Contributed by Bob Chabot
GM Debuts First Four Cylinder Engine for Full-Size Pickups
New 2.7L turbo engine delivers V6 performance
General Motors (GM) says it will introduce a world first later this year — the first full-size pickup to offer a 4-cylinder engine. The automaker is offering the new powertrain as one of six options available in the 2019 Silverado pickup lineup. While rival Ford Motor Co. had previously introduced its popular 2.7-liter V6 Ecoboost engine on its F-150, the Silverado will be the first full-size pickup to offer a 4-cylinder engine.
Code named “LB3” the new four-cylinder powerplant will be built in GM’s Spring Hill, TN manufacturing plant. The turbocharged and intercooled gasoline 2.7-liter DOHC I-4 aims to provide Silverado buyers a breakthrough combination of power, torque and fuel economy, without the traditional four-banger’s noise and vibration.
“We asked what would work best for this truck, focusing on less noise and vibration and less mass,” shared GM’s Chief engineer Tom Sutter. “Our goal was to deliver leading-edge towing and hauling performance with unprecedented smoothness. Development tests suggest that this new four will offer Silverado customers an excellent alternative to six- and eight-cylinder gas and diesel engines.”
The 2019 Silverado LT and RTS trim levels will pair GM’s LB3 2.7L four-cylinder turbocharged engine (left) with GM’s 8L90 8-speed automatic transmission (right) as the standard offering. The powerplant features newly patented dual-volute turbocharger with electronic boost control sourced from BorgWarner. (Images — GM)
Technical Highlights Include New Camshaft and Turbocharger Design
Sutter says the new 2.7-liter engine runs on 87-RON gasoline and is more powerful and efficient than the 4.3-liter V6 it replaces. The LB3 engine’s 10:1 compression ratio delivers 310 horsepower and 348 pound-feet (472 Nm) of torque. Its design features a 3.63-inch (92.25-mm) bore and a 4.01-inch (102-mm) stroke to facilitate compact, high-tumble combustion chambers.
The new four-cylinder engine introduces an all-new camshaft design developed internally by GM. It features an electromagnetically actuated sliding lobe assembly that automatically provides the most appropriate of three different intake cam profiles to balance efficiency and power:
Sutter added side-mounted direct injectors will deliver up to three injection events per combustion cycle and includes fuel-saving cylinder deactivation technology. To curb fuel consumption during deceleration, the Dynamic Fuel Management (DFM) system will disable the two center cylinders’ exhaust valves. (Note: On other Silverado variants with larger V6 and V8 engines, DFM functionality will be expanded to allow it to shut off two cylinders at cruising speeds, using computer algorithms to choose between 17 different operating modes.
- Low valve lift optimizes cruising efficiency during part-throttle conditions.
- High valve lift maximizes power and torque.
- Zero valve lift occurs during cylinder deactivation, when the active fuel-management system disables the two center cylinders’ exhaust valves during light load, such as when decelerating.
The LB3’s 16-valve aluminum head uses new copper-alloy exhaust valve guides for improved heat transfer. Dual balance shafts and a variable-output oil pump are supported by a bolt-on aluminum lower-block module extending well below the forged-steel crankshaft’s main bearings. In a now well-accepted basic-design technique, the crankshaft is offset from the cylinder bore centerline to reduce friction from piston side loading.
Other features of the new 2.7L four-cylinder engine include:
“One goal we achieved,” Sutter noted, “Was a throttle response quick enough to provide 90 percent of peak torque in less than two seconds, which is significantly faster than our competition.” Based on turbo technology with electronic boost control, sourced from and recently patented by BorgWarner, this turbo does a better job of exploiting exhaust-pulse energy to build boost more quickly than twin-scroll turbos; hence, next to no turbo lag.
- An integrated exhaust manifold on the cylinder head assembly promotes faster engine warmup and quicker turbo response.
- A variable-pressure oiling system with a continuously variable-displacement vane oil pump enhances efficiency by optimizing oil pressure as a function of engine speed and load. With it, the oil supply is matched to the engine requirements rather than the excessive supply of a conventional, fixed-displacement oil pump.
- Oil jets located in the block are employed for performance and temperature control. They target the underside of the pistons and the surrounding cylinder walls with an extra layer of cooling, friction-reducing oil. The jets reduce piston temperature, allowing the engine to produce more power and enhance long-term durability.
- Direct fuel injection is used to optimize efficiency and performance. With direct injection, a higher compression ratio (10.0:1) is possible because of a cooling effect as the injected fuel vaporizes in the combustion chamber, reducing the charge temperature and improving resistance to spark knock. Direct injection also enables gas scavenging from the combustion chamber to the turbo for fast response.
- Dual overhead camshafts contribute to the 2.7L Turbo’s smoothness and high output, with dual independent continuously variable valve timing working with the valvetrain to deliver optimal performance and efficiency. The dual independent system, which allows the intake and exhaust valves to be phased at different rates, promotes linear delivery of torque with near-peak levels over a broad rpm range, and high specific output (horsepower per liter of displacement) without sacrificing overall engine response or drivability.
- Stop/start enhances fuel economy in city driving. The driver-selectable system shuts off the engine at stoplights and certain other stop-and-go situations, saving fuel. The engine automatically restarts when the driver takes his foot off the brake.
“The key difference is that the twin-scroll exhaust passages are side-by-side while they are concentric in the dual-volute design,” Sutter added. “Since the points where the two flow paths engage the turbine wheel are more widely separated with dual volutes, more pulse energy is available to spin the wheel. The new dual-volute design also is said to be less susceptible to flow ‘short-circuiting’ where the two exhaust streams exit the turbine housing.
Although full specifications — including payload capacity and fuel economy ratings — haven't yet been disclosed, GM Chief Engineer Sutter said they will be comparable to larger V-6 offerings from Ford and Ram.
High-Tech Thermal Management
“To speed engine, cabin and automatic transmission warmup following a cold start and to maintain even temperatures in all four cylinders, the new 2.7L turbocharged engine’s Active Thermal Management system dispenses with the traditional thermostat in favor of an electrically-driven water pump that feeds a rotary valve to regulate three distinct cooling channels. One serves the engine block, the second the cylinder head and the third line is connected to the exhaust manifold and turbocharger’s center bearing.
The engine also receives an electric water pump instead of an engine-driven pump to enhance efficiency and ensure stable cabin temperatures when the stop/start system shuts off the engine. A processor-controlled vane-type oil pump provides a regulated amount of bearing, bore, and valvetrain lubrication, plus squirts to cool the pistons during high-load conditions.
The new 2.7-L engine will be paired with the 8L90 Hydra-Matic automatic transmission. The 8-speed features a new centrifugal pendulum absorber that helps counteract torsional vibration that occurs when cylinders are deactivated. The new drivetrain is surprisingly quiet and accelerates without turbo lag.
BorgWarner’s eBooster provides the new 2.7L four-cylinder engine with improved transient performance and fuel efficiency. (Image — BorgWarner)
Expanding the Range of Choices
“A major focus of the next-generation Silverado is expanding the range of choices,” said Tim Asoklis, one of the engineers on Sutter’s team. With average gas prices once again approaching $3 per gallon, fuel economy matters.
But as with all pickup trucks, it's the performance that buyers care about most. Trucks are work tools, after all, and owners expect them to do the job. But the broadened Silverado lineup will allow GM to offer a range of models tailored to buyers' differing needs for performance, efficiency, technology and value.
“GM will start building the 2019 Silverado 2.7L models this fall," Asoklis explained. “With all-new engines and a broader model range, there’s now a Silverado for everyone, whether you’re buying your first pickup or your tenth.”
[Editor's note: Visit MOTOR.com for the latest diagnostic and service insights.]