Auto Service World
Feature   January 1, 2001   by CARS Magazine

2001 GM Heavy Duty Pickups

More power, more pickup


Can you ever have too much power in a pickup? The traditional answer is “No”, and GM appears to have raised the bar in the horsepower wars with a major revamp of powerplants and the chassis they power with the launch of the 2001 Silverado and Sierra HD models. Of course “HD” stands for “heavy duty”, and the much overused phrase is legitimately applied to the new 3/4 and one-ton trucks. The major news is in the powertrains, where three new engines offer very high levels of horsepower and usable torque. The 6.0L Vortec 6000 V-8 generates 300 hp at 4400 RPM, and 360 lb.-ft of torque at 4000 RPM. The boost over the previous 5.7L V-8 comes courtesy of cast aluminum heads patterned after Corvette castings, changes to the cam profile, and true dual exhausts for minimum back pressure. The engine features a “limp home mode” which allows reduced power operation after a total coolant loss, and an engine oil life monitor. Despite the power boost, the new engine is more fuel-efficient than the previous generation, and is designed for 320,000-km operation without a major component failure. The “big block” has also been redesigned, and now displaces 8.1 L, with a peak output of 340 hp at 4200 RPM and a diesel-like 455 lb.-ft of torque at 3200 RPM. Four bolt mains support the internally balanced nodular iron crank, which swings Teflon-coated low friction pistons. Newly designed heads clamp to the block with five bolts per cylinder, and head gaskets are 1.3 mm thicker. Crankcase ventilation is by cast-in internal passages, eliminating PCV plumbing, and exhaust manifolds are now stainless steel. Valves operate by hydraulic roller lifters on a steel camshaft. Ignition is by a coil-near-plug system that boosts ignition energy by 50 percent. Controlled-compression gaskets under the valve covers, oil pan and intake manifold improves sealing, and a dual-belt accessory drive system isolates the A/C compressor from the other accessories. The dual system, combined with a new belt material, extends belt life to 240,000 km. The throttle is electronically controlled by actuators which combine throttle, cruise control, and traction control in a single unit. The mass airflow sensor uses an integral temperature sensor, and the fuel injection system operates at a relatively high 400kPa for rapid cold starts. Even the firing order has been changed to 1-8-7-2-6-5-4-3 to reduce main bearing wear. Fuel economy of the Vortec 8100 is actually four percent better than the 2000-model 6.5-L diesel.

That 6.5 diesel has itself been replaced by a new Duramax 6600 turbo V-8 unit producing 300 hp at 3100 RPM and a huge 520 lb.-ft of torque at 1800 RPM. The high output comes through a deep-skirt aluminum block with induction hardened cylinder bores, a nitrided forged steel crank clamped by side bolted main bearing caps, and a full bellhousing. The valvetrain is OHV, with four valves per cylinder. Cold-cracked connecting rods, roller cam followers and a cam that is gear-driven give the Duramax unit 320,000-km durability. The common-rail high-pressure injection system is by Bosch, and the water pump is gear-driven. There’s enough new and improved about the new powerplants to justify an article on engines alone, but transmissions and chassis are also upgraded on the 2001 Silverado/Sierra twins. The German-built ZF S6-650 six-speed manual unit features a super-low “creeper” first gear for trailering or plowing, with reverse positioned straight back from first for easy parking lot maneuvering. The new ‘box uses a stiff integral bellhousing and is “lubed for life” with synthetic oil. A PTO allows mounting of hydraulic pumps of up to 25 hp on 3500-series models.

The new automatic is Allison’s “1000” five-speed. It’s similar to commercial truck designs and has fully electronic control of shifting. The unit features a “Tow-Haul” mode which locks the converter in second, third, fourth and fifth gears to reduce heat buildup, and a shift stabilization system to prevent the transmission from “hunting” during hill-climb and heavy hauling. The electronic control through the Transmission Control Module also allows engine braking on steep hills by sensing load weight, vehicle speed and deceleration rate to automatically downshift through the gears, saving wear on the brakes. Even the parking pawl is rated at 9000kg (19,850lbs) and like the ZF manual, features a PTO on one-ton models. Other transmissions in the series include a New Venture Gear five-speed manual, and a GM 4L80-E electronically controlled automatic with overdrive, which also contains a Tow-Haul mode.

The chassis underneath the advanced powertrains features a bussed electrical system with 96 percent fewer splices and 23 percent fewer wires, as well as battery rundown protection. Suspension is now by torsion bars and multi-stage leaf springs, and frames use a combination of hydroforming and high-strength low alloy (HSLA) steel for greater strength. All steering joints are equipped with grease fittings, and the new four-wheel disc brakes are assisted by GM’s Hydro-Boost system. Brake pad life is double that of previous models, and the parking brake can hold a fully loaded truck on a 30 percent grade with the transmission in neutral.

The states are impressive, but how does the new design work behind the wheel? SSGM spent a day wandering Alberta at the wheel of a one-ton “dually” with the Duramax diesel and Allison automatic, pulling a loaded triple axle construction trailer, and a thousand pounds of sandbags in the box. The Foothills offered some long, steep grades, and the truck demonstrated excellent acceleration, as might be expected with over 500 ft-lbs. of torque. The engine grade-braking feature works well, although it seems strange to haul down from speed going downhill without significant use of the wide pedal. The machine is also capable of speeds in excess of 160km/h (without trailer, of course) suggesting that gear ratios are wide enough for comfortable daily use. The Silverado/Sierra heavy-duty pickups are comfortable, well built and are optimized for heavy use, so if your operation has to combine hauling, with plowing and daily driving or commuting, these trucks should be a satisfying drive. SSGM


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