Code named L3B and built in GM’s Spring Hill, TN manufacturing plant, this turbocharged and intercooled gasoline 2.7-liter DOHC I-4 aims to provide Silverado buyers a breakthrough combination of power, torque, and fuel economy—minus a traditional four-banger’s noise and vibration. Chief engineer Tom Sutter explained, “Our goal was delivering 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.”
This clean-sheet, truck-only (thus far) engine has a deep-skirt, liberally ribbed die-cast aluminum block with iron liners. The 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.
Also consistent with current trends, the new 2.7-L is an under-square design with a 3.63-inch (92.25-mm) bore and a 4.01-inch (102-mm) stroke to facilitate compact, high-tumble combustion chambers. Side-mounted direct injectors deliver up to three injection events per combustion cycle and the 10:1 compression ratio and generates its SAE-rated output of 310 hp and 348 lb·ft (473 N·m) on 87-RON gasoline, Sutter noted.
Weight-saving measures such a nylon-reinforced plastic oil pan (another GM truck-engine first) and intake manifold and smaller-than-usual hollow-head fasteners yield an engine that’s 80 lb (36 kg) lighter than GM’s less-powerful 4.3-liter V6, which the new engine replaces as the base powerplant for the 2019 Silverado’s high-volume LT and RST mid-level trims.
Sutter is especially proud of the dual-volute turbocharger that delivers 22 psi (1.5 bar) of boost and a maximum 348 lb·ft (473 N·m) from 1500 to 4000 rpm. “One goal we achieved,” he noted, “was throttle response quick enough to provide 90% of peak torque in less than two seconds, which is significantly faster than our competition.”
Recently patented by BorgWarner, this turbo does a better job of exploiting exhaust-pulse energy to build boost more quickly than twin-scroll turbos. The key difference is that the twin-scroll exhaust passages are side-by-side while they are concentric in the dual-volute design. 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.
The new 2.7 brings several other advanced features to the full-sized pickup segment. Beyond the variable valve timing and stop-start used by GM for some time, this engine includes 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; low valve lift optimizes efficiency during part-throttle conditions, high lift maximizes power and torque. To curb fuel consumption during deceleration, the active fuel-management system also disables the two center cylinders’ exhaust valves.
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, this engine’s Active Thermal Management system dispenses with the traditional thermostat in favor of an electrically-driven water pump feeding a rotary valve to regulate three distinct cooling channels: one serving the block, a second to the cylinder head and a third line connected to the exhaust manifold and turbocharger’s center bearing. 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 includes when cylinders are deactivated.
During Automotive Engineering’s brief proving-grounds drive of a pre-production Silverado powered by the new 2.7-L, it performed as publicized without a hint of turbo lag or four-cylinder commotion. With gas prices on the rise, it will be the wise choice for pickup owners not requiring a V8’s energy reserve and will serve as competitive counterpoint to rival Ford’s longstanding downsized turbocharged Ecoboost engine choices for the F-150 fullsize pickup line.
2019 CHEVROLET SILVERADO 2.7L TURBO SPECIFICATIONS
|Type:||2.7L Turbocharged DOHC I-4|
|Bore & Stroke (in. / mm):||3.63 x 4.01 / 92.25 x 102|
|Block Material:||380 T5 cast aluminum|
|Cylinder Head Material:||356 T5 cast aluminum|
|Valvetrain:||Dual-overhead camshafts, four-valves per cylinder, tripower valvetrain with continuously variable valve timing, variable valve lift and Active Fuel Management|
|Air Delivery:||Single dual-volute turbocharger with electronically controlled wastegate; intercooling system. 22-psi / 1.5 bar max boost|
|Fuel Delivery:||High-pressure direct injection (3000 psi / 20 MPa) and electronic throttle control; Active Fuel Management|
|Ignition System:||High-energy coil-on-plug|
|Max Engine Speed:||6100 rpm|
|Additional Features:||Continuously variable oil pump; electric water pump; engine oil cooler, automatic stop/start, Active Thermal Management, exhaust manifold integrated in cylinder head|
(hp / kW @ rpm):
|310 / 231 @ 5600 (SAE certified)|
(lb.-ft. / Nm):
|348 / 473 @ 1500-4000 (SAE certified)|
|Manufacturing Location||Spring Hill, Tenn.|