GMC has announced a redesigned Duramax 6.6-liter V8 turbo-diesel is to be offered in its 2017 Sierra HD models. The redesigned engine offers an SAE-certified 445hp and 910lb.-ft. (1,234Nm), which GMC states ‘enables easier, more confident hauling and trailering’.
Along with a 19% increase in max torque over the current Duramax 6.6L, the redesigned turbo-diesel’s performance is said to be significantly quieter and smoother, for greater refinement with engine noise at idle reduced by 38%.
A new, patent-pending vehicle air intake system has been implimented to achieve cooler engine temperatures during difficult conditions such as trailering on steep grades. GMC states that the intake design is another example of the ‘advanced integration’ included in the 2017 Sierra HD that makes it ‘over-the-road capable’.
As with previous versions, the new Duramax block features a cast-iron foundation, with induction-hardened cylinder walls and five nodular iron main bearings. It retains the same 4.05-inch (103mm) and 3.89-inch (99mm) bore and stroke dimensions as the current engine, allowing it to also retain the Duramax’s familiar 6.6L (403cu.-in./6,599cc) displacement.
A deep-skirt design and four-bolt, cross-bolted main caps help ensure the block’s strength and enable more accurate location of the rotating assembly. A die-cast aluminum lower crankcase also strengthens the engine block and serves as the lower engine cover, while reducing its overall weight.
The new engine block incorporates larger-diameter crankshaft connecting rod journals than the current engine, enabling the placement of a stronger crankshaft and increased bearing area to handle higher cylinder loads.
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.
GMC states that the addition of a new, two-piece oil pan contributes to the new Duramax’s quieter operation. It consists of a laminated steel oil pan with an upper aluminum section. The aluminum section provides strength-enhancing rigidity for the engine, but a pan made entirely of aluminum would radiate more noise, so the laminated steel lower section is added to dampen noise and vibration.
The new oil cooler has a 50% greater capacity than the current engine’s, ensuring more consistent temperatures at higher engine loads.
A tough, forged micro-alloy steel crankshaft anchors the new Duramax’s stronger rotating assembly. Cut-then-rolled journal fillets contribute to its durability by strengthening the junction where the journals the round sections on which the bearings slide meet the webs that separate the main and rod journals.
The connecting rods are now forged and sintered too, and incorporate a new 45° split-angle design to allow the larger-diameter rod bearings to pass through the cylinder bores during engine assembly. A new, stronger cast aluminum piston design tops off the rotating assembly. It features a taller crown area and a remelted combustion bowl rim for greater strength.
The redesigned engine retains the previous-generation’s aluminum cylinder head design, 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 the required head-clamping strength for a high-compression, turbocharged 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.
The Duramax employs a common-rail direct injection fuel system with new high-capability solenoid-type injectors. High fuel pressure of 29,000psi (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 28psi (195kPa) to help the engine make more power, and revisions to enhance the capability of the exhaust-brake system.
The new Duramax 6.6L is capable of running on B20 biodiesel, a fuel composed of 20% biodiesel and 80% conventional diesel. B20 helps lower carbon dioxide emissions and lessens dependence on petroleum. It is a domestically produced, renewable fuel made primarily of plant matter mostly soybean oil.