In 1997, Isuzu Motors Ltd. and General Motors created DMAX Ltd., a joint venture for producing diesel engines. The Duramax 6600 was the first engine that came into fruition after this relationship started.
The LB7 Duramax diesel is a direct-injected, turbocharged, intercooled, four-valve-per-cylinder V-8 that produces 300 hp and 560 lb-ft of torque. Starting from a blank sheet of paper, the 6.6L Duramax is recognized to date as the fastest diesel development program in the world.
It went from concept to initial production in only 37 months. This included the construction of a brand-new "green field" manufacturing plant in Moraine, Ohio. The 600,000 square-foot facility resides on 40 acres and includes four machining lines, a heat-treat facility, and engine assembly. In addition, machining of the cylinder blocks, cylinder heads, crankshafts, and connecting rods are accomplished in Moraine. The factory currently has capacity to produce 105,000 engines per year.
Duramax production of the LB7 engine began in the summer of 2000, and the project was a collaboration of engineering talent from GM and Isuzu-each taking the lead in their respective area of expertise.
Size Matters
Gasoline engines had dominated the fullsize pickup class, so General Motors' goal was to design a diesel engine that would take up no more space than the gasoline engine it would replace as an option. Because a diesel requires additional equipment-such as a turbocharger, injection pump, and intercooler-this needed to be acknowledged during the early stages of development. Due to this requirement, the architecture of the engine would include the following: the turbocharger, fuel-injection pump, and fuel rails that would be installed in the valley of the engine block for a smaller engine profile. The oil cooler was directly attached to the left side of the cylinder block. Coolant would be distributed to the left and right banks through a water passage in the flywheel housing. This simplified the coolant piping and would also increase reliability by facilitating even temperatures for both sides of the engine.
Auxiliary equipment-such as the air conditioner compressor, the power-steering pump, and the alternator-would be driven by one serpentine belt. The mounting brackets for the accessories would be located on the front surface of the engine for ease of in-field service and assembly plant installation
Engine Block
The rigidity of the cylinder block was a concern not only for durability but for noise suppression as well. This was accomplished with a deep-skirt cylinder block structure and by connecting the bearing caps to the lower part of the block with side bolts, in addition to the two main bolts. The Duramax block is manufactured from a special gray iron alloy.
The upper portion of the block is a closed-type and has a structure designed for minimal deformation at the high combustion pressure of a diesel engine. Another goal was to decrease the lower portion of the engine's width.
Minimizing bore distortion was important for maintaining the piston rings' sealing performance and to ward off engine seizure. This was done by evenly positioning six cylinder-head bolts around each bore by evenly distributing coolant around each independent cylinder and arranging cooling water holes on the cylinder-head deck surface. The six head bolts around each cylinder also help the gasket withstand the high in-cylinder pressure of a direct-injection, turbocharged engine. The upper portion of the linerless cylinder bore is induction hardened to reduce wear.
Cylinder Heads
The cylinder head is made of gravity-cast aluminum and has a four-valve design for good volumetric efficiency and blowdown during the exhaust cycle. The fuel injector is located in the center of the combustion chamber along the cylinder line. A stainless sleeve is pressed into the cylinder head, and the fuel injector is inserted in it. The arrangement of the valves is categorized as a "twist type." This describes the two independent intake ports that are designed to maximize tangential flow for optimum intake swirl.
Adequate and even cooling of the valve seats greatly contributes to minimizing any change in the valve lash. There is a large space between the valve seats that uses the cooling ability of aluminum to reduce the heat deformation. An aluminum cylinder head has higher heat conductivity, so it has a lower temperature on the surface of the combustion chamber when compared to a cast-iron design. With a cast-iron test cylinder head, the exhaust valve seat temperature was 608-662 degrees Fahrenheit. With the aluminum cylinder head, which also benefited from a larger space between the valves, the temperature was maintained at 428 degrees or less. The lower temperature enhances durability of the valve seats and increases reliability of the engine as a whole
Head Gaskets
The head gasket has a steel laminate structure composed of three stainless steel plates (each plate is fluorine coated). Steel laminate deteriorates very little over time and is highly heat resistant, so it can withstand high in-cylinder pressure.