PONTIAC, MICH. - GM's Duramax 6600 6.6L turbo-diesel V-8 engine will provide higher power and torque ratings and major emission improvements beginning in January 2004.

Silverado and Sierra 2500HD and 3500 Series trucks with the Duramax 6600 and the Allison automatic transmission will receive a new version of the engine with 310 hp @ 3100 rpm, 10 more horsepower than before. The engine also features a higher torque rating of 590 lb-ft @ 1600 rpm, a 70 lb-ft increase over its previous maximum high. At the same time, Duramax 6600 NOx emissions have been reduced almost by half.

"Since its introduction in 2001, the Duramax 6600 has re-established GM in the full-size diesel powered truck market by increasing our share of the segment to nearly 30 percent," said Charlie Freese, executive director, diesel engineering for GM Powertrain.

Silverado and Sierra models with the Duramax 6600 and a standard ZF S6-650 six-speed manual transmission receive the same emissions improvements as those with the Allison 1000, with carryover power ratings.

"Over 90 percent of our three-quarter and one-ton customers order their Duramax 6600 with the Allison 1000 five-speed automatic transmission - prompting us to focus on power, torque and emissions improvements, where they provide greatest benefits for the largest number of customers," Freese said.

Both the new version of the Duramax 6600 turbo diesel with the Allison automatic transmission and the version with the standard ZF six-speed manual feature improved hardware. The new version also has additional software calibration changes to help provide its higher power output.

Primary hardware changes include a variable nozzle turbocharger, new electronic control module, next-generation fuel injectors, electronically controlled cooled exhaust gas recirculation (EGR), 50 state catalytic converter usage, improved charge air-cooling and a closed crankcase ventilation system:

The common rail fuel system also uses smaller, more precisely machined and positioned next-generation fuel injectors to inject its fuel pulses into the cylinders. The injectors are now fully accessible, allowing service technicians to access them without having to take the cylinder head cover off. Servicing is typically required only every 100,000 miles or more.

The new variable nozzle turbocharger features vanes that are now hydraulically controlled to precisely adjust the level of boost generated by the turbocharger.

A more powerful, 32-bit, next-generation engine control module provides the capabilities for integrated control of the additional engine hardware. The new engine controller provides faster microprocessor speeds, increased throughput and more memory than the previous generation controller.

The EGR system in conjunction with catalytic converter usage reduces NOx emissions in all 50 states to approximately 2 grams per brake horsepower hour from a previous 4 grams in 49 states and 3.5 grams in California.

Charge-air cooling is used to provide cool dense air to the cylinders to help generate the new engine's increased power, torque and improved emissions.

The closed-crankcase ventilation system, although not required to meet 2004 emissions regulations, anticipates upcoming 2006-model emissions requirements by incorporating a closed crankcase ventilation system in which harmful vapors are vented internally and burned as part of the combustion process, rather than being vented to the outside atmosphere.

"The engine's high torque across the power band helps Duramax 6600-equipped GM trucks excel in off-the-line performance, acceleration and heavy-duty trailering and hauling," Freese said.

New versions of the Duramax 6600 will be produced at GM's Moraine, Ohio facility. The engine was developed through a GM and Isuzu Motors joint ventures (DMAX Ltd. and GMIDEL).

GM Powertrain is a global producer of engines, transmissions, castings and components for GM vehicles and other automotive, marine, and industrial OEMs. Headquartered in Pontiac, GM Powertrain has operating and coordinating responsibility for General Motors powertrain manufacturing plants and engineering centers in North America, South America, Europe, and the Asia-Pacific region.