The Diesel Page

Originally published December 19, 1999, this was among the very first public announcements made by General Motors for their brand new Duramax 6600 diesel engine. This announcement was made 2 months after The Diesel Page was included in the first-ever hands-on performance test of a pair of GMC and Chevrolet 2500HD prototype pickups equipped with the new Duramax and Allison. Editorial coverage of this engine and GM's pickup trucks began right here in The Diesel Page.

New Duramax Diesel 6600 to Help GM Heavy-Duty Pickups and Chassis-Cabs Set New Industry Benchmarks in 2001 Model Year

DETROIT, Dec. 15 /PRNewswire/ -- An all-new Duramax Diesel 6600 engine will debut as an optional engine in GM's 2001 Chevy Silverado and GMC Sierra 2500HD/3500 pickups, Crew Cabs, Big Dooley and Chassis-Cab models, next year. It is positioned to help GM set new industry standards for diesel power, performance, durability/reliability and quiet operation in the growing heavy-duty (HD) pickup class.

The new Duramax Diesel 6600 is the product of a joint venture (DMAX Ltd.) between GM and Isuzu Motors, and it's the second in a growing family of GM-branded Duramax engines. The first was the Duramax 7800 (7.8-liter) engine, which became available in the 2000 model year of GM medium-duty truck models earlier this year.

GM's relationship with Isuzu began in 1971 and was strengthened in 1997 when GM announced that Isuzu would develop diesel engines for GM. Because of Isuzu's expertise in commercial vehicles and diesel engines, the company plays an important role in GM's global strategy. They have produced and sold more than 60 million diesel engines over the past six decades, and they enjoy a solid reputation for reliable and dependable performance. This expertise is being counted upon to help GM establish a dominant position in the diesel- powered full-size truck market just as the Vortec family of gasoline engines has done.

Duramax Diesel engines will be sourced and manufactured through a brand new manufacturing facility in Moraine, Ohio.

Duramax Diesel 6600 Availability

The new Duramax Diesel 6600 will be available as optional equipment on 2001 Chevy Silverado and GMC Sierra 2500HD/3500 Series pickups, including Crew Cab, Big Dooley and Chassis-Cab models. These new trucks are scheduled to debut during the fall of 2000.

When specified, the Duramax will be mated to either a ZF 6-speed manual transmission (std), or an all-new 1000 Series(TM) 5-speed automatic transmission (opt) from Allison Transmission.

Additional Duramax 6600 applications are planned for other GM truck products, and announcements regarding those will be at an appropriate time in the future.

Duramax Diesel 6600 Features and Advantages

Totally new, 90-degree, direct-injection, overhead valve (OHV) four-valve- per-cylinder turbocharged diesel V8, with aluminum high swirl cylinder heads and significantly improved cooling characteristics.

The Duramax 6600's four-valve-per-cylinder configuration is the standard for modern diesel engine design. It optimizes airflow in and out of the engine, improves breathing at higher rpm's, processes more air and, therefore, generates more horsepower than competing designs.

The Duramax 6600 has a slight twist to the shape of its valves relative to the centerline of the crankshaft. This gives incoming air some added swirl, which is important in the combustion process to controlling emissions and maximizing fuel efficiency.

To further maximize efficiency, the Duramax 6600 incorporates a number of cooling techniques:

Charge air cooler. The center-mounted turbocharger on the Duramax pulls fresh ambient air in through the air cleaner and into its compressor. After being compressed, the air is then channeled through a duct to the charge air cooler (which is packaged like an additional radiator in front of the water radiator). The cooled air then travels through the intake manifold and into the engine. This cooler air is denser, so it provides more power. A secondary result is reduced combustion chamber temperatures ... a major factor in GM's extended engine durability strategy.

Integral oil cooler. The Duramax's integral oil cooler is like those found on many medium-duty truck engines. Instead of being located in the radiator end tank, it is mounted on the side of the engine. All of the water flow from the gear-driven water pump is channeled through the oil cooler before it goes through the engine. The result is increased oil cooling and extended engine life.

Piston spray cooling. Pistons have to absorb the full shock of thermal loads and high combustion pressures -- both of which are much stronger in diesel engines than those found in the typical gasoline engine. For that reason, the Duramax has a piston spray cooling system that sprays oil directly onto the backside of each piston bowl. The added cooling that this system provides adds to reliability and durability.

Transmission oil cooler. This new transmission oil cooler, used with the Allison 1000 5-speed automatic transmission, is mounted below the radiator to preclude heat from the transmission going into the engine cooling system. It relies on RAM air from openings in the front bumper. The size of the cooler has been increased from previous models, and its larger 5/8-inch lines (compared to 3/8-inch lines previously used) provide for a very liberal 6-gallon-per-minute (GPM) transmission fluid flow rate. Transmission fluid cooling is substantially improved as a result.

Larger 21-inch-diameter composite fan with larger modulating clutch and a 2-piece fan shroud. The benefits of a larger fan are almost too obvious to mention ... it simply pulls more air through the radiator. The larger modulating fan clutch reduces fan noise, and the 2-piece fan shroud allows for easy service.

Best-in-class power/performance with the segment's highest horsepower and peak torque ratings. Targeted ratings are 300 horsepower @ 3,100 rpm and 520 lb-ft of torque @ 1,800 rpm. Its high, flat torque curve will deliver more power across the power band than any competitor, and will help Duramax 6600- equipped GM HD pickups excel in off-the-line performance, acceleration and heavy-duty trailering and hauling.

Best-in-class durability and reliability. The Duramax 6600 has a targeted operating life of at least 200,000 miles without any major component failures. Key durability enhancements, in addition to all of the enhanced cooling features previously mentioned, include:

A nitrided crankshaft. Nitriding has proven to be one of the most effective methods of guaranteeing crankshaft dependability over time.

A deep-skirt block design, with side-bolted main bearing caps for increased strength and structural rigidity. The deep-skirt design was optimized using Finite Element Analysis (FEA) to enhance engine balance, make the structure more rigid, and provide smoother, quieter engine and driveline operation.

An induction hardened block. It's an exclusive for diesel engines in this class.

Hardened valve seat inserts in the aluminum cylinder heads. Another exclusive for engines in this class, they provide better durability and reliability, as well as improved serviceability.

A gear-driven water pump with metal gears for more robustness is another new feature that's common to medium-duty truck engines. In most engines, the water pump is driven by the fan belt. This gear-driven design reduces stress on the accessory drive belt, and it also means that a customer will not be stranded if the drive belt fails.

Significantly improved fuel economy. Duramax 6600 engines will be much more efficient than previous GM Diesels. They offer significantly improved fuel economy (specific fuel economy is 15-20 percent better than GM's current 6.5 turbo diesel, for instance), particularly at highway speeds. This big improvement in fuel efficiency was principally achieved with:

The engine's new lightweight design. The Duramax 6600 weighs only 836 lbs. (379 kg) thanks to the use of aluminum in key components like the cylinder heads, crankcase, accessory drive brackets, intake manifold and flywheel bell housing.

The engine's new Bosch direct-injection, common-rail fuel system, which provides maximum power for each pulse of fuel used.

Best-in-class operating quietness and smoothness. The new Duramax 6600 posts noise, vibration, and harshness (NVH) figures more typical of similar- sized gasoline engine. This astounding improvement is due to many of the structural enhancements previously mentioned (deep-skirt block design, casehardening of the block, one-piece aluminum crankcase and one-piece aluminum bell housing), as well as the Bosch electrically-controlled fuel- injection system which allows full authority in injection timing and quantity.

Easy serviceability, created in part by:

The engine's compact size. It's shorter and narrower than any of the competitors' diesel engines, allowing for easier access to external components. For instance, the Duramax is 34.5 in. long (878mm), compared to Ford's at 35.2 in. (896mm) and Dodge's at 38 in. (967mm).

The placement of the turbocharger in the "V" space atop the engine. This space is normally not used by competitors, despite the fact that it allows for better packaging efficiency.

The thoughtful placement of items such as: the timing gear chain (located at the front of the engine), an easier-access oil filter (located at the lower right rear corner of the engine) and the fuel filter (located at the upper right rear of the engine). All are easily accessible and reduce service time.

Duramax Diesel 6600 Fuel Delivery System

The direct-injection fuel system on the Duramax 6600 has been mentioned several times in previous paragraphs. However it is different enough from other direct-injection systems that it is worth talking about in more detail. The system was developed by Robert Bosch Corp., the industry leader in diesel fuel-injection systems.

Direct-injection means the injector sprays fuel directly into the combustion chamber, which allows for more efficient combustion. In addition, the electronic common-rail system adds a new dimension to diesel fuel control over its mechanical predecessors. For the first time, pressure generation is decoupled from and independent of engine speed and the injection event. Engineers can now program the system for optimal performance over the entire engine speed range, and achieve new levels of economy, emissions and driving comfort under all conditions. What makes the Duramax 6600's fuel delivery system better than most other systems is the strategy and technology used to deliver fuel to the injectors ...

The fuel is drawn from the tank by the low-pressure pump through the Electronic Driver Unit (EDU). The fuel cools the electronics, which have the arduous task of actuating the solenoid valves in each injector, sometimes over 25 times per second! The EDU works in concert with the Engine Control Module

(ECM) to provide a strong, precise signal for each cylinder's combustion event. The EDU also controls pressure in the fuel rail to ensure that it will be correct for precise fuel metering.

From the EDU, the fuel passes through an engine mounted fuel filter. This filter has a water sensor, a water separator and a fuel heater. If necessary, the heater warms the fuel to 14 degrees C to prevent any waxing of the fuel.

The fuel then goes to the Bosch high-pressure pump. If the ECM and EDU are the brains of the system, the Bosch high-pressure pump is clearly the heart. It sends the fuel to the fuel rails, variably controlled at pressures up to 23,000 psi, where it is distributed to the injectors at each cylinder.

The injector, with a constant injection pressure fed to it, can now open, stay open and close as directed by the ECM and EDU, depending on various sensor inputs, to achieve effective combustion for the conditions present. The injector is optimally located in the cylinder head, and configured with a custom-designed spray pattern matching the combustion chamber, to gain most efficient combustion. This in turn enables improved fuel economy, lower emissions and less heat loss and rejection.

The sophistication and technology of the system components make the Duramax capable of employing a process known as "pilot injection."

Pilot injection involves injecting a small amount of fuel into the cylinder prior to the main injection event. A complex process in the electronic controls selects the optimal time, duration and quantity of pilot injection, coupled with the main injection charges. As a result, combustion starts on a smaller scale and builds subtly but rapidly for reduced noise/knock, less vibration and quieter, smoother warm-ups.

Summing It All Up:

GM's current benchmark status in full-size pickups, Isuzu's in diesel engines, Bosch's in fuel injection and Allison Transmission's in commercial- duty automatic transmissions all combine to ensure that next year GM's Duramax Diesel-powered HD pickups will achieve benchmark status in the full-size diesel pickup segment.

Basic Specifications: Duramax Diesel 6600 vs. The Competition

                    Chevy/GMC                 Ford                     Dodge
--------------------(Duramax 6600) ----------(Navistar T444)----------(Cummins ISB)------

Engine Description: OHV-4-valve-V8            OHV-2-valve-V8         OHV-4-valve-L6
Bore x Stroke        4 x 3.89                 4.1 x 4.2              4 x 4.7
Displacement (liters) 6.6                     7.27                   5.88
Bore Pitch (inches)   4.6                     4.8                    4.7
Maximum Power (hp)  300 @ 3100 rpm            235 @ 2700 rpm         235 @ 2500 rpm
Torque (lb-ft)      520 @ 1800 rpm            500 @ 1600 rpm         460 @ 1600 rpm
Combustion System   DI Diesel                 DI Diesel              DI Diesel
Air Intake System   TC air-cooled             TC air-cooled          TC air-cooled
Timing Train        Gear                      Gear                   Gear
Injection System    Bosch common rail         CAT HEUI               Bosch VP44
Piston Cooling      Oil spray                 Oil spray              Oil spray
Oil Cooler          Integral to engine        Integral to engine     Integral to engine

SOURCE Chevrolet Motor Division

CO: General Motors Corporation; Chevrolet Motor Division; Isuzu Motors; Robert Bosch Corp.; Allison Transmission
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