GMC has announced details on the new Duramax 6.6-liter V8 turbo-diesel to be offered on the 2017 Sierra HD. The new engine represents a complete redesign and will deliver more horsepower and torque than prior generations. The new Duramax will be built at the GM manufacturing facility in Moraine, Ohio.
GMC states that the new engine will achieve an SAE-certified 445 horsepower and net 910 pound-feet of torque. The new engine represents a 19 percent increase in net torque over the current generation Duramax, with 90 percent of peak torque available at 1,550 rpm and peak torque at 1600 RPM. Peak torque is sustained up to 2,850 rpm.
“Nearly everything about the Duramax is new, designed to produce more torque at lower rpm and more confidence when trailering or hauling,” says Gary Arvan, chief engineer.
GMC also states that the redesigned engine will be both quieter and smoother than the current generation. According to GMC, engine noise at idle is reduced by 38 percent.
“You’ll notice the refinement improvements the moment you start the engine and appreciate them as you cruise quietly down the highway — with or without a trailer,” Arvan says.
An All-New Design
Only the bore and stroke dimensions of the current Duramax engine have been retained in the redesign. Similar to previous Duramax designs, the new engine block is made from a strong cast-iron alloy known for its durability, with induction-hardened cylinder walls and five separate four-bolt main bearings. The cylinder bore has been maintained at 4.05-inches, with a 3.89-inch stroke. These are the same dimensions as the current Duramax, yielding 6.6-liter or 403 cubic inch displacement.
The new engine block incorporates larger-diameter crankshaft connecting rod journals than the current engine, enabling the use of a stronger crankshaft and increased the bearing area to handle higher cylinder loads.
The connecting rods are stronger, too, and incorporate a new 45-degree split-angle design to allow the larger-diameter rod bearings to pass through the cylinder bores during engine assembly. They’re forged and sintered with a durable powdered metal alloy, with a fractured cap design enabling more precise cap-to-rod fitment.
A new, stronger cast aluminum piston design tops off the rotating assembly with a segment first for Duramax. Each piston features a taller crown area and a remelted combustion bowl rim for greater strength. Remelting is an additional manufacturing process for aluminum pistons in which the bowl rim area is reheated after casting and pre-machining, creating a much finer and more consistent metal grain structure that greatly enhances thermal fatigue properties.
The Duramax best-in-class aluminum cylinder head has been revised and upgraded, with six head bolts per cylinder and four valves per cylinder. The aluminum construction helps reduce the engine’s overall weight, while the six-bolt design provides exceptional head-clamping strength, which is absolutely critical in a high-compression, turbocharged diesel application.
A new aluminum head casting uses a new double-layer water core design that separates and arranges water cores in layers to create a stiffer head structure with more precise coolant flow control. The heads’ airflow passages are also heavily revised to enhance airflow, contributing to the engine’s increased horsepower and torque.
An enhanced oiling circuit, with higher flow capacity and a dedicated feed for the turbocharger, provides increased pressure at the turbo and faster oil delivery. Larger piston-cooling oil jets at the bottom of the cylinder bores spray up to twice the amount of engine oil into oil galleries under the crown of the pistons, contributing to lower engine temperature and greater durability. The new engine also features an integrated oil cooler with 50 percent greater capacity than the current Duramax.
New Engine Management and Biodiesel Capability
In addition to the stronger engine design, GM has developed an all-new engine management system to monitor and control operations. The new Duramax employs a common-rail direct injection fuel system with new high-capability solenoid-type injectors. High fuel pressure of 29,000 psi (2,000 bar) promotes excellent fuel atomization for a cleaner burn that promotes reduced particulate emissions.
The new injectors also support up to seven fuel delivery events per combustion event, contributing to lower noise, greater efficiency, and lower emissions. Technology advancements enable less-complex solenoid injectors to deliver comparable performance to piezo-type injectors.
A new electronically controlled, variable-vane turbocharger advances the Duramax’s legacy of variable-geometry boosting. Compared to the current engine, the system produces higher maximum boost pressure — 28 psi — to help the engine make more power, and revisions to enhance the capability of the exhaust-brake system.
As a side benefit, the new Duramax is officially certified to use biodiesel in concentrations up to B20. As the name suggests, B20 is composed of 20 percent biodiesel and 80 percent conventional diesel. B20 helps reduce carbon dioxide emissions and dependence on fossil petroleum. It is a domestically produced, renewable fuel made primarily of plant matter — mostly soybean oil.
Allison 1000 Automatic Transmission
Also announced as the partner to the new Duramax engine is the proven Allison 1000 six-speed automatic transmission. Several improvements have been made to accommodate the new engine’s higher torque capacity, including a new torque converter.
The Allison 1000’s technologically advanced control features, such as driver shift control with manual shift feature and a patented elevated idle mode cab warm-up feature, have not changed. Also, the Tow/Haul mode reduces shift cycling for better control and improved cooling when towing or hauling heavy loads. The transmission is also set up for the Duramax exhaust brake on the Sierra HD.