How Chevy made Its 3.0L Duramax Diesel Inline-Six So Efficient
The key, Chevy says, was starting from scratch.
Chevrolet invited us out to Bend, Oregon to test its new diesel 3.0-liter turbocharged inline-six Duramax engine in the updated 2020 Silverado pickup. The new powerplant produces 277 horsepower at 3,750 rpm and 460 lb-ft of torque at 1,500 rpm and is mated to a 10-speed automatic. Although EPA figures haven't been released yet, we hypermiled a regular-cab, two-wheel-drive model on a windy day and averaged a whopping 44.7 mpg. (Figure on a rating something like 26-30 mpg on the highway.) We spoke with chief engineer Vincenzo Verdino and assistant chief engineer John Barta about how they achieved such a powerful yet efficient engine.
The engine was built from the ground up to maximize fuel efficiency without sacrificing power or torque. Barta told us that Chevy's engineers "optimized the air intake, the turbocharger, the exhaust system" packaging specifically for the Silverado. That means no shoehorning, and thus no compromises that might result in reduced efficiency.
Beyond designing the engine to run efficiently, it's largely constructed from aluminum to save weight. Components made from the lightweight metal include the block, head, and lower crankcase extension.
The turbocharger has variable geometry, meaning it can close and open its vanes depending on load. It's also controlled electrically rather than vacuum-controlled, meaning the vehicle's computer can further optimize its performance. Chevrolet also used roller bearings which allow it to spin up to 175,000 rpm and boost up to 29 PSI.
GM-Designed Combustion Chamber
As part of its ground-up design, the 3.0-liter unit features a combustion chamber designed in-house by GM. Verdino told us, "the efficiency of the engine starts from the energy you put into it, so you have to efficiently burn the fuel." He added, "you have to drive the fluids in an efficient way because that is energy subtracted from the engine, the combustion, and the wheels." The exact methodology used to craft the chamber is a corporate secret, but it's critical. Trust us.
Chevrolet maximized its control of engine temperature with a number of special inclusions. A flow-control valve can stop the flow of water altogether, meaning that when conditions are too cool, engine temperature can be increased.
A rotary valve allows control of water to several different areas. Barta said, "There's three ball valves in there which allow us to control the water to several different areas. We have split cooling—one to the head, one to the block." He added, "We also have a separate circuit that goes to the transmission oil cooler, a separate circuit which goes to our engine oil cooler. We have a separate one that goes to the cabin heating." Essentially, the engineering team has developed an engine that can very precisely regulate its temperature, allowing it to operate at peak efficiency more of the time.