GM expands power, torque
Nov 1, 2007 12:00 PM, By Rick Weber
For 2008, General Motors' TopKick models offer more power, more torque, six-speed Allison transmissions on most models, and other enhancements.
Mike Eaves, product manager for medium-duty trucks, said that while the displacement specs match those of the previous version, the available Duramax 6.6-liter V-8 turbo-diesel powering the 2008 TopKick differs greatly from its predecessor:
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GMC C8500 TopKick is available this year with horsepower ratings up to 300 hp.
New fuel injectors to precisely control combustion.
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More durable variable-geometry turbocharger. The compressor is changed to a “boreless” type, increasing durability at high RPM.
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A larger exhaust gas recirculation chamber to help control combustion temperatures, contributing to lower emissions.
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A closed crankcase ventilation system. The crankcase ventilation system is a sealed chamber between both cylinder banks to ensure that emissions from the crankcase are kept to a minimum.
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A diesel particulate filter (DPF) system. To reduce particulate matter, the ceramic honeycomb channel DPF captures sulfate particles and soot. Exhaust gases are directed through the channels and through a porous material that traps the particulates.
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An intake throttle for precise combustion temperature control increases the amount of load on the engine during low-load conditions, such as idling for extended periods and unladen low-speed driving. The throttle is operated by the engine control module (ECM) as an additional control for combustion temperatures
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An electrically variable engine cooling fan. The engine cooling fan is now controlled by the ECM, allowing the engine cooling system to be assisted by the fan only when necessary. This results in more precise control over the engine temperature.
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Increased engine control processing. The E35 ECM now controls the new injectors, the data from the diesel particulate filter pressure sensors, the new intake throttle operation, and the electrically variable engine cooling fan.
The new Duramax 6.6L is available in two horsepower and torque configurations: 300 horsepower at 3000 rpm and 520 lb-ft at 1600 rpm; and 330 hp at 3000 rpm and 620 lb-ft of torque at 1600 rpm.
The standard engine in C4500 and C5500 models is the Vortec 8.1L gasoline V-8, which delivers 325 hp at 4000 rpm and 450 lb-ft of torque at 2800 rpm.
C6500, C7500, and C8500 models are powered by one of three engines: a Vortec MD (8.1L V-8) delivering 295 hp and 440 lb-ft of torque; an Isuzu 6H (7.8L diesel I-6) delivering horsepower ranges from 215 to 300 and torque ratings from 560 to 860 lb-ft; and a Caterpillar C7 (7.2L diesel I-6) with horsepower ratings from 207 to 250 and torque ratings from 520 to 800 lb-ft.
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