TRUCK CAN RUN ON JUST ONE CYLINDER
Two features in Silverado will improve fuel economy, Jil McIntosh explains.
MILFORD, MICH. Last year, Canadians bought more than 425,500 trucks, and that’s a double-edged sword for companies that make them. Automakers have to meet average fuel economy numbers across their entire range, and lots of big-vehicle sales skewer the results. More than ever, new fuel-saving technologies are first coming out on trucks.
Chevrolet’s upcoming 2019 Silverado half-ton will feature a turbocharged four-cylinder engine, plus an all-new fuel management system on its V8 engines.
The premise behind both is to alter the engine’s size — not its physical mass, but how it operates internally — in response to how the truck’s being driven. The new 2.7-litre turbocharged four-cylinder can produce bigger-engine power when required, while the new Dynamic Fuel Management (DFM) system can run on a variety of cylinders, right down to just one as needed. GM says it’s the world’s first implementation on a production vehicle.
The basic technology of cylinder deactivation isn’t new, and several automakers use it. GM’s current version, called Active Fuel Management (AFM), is on the Silverado’s current V6 and V8 engines. The 2019 Silverado will offer the new DFM system on its 5.3- and 6.2-litre V8 engines only.
The difference is that when full power isn’t needed, AFM deactivates the same set of cylinders each time: the V6 shuts off two, the V8s shut down four. The deactivated pistons continue to move in their cylinders because they’re attached to the spinning crankshaft, but air and fuel aren’t drawn in, and the spark plug doesn’t fire.
The dynamic version shuts off cylinders the same way, but not necessarily the same ones each time. The “upgraded” engines, as GM calls them, have deactivation capability on all eight cylinders. There are 17 possible patterns of active and deactivated cylinders during each engine cycle of two crankshaft revolutions.
Horsepower and torque stay the same on the 5.3L engine, whether with AFM or DFM. The big question is the fuel economy difference, and those numbers haven’t been released yet. However, in comparative testing, the AFM version spent 60 per cent of its time on fewer than eight cylinders — and since most drivers seldom need all eight most of the time, they’ll likely see improvement at the pumps.
I drove the new engine on a short tour of GM’s test track, and the transition between cylinder modes is seamless. Most deactivation systems are, but it’s especially tough in an engine where the firing sequence shifts around so much. Getting it right involved working with the exhaust system so the sound didn’t change, and adding a pendulum in the torque converter to absorb vibration. The emissions system was tweaked so the oxygen sensor, which monitors exhaust to determine how much air and fuel the engine needs, would correctly interpret what was flowing past it during the different cycles.
New technology always comes with a price, and Chevrolet has adjusted the 2019 trim lines to accommodate it. The three lowest levels carry over the current 4.3L V6 and 5.3L V8, both with AFM, to keep the cost down.
Three mid-range trim levels offer the 2.7-litre turbo-four or the “upgraded” 5.3L V8 with DFM. The two highest trims offer the new 5.3- and 6.2-litre V8 with DFM; the old 6.2 with AFM is retiring. Next year, a 3.0L diesel engine will also be available.
I also got a short spin around the track with the new turbocharged engine. It’s smooth and strong, and with no discernible turbo lag, which GM’s engineers credit to a “dual-volute” turbocharger. The exhaust that powers the turbine wheel is directed into two separate streams that hit the wheel from two sides, so it spools up faster to reduce lag.
Thermal efficiency is improved with an electric water pump and a coolant control valve — basically an electronic version of a thermostat — that heat up the engine and transmission oil quickly after starting, and then keep the engine head cool for better combustion. The turbo-four also has cylinder deactivation, running on just two when full power isn’t needed. This is achieved with a sliding camshaft, which can activate the valves at high lift for full power, low lift for cruising, or shut off those two cylinders as required.
GM will now have the second brand of trucks available with a turbo, since Ford’s been there for a while with the F-150’s EcoBoost engines. The new Silverado’s turbo-four makes 310 horsepower and 348 pound-feet of torque; GM compares it to the F-150’s base, non-turbo 3.3L V6 engine, which isn’t as powerful.
That’s not quite fair, though, since the F-150 also offers a 2.7-litre V6 turbocharged engine, making a superior 325 hp and 400 lb-ft of torque. It’ll come down to the numbers that GM isn’t currently discussing — fuel efficiency and towing/payload capability — to see how much a difference you get between four and six cylinders.
My time in the truck was very limited, but at first glance, it rides and handles well, and engine performance is impressive. These new engines will also be used in the GMC Sierra, with pricing, fuel economy and other stats coming out closer to launch later this year.
Driving