New Silverado engine showcases technology improvements

by Jim KerrAuto Tech . Sep 07 2018
General MotorsThe 2019 Chevrolet Silverado will be available with a turbocharged 2.7-litre four-cylinder engine.

General Motors

The 2019 Chevrolet Silverado will be available with a turbocharged 2.7-litre four-cylinder engine.

Hybrid and electric technology continues to improve, but so does the technology in gasoline-powered internal combustion engines. The new 2.7-litre, Turbo four-cylinder engine being offered in the 2019 Chevrolet Silverado pickup is a great example of the improvements possible with a gasoline engine.

With 310 horsepower and 348 pound-feet of torque — 22 per cent more than the 4.3-litre V-6 it replaces — General Motors’ new 2.7-litre turbo engine was designed specifically for trucks and delivers its peak torque from 1,500 to 4,000 r.p.m. According to Tom Sutter, chief engineer for the engine, “the new 2.7-litre Turbo is a technological marvel, with our most advanced valve train.”

There are three separate technologies used in the valve train, which work together to maximize performance. The engine is GM’s first turbo engine to use active fuel management, which deactivates two cylinders under light loads by keeping valves closed and turning off fuel injectors. This maximizes fuel economy. The valves are reactivated again within two revolutions of the crankshaft when power is needed, which at a cruise of 2,000 r.p.m. takes only .06 seconds!

Continuously variable valve timing technology helps the 2.7-litre deliver strong engine torque at low r.p.m. while providing more engine efficiency at higher r.p.m. . The third technology uses an electro-mechanical variable valve lift system that provides alternate camshaft lift profiles. The electromagnetic actuators shift a moveable shaft that contains different cam lobes so both the intake and exhaust valves can change the amount of lift. A low lift profile on the shaft gives optimum fuel efficiency at low and medium r.p.m. , while the high lift profile allows more airflow past the valves at high r.p.m. to maximize power. It’s like having two engine designs in one package — one for fuel economy and one for performance.

Low r.p.m. torque is improved by the use of long stroke piston design. A long stroke (the distance the piston moves up and down in the cylinder) increases the torque by using more of the combustion pressure on the top of the piston and the added leverage applied to the crankshaft. A downside of a long stroke design is that it places more load on the piston skirts and creates more internal friction. To help alleviate that, the forged steel crankshaft (rather than cast steel) is positioned slightly off-centre in the aluminum engine block so the piston and connecting rod push more directly down when there is maximum pressure on top of the piston. The engine also incorporates oil jets that spray the bottom of the pistons, which help cool the pistons and provide additional lubrication for cylinder walls.

The turbocharger used on this 2.7-litre engine is a dual-volute design that uses two separate chambers and nozzles to direct exhaust gases from the engine to the turbine wheel. This design provides quicker turbocharger response and enhanced low r.p.m. engine torque. The engine’s exhaust manifold is integrated with the aluminum cylinder head and splits the exhaust channels so the gases are directed to the two turbocharger passages. This split channel design also helps scavenge the exhaust gases out of the engine for improved performance.

A charge-air cooler (intercooler) is connected between the turbocharger compressor outlet and the engine intake to cool the intake air that was heated as it was compressed. The charge-air cooler lowers the air temperature by about 74 C. Lower air temperature makes the air denser, so more can be pumped into the engine for more torque.

Other technologies built into this engine include a variable displacement vane-type oil pump that changes oil flow to reduce parasitic power losses. An electric water pump is also used for the same reason, plus it can also provide heat to the passenger compartment when the engine is operating in start-stop mode. Active thermal management is unique in that it uses a rotary valve system to change the coolant flow through the engine so that hot coolant is sent to heat specific locations for a quicker engine warm-up and cool parts when needed for performance. This 2.7-litre turbo engine is a clean sheet design, started from scratch to utilize the latest technologies and produce the type of power needed for truck use with the fuel economy today’s drivers seek.

james.kerr@sasktel.net