel Management is that the rpm range that it works in is narrow and even the slightest pressure on the accelerator will switch off the system. GM owners reporting their fuel economy on forums and on the EPA's fueleconomy.gov Web site show real-world performance very close to the window label number. Some drivers claim to get higher than the EPA window label number. But when towing, Active Fuel Management-equipped engines suffer the same fate as EcoBoost: Hook up a heavy load and the fuel economy plummets.

Still, EcoBoost and Active Fuel Management can deliver impressive fuel economy gains -- if used judiciously.

Consider the new 4.3-liter V-6 base engine in the Chevrolet Silverado, GM's highest volume nameplate. It carries a 24 mpg highway fuel economy rating, up from the 20 mpg in the old V-6 truck and -- more important -- 2 mpg higher than Ford's F-150 with its 3.5-liter EcoBoost engine.

"When Ford brought out its modular V-8 engine family in the 1990s, the focus wasn't on fuel economy," said AutoPacific analyst Dave Sullivan. Performance and technology were more important, he said.

Some estimates place the cost of installing Active Fuel Management -- oil-pressure operated solenoids that turn off valve lifters, and computer controls -- at between $50 and $100 per vehicle. Meanwhile, Ford's turbochargers, intercoolers, heat abatement and other equipment that make up EcoBoost likely costs at least five times more depending on the application, experts say.

Ford charges a minimum of $1,000 to add an EcoBoost engine to a vehicle.

GM charges nothing extra for Active Fuel Management, which comes standard on the 4.3-, 5.3- and 6.2-liter engines.

Active Fuel Management helps give the 6.2-liter, 455-hp Chevy Corvette an impressive 29 mpg EPA highway rating.

"Now, pushrods make sense again," Sullivan said.

Downsized the right size?

Top engineers for GM and Ford are convinced they've chosen the right technology for their companies.

Jordan Lee, GM's chief engineer for small block engines, said GM considered its own versions of downsized and boosted engines.

"We have found that when you take a really small engine and put it in a larger mass vehicle, you really stretch the engine's operating envelope," he said. "It is under boost a lot of the time just for normal drivability.

"The real-world fuel economy does indeed suffer. So, we did the analysis on AFM naturally aspirated engines, especially in trucks. It was a really good match for fuel economy optimization as well as drivability."

Ford, which claims to have more vehicles with the smallest engines in their class than any other automaker, is on a mission to reduce engine size and vehicle weight. Ford has pledged to cut vehicle weight at each redesign by between 250 and 750 pounds. Replacing a V-6 with a four-cylinder EcoBoost saves about 100 pounds in some vehicles.

But downsizing engines is not an exact science, and Ford has had a misfire. The 2.0-liter four-cylinder engine in the 4,900-pound all-wheel-drive Explorer crossover, for instance, has sold poorly.

Ford in 2014 is launching a bigger four-cylinder EcoBoost engine, a 2.3-liter rated at about 300 hp. The engine will find its way into the Lincoln MKC and Ford Mustang and is expected to be offered in the Explorer.

Balancing mpg, fun

"What we know is that powertrain matching is very important when specifying an EcoBoost engine," says Bob Fascetti, Ford's vice president of powertrain engineering.

"We provide the right balance between great fuel economy and 'fun to drive.' We start with operating the engine in the ideal efficiency zone and then add in the fun to drive elements. If you downsize too far, then you cannot operate long enough in the high efficiency regions while providing ideal performance."

EcoBoost technology is Ford's global fuel economy play for gasoline engines. Nearly every Ford vehicle in North America is available with an EcoBoost engine, and some, such as the Fiesta, Fusion, Escape and Taurus, are offered with two EcoBoost options.

GM's fuel economy strategy relies on Active Fuel Management only for its largest engines, which are mostly sold in North America in trucks and rear-wheel-drive performance cars, such as the Chevrolet Camaro and Corvette.

The next leap in fuel economy will likely benefit both companies equally. GM and Ford signed a pact to create a new generation of nine-speed front-wheel-drive and 10-speed rwd transmissions.

Fascetti and Lee say these new transmissions will enable engines to stay in the "sweet spot" -- or most efficient rpm range -- longer than the six-speed transmissions the companies now use.

Meanwhile, the pressure is on for GM and Ford to keep increasing fuel economy. By the 2025 model year, automaker fleets must achieve 54.5 mpg. To reach that goal, both companies have to improve fuel economy about 5 percent a year.