PHOENIX — When you make big investments in a pickup to improve fuel economy — think Ford's aluminum-body F-150 or the mild-hybrid system on Ram's 1500 — you expect significant results.
So how does General Motors explain shifting to a four-cylinder turbo for its redesigned full-size pickups and getting little gain in combined EPA fuel economy ratings over the previous generation's V-6?
As a work in progress.
"I don't think we're done with the fuel economy piece yet," said Tim Herrick, executive chief engineer of GM's full-size trucks, during a Silverado media drive here. "We learn more and more every day."
Squeezing fuel economy gains out of pickups is never easy. Ford's 2015 aluminum F-150 with a then-new 2.7-liter V-6 initially gained up to 4 mpg combined, while Fiat Chrysler Automobiles' 2019 Ram 1500 with eTorque gained up to 2 mpg overall. Those gains don't sound big, given the billions of dollars invested, but in percentage terms, they are huge, and their environmental impact — as measured by federal regulators — is magnified by the trucks' enormous sales volumes.
Small improvement
The EPA rated GM's 2.7-liter engine at 20 mpg city/23 highway/21 combined. While the city rating is up 13 percent, the combined rating is just 1 mpg more than for the 4.3-liter V-6 that the four-cylinder replaces as the standard volume engine. The 4x4 models get 1 mpg less.
That puts GM's four-cylinder in line with comparable truck engines from Ford (3.3-liter V-6) and FCA (3.6-liter V-6 with a light hybrid system) that are rated at 22 mpg combined. Ford's 2.7-liter V-6 is rated at 22 combined mpg.
Those engines, however, offer up to 25 or 26 mpg on the highway.
"If you're delivering on everything, and you're getting the same fuel economy, the question is, 'Why?' " said Stephanie Brinley, principal automotive analyst at IHS Markit.
GM officials argue the EPA ratings don't tell the whole story. As with diesel engines, they say, fuel economy will be better in the real world than its predecessor and will at least match comparable V-6 models from competitors.
"Don't look at the label," said Herrick. "We're as good or better than them in every step."
EPA testing methods as well as a larger design footprint also may have played a role in the lower-than-expected ratings, which GM may look to address soon.
GM said the four-cylinder engine still delivers in other ways. It's rated at 310 hp and 348 pound-feet of torque, vs. 285 hp and 305 pound-feet of torque for the 4.3-liter V-6. It's paired with an eight-speed transmission and will be standard on the new Silverado RST and popular Silverado LT trims.
"Whatever they've done to create this engine now, they'll be able to improve it going forward," said Brinley, adding that automakers routinely improve fuel efficiency on new engines.
GM said the new engine package goes from 0 to 60 mph in less than 7 seconds and weighs 380 pounds less than the previous model. GM also made changes to reduce turbo lag.
"We wanted it to exceed our customers' expectations, all while delivering requirements that the government has set," said Kevin Luchansky, engine architect and assistant chief engineer of the 2.7-liter turbo. "The fact that it doesn't have two more cylinders on it doesn't hurt our customers at all."
Racing fuel
Getting the engine from lines on paper to production in four years didn't come without challenges.
An early iteration of the engine would hit GM's desired targets only if it ran on racing fuel, Luchansky said.
"You can't sell a pickup truck and need it to run on race gas," he said. "So we had a lot of work to do."
Some of that work included contracting a third party — a common practice — to help with combustion development to deliver low-end torque comparable to a diesel.
The focus on low-end torque was crucial, Luchansky said, because it provides better acceleration where drivers spend most of their time and helps with fuel economy in those settings. Chevrolet expects about 10 percent of Silverado sales to be the 2.7-liter engine, said Sandor Piszar, Chevrolet truck marketing director.
Brinley said that despite the EPA's fuel economy numbers, if the four-cylinder trucks indeed perform better in real-world driving, that's "more important" to consumers than a number on the sticker.