The GM L3B is a turbocharged gasoline engine produced by General Motors for the use in full-size pickup trucks. Displacing 2.7 liters in an inline-four cylinder configuration, the L3B is a clean-sheet design for General Motors. The engine was developed from the outset as a truck engine.

Overview

The GM L3B engine made its debut in the 2019 Chevrolet Silverado 1500 and 2019 GMC Sierra 1500 producing a SAE-certified 310 horsepower and 348 pound-feet of torque.

The motor was developed specifically for truck applications, and the motor delivers peak torque from 1,500 to 4,000 rpm. Additionally, it makes 22 percent more torque than the 4.3L V-6 LV3 it replaces.

Designed as a truck engine

To help generate the strong low-end torque customers expect in a truck, it was designed with a long piston stroke of 4.011 inches (102mm), which is the distance the piston travels up and down within the cylinder.

The long stroke enables improved combustion and thus a higher compression ratio. Typically, a long stoke can increase  the load of the pistons against the cylinder walls, generating more friction. That’s alleviated in the 2.7L Turbo with an offset crankshaft. It is slightly off-center of the cylinders, allowing a more upright position for the connecting rods during their movement.

To support the high cylinder pressures that come with turbocharging, the crankshaft and connecting rods are made of forged steel and the pistons are made of a tough aluminum alloy with a cast iron ring groove insert.

All elements of the 2.7L Turbo were designed for the demands of turbocharged performance in a truck environment, and the engine  was subject to the same rigorous durability standards as the Silverado’s proven V-8 engines.

The 2.7L Turbo features an aluminum block and cylinder head for reduced mass.

Unique Valvetrain Offers More Precise Control

The cornerstone of the 2.7L Turbo L3B is an innovative double overhead cam valvetrain that enables:

• GM’s first use of Active Fuel Management (cylinder deactivation) on a four cylinder engine.
• High and low lift valve profiles.
• Continuously variable valve timing. 

In fact, the innovation valvetrain is GM’s first to incorporate variable lift, duration and Active Fuel Management to optimize performance and efficiency across the rpm band. It is a key reason the engine’s peak torque is available at only 1,500 rpm.

The system’s electro-mechanical variable camshaft effectively allows the engine to operate with three different camshaft profiles, complementing the variable valve timing system to deliver optimized operating modes for different engine speeds and loads:

1. High valve lift for full power,
2. Low valve lift for balance of power and efficiency.
3. Active Fuel Management shuts down two of the cylinders in light load conditions to further conserve fuel.

The camshaft design alters the lift of the intake and exhausts valves. As the engine load changes, electromagnetic actuators allow a movable shaft containing different cam lobes to shift imperceptibility between high-lift and low lift profiles.

Lift is the distance the valve travels from its seat when opened, and duration is the amount of time the valve remains open. Higher lift and longer duration allow more air to flow into the combustion chamber, so the system’s high-lift lobe profile enhances performance at higher rpm, while the low-lift profile optimizes efficiency at low and mid range speeds.

Dual-Volute Turbocharger Builds Torque

The 2.7L Turbo engine employs an advanced dual-volute turbocharger that elevates the performance and efficiency advantages of a conventional turbo, with quicker response and enhanced low-rpm torque production.

Rather than a single spiral chamber (volute) feeding exhaust gas from the exhaust manifold to drive the turbine on the turbocharger, the dual volute designed has a pair of separate chambers with two exhaust gas inlets and two nozzles to drive the turbine. The design allows the exhaust pulses of the engine to be leveraged for faster spool-up and subsequent boost production, particularly at low rpm, where the effect significantly enhances torque output and drivability.

It works in unison with the engine’s integrated exhaust manifold/turbocharger housing, with splits the exhaust channels from the cylinder head so the exhaust flows through two separate channels in the turbo housing, based on the engine’s exhaust pulses. When complemented by the precision of the engine’s valvetrain, that separation leverages exhaust scavenging techniques to optimize gas flow, which decreases exhaust gas temperature, improves turbine efficiency and reduces turbo lag.

An electronically controlled wastegate and charge-air cooling system support the turbocharger and enhance its effectiveness. Compared to a conventional wastegate, the electronically controlled version offers more precise management of the engine’s boost pressure for smoother, more consistent performance.

With the charge-air cooler, the pressurized, heated air generated by the turbocharger is pumped through a heat exchange before it enters the engine. That lowers the air charge temperature by about 130 degrees  F (74 C), packing the combustion chambers with cooler, denser air that enhances power production. The system achieves more than 80 percent cooling efficiency with less than 2 psi (12 kPa) flow restriction at peak power, contributing to the engine’s available torque production at low rpm.