Twin-turbo six engine

Twin-turbo six or conventional eight: Which works better in a full-size truck? When it comes to trucks, the engine inspires as much loyalty as the vehicle it powers. Mazda’s Skyactiv or Hyundai’s Tau engines will never haul in the licensing profits of the Power Stroke, Duramax, or Cummins names. And in light-duty trucks, the displacement also becomes the brand.

A Ram isn’t just powered by a Hemi, it’s a “Five-Seven.” A Silverado destined to earn its living better have the “Six-Two.” And if you were serious about building an F-series for work, it used to be that you ordered the old “Five-Four.” So Ford positioning its puny 3.5-liter twin-turbo EcoBoost V-6 atop the F-series lineup caused more than a few observers to choke on their chew. To see how the power structure shakes out, we lined up two nearly identical F-150S: one with the 5.0-liter V-8, one with the 3.5-liter twin-turbo EcoBoost V-6. Both are four-wheel-drive crew cabs with 5.5-foot beds. They pack the same six-speed automatic and 3.55:1 final-drive ratio. Aside from the turbocharged truck’s option to display a digital boost gauge, the interiors are indistinguishable. Even the paints are similar shades, just in case UV saturation affects weight. The EcoBoost F-150 did, however, come in 213 pounds heavier, in part due to its dual-pane sunroof and the FX4 package’s skidplates.

The powertrains are closely matched. The 5.0-liter makes 385 horsepower at 5750 rpm; the EcoBoost, 365 at 5000. But the V-6 has a big lead in torque, 420 pound-feet to 387, and it peaks 1350 revs lower than the V-8, at 2500 rpm. We took our pair to the test track and, after the regular procedure was complete, hooked a pair of identically loaded 6400-pound trailers to the hitches for extra acceleration and fuel-economy tests. And with that, deciding a finishing order got a little complicated.

5.0-LITER V-8
Unladen, the 5.0 trails the EcoBoost to 60 mph by a half-second, taking6-3 seconds versus 5.8. With trailers in tow, that gap grows to nearly two full seconds. From behind the wheel, the difference is astounding. Not that this should come as a surprise: Ford rates the EcoBoost’s towing capacity higher than the V-8’s, and our four-wheel-drive V-6 is rated to pull 11,500 pounds to the V-8’s 9000. (We chose less than the maximum load to represent what these trucks are more likely to encounter in everyday use.)

Still, such a significant load shines an unforgiving light on powertrain weaknesses. Laden, the V-8 needs a lot more pedal travel and a lot more revs than the EcoBoost does. From cruising speed, if you roll into the V-8’s throttle, you just keep on rolling in deeper and deeper until the throttle is wide open, waiting for a few more mph. With more than three tons out back, even moderate acceleration calls for full throttle or nothing. Under partial throttle, the turbocharged six gets things done that the V-8 can’t.

With the trailers unhitched, we appreciated the eight’s softer power delivery. In something so brick-shaped, any throttle prod necessitates a downshift regardless of the engine. But with the EcoBoost, those downshifts drop you into the meat of the torque band. We had to recalibrate our ankles to feather the six’s throttle a little to keep from surging forward. The eight’s natural power build results in smoother downshifts and acceleration.
And, surprisingly, the V-8 bettered the V-6 in fuel economy, the two tying while unladen and the 5.0 eking out a single-mpg lead while towing. As with other turbocharged engines, staying in the boost means consuming fuel. And as we barreled into a 25-mph headwind on our fuel-economy run, the boost gauge showed in real time how hard the six was battling the atmosphere. But while the “Eco” part of the turbo six’s designation is a stretch, the smaller engine’s capability is undeniable.

TWIN-TURBO 3.5-LITER V-6 Modern truck styling is equal parts International semi, Hamilton Safe, and well-marbled T-bone. Braggadocio matters with pickups. You might think that convincing buyers to give up the engine configuration that has powered nearly every iconic American vehicle over the last six decades would be a tough sell. But Ford claims the EcoBoost 3.5 is the highest-volume engine in the F-150 now. It can’t hurt that it costs just $600 to upgrade from the V-8 to the turbo V-6.

Unburdened, the EcoBoost six lunges forward with an eagerness the V-8 can’t muster. But the twitchy part-throttle power delivery is annoying and might have meant a different finishing order if not for the trailering portion of our test. The ease with which the Eco-Boost hauls a load—from a stop, under rolling acceleration, and cruising—positively embarrasses the eight. “But what about turbo lag?” traditionalists may whimper. A brief history of the term “lag”: It was coined at a time when the phenomenon meant you’d flat-foot the throttle and think, “Hmm, is something wrong?” furrow your brow and glance down at the shifter to make sure it was in the right gear, and finally feel the power start to come on several Mississippis after first demanding it. Modern turbo-chargers and engine controls mean that in the Ford, you get maybe a quarter of the way through “Hmm” before the full whack of torque eliminatesyour concerns.

Engineers were clearly hedging against cylinder-count bias when tuning the sound that is piped through the EcoBoost’s stereo. From the outside, the EcoBoost sounds like a turbo V-6. Inside, it’s not quite the barrel-aged Americana of the 5.0’s intake snort, but it’s close. This six has a better V-8 sound than a lot of actual V-8s. We had to find the boost gauge in the instrument cluster to make sure we hadn’t lifted ourselves into the wrong truck.
We can’t imagine a day when anybody tunes a V-8 to sound more like a V-6, and yet the 5.0’s engineers would do well to emulate the EcoBoost’s eagerness. They may not get a chance. We hear rumors that the 5.0-liter will be pulled from the F-150 next year. It seems like the time has come. Yes, the 5.0-liter is more relaxed and easier to live with in daily commuting. But in hardworking F-150S, twin turbos handily trump an extra pair of cylinders.

A TALE OF TWO CIVICS TURBOCHARGERS may be synonymous with big power and torque, but automakers have a very different motive for embracing forced induction. Smaller turbo engines fare better than naturally aspirated ones with similar performance on the EPA’s granny-like driving schedule. However, it’s not always clear if the fuel-economy advantage holds up on public roads with quicker acceleration and higher speeds.
To sniff out the real-world differences, we tested two Honda Civic sedans, each with the CVT, but one with the 174-hp turbocharged 1.5-liter four-cylinder and one with the 158-hp naturally aspirated 2.0-liter. By the EPA’s measure, the turbo Civic holds a 1-mpg edge on the highway with its 31/42-mpg ratings.

On a 300-mile loop of mixed highway, rural, and urban driving, the cars proved equally frugal by averaging 40 mpg. Digging deeper, we measured the steady-speed fuel consumption of the two Civics. Some of our results are astounding, such as the 50-pius-mpg both Civics achieve at 55 mph. The turbo wins across speeds ranging from 30 to 90 mph, with a 6-mpg advantage between 40 and 55 mph.

To generate the power required to maintain a particular cruising speed, any engine-small or large-must pump a corresponding amount of air. With equivalent gearing, the smaller engine requires a wider throttle opening to pump the same amount of air as a larger engine. Because pumping losses are lower with wider throttle openings, a smaller engine is more efficient.

Even at 90 mph, with the tach reading 2800 rpm, the turbo plays a minor role in cruise mode. This is precisely why nearly every carmaker will rely heavily on smaller-displacement, boosted engines to satisfy the fuel-economy mandate that requires a fleet-wide average of 54.5 mpg by 2025.

Spending the extra $1160 for the Honda’s turbo engine does have one clear advantage beyond efficiency: The additional power and torque clip 1.4 seconds from the zero-to-60-mph run and a full second off the quarter-mile time compared with the naturally aspirated alternative. But exceed the gentle, twinkle-toe throttle pressure we applied in our steady-speed tests and all efficiency bets are off. As boost rises, more fuel is injected and mileage drops. Precipitously.