The Heavy Duty Chevy and GMC Pickups
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After months of speculation through rumors, concept vehicles, and even our own exclusive road test of the new 6.6L Duramax turbodiesel, GM invited us to Detroit in mid-December for a sneak peek at the redesigned Chevy and GMC heavy-duty pickups.
Possibly the most salivating of topics for big-truck enthusiasts is engine power. And with a redesigned 6.0L V-8 (Vortec 6000) as the standard engine, an optional new 8.1L big-block V-8 (Vortec 8100), and a 6.6L turbo-diesel V-8 (Duramax 6600), these pickups are poised to deliver. The standard Vortec 6000 V-8 receives aluminum heads, a new cam, and lower-restriction exhaust this year and will produce 325 hp and 370 lb-ft of torque in the new 2500HD and 3500 trucks.
The new Vortec 8100 will trump Ford and Dodge's V-10s in both power and torque with a target output of 340 hp at 4,200 rpm and a whopping 455 lb-ft of torque at 3,200 rpm. This was achieved by basically stroking the Vortec 7400 (known by most as the big-block 454) to a total stroke length of 4.37 inches, introducing coil-on-plug ignition, an internally balanced crankshaft, a new firing order, redesigned ports on the heads, even-length intake runners on the intake manifold with an integrated fuel-rail system, pistons with a shorter combustion height and tighter rings, and stainless steel exhaust manifolds. The new Isuzu-built Duramax diesel will also outpower its competitors by producing 300 hp at 3,100 rpm and a trailer-yanking 520 lb-ft of torque at 1,800 rpm.
Connected to these new powerplants are two new transmissions and a revised 4L80E four-speed automatic. The standard Vortec 6000 will be mated to the 4L80E, while the Vortec 8100 and the Duramax will use either the new five-speed Allison 1000 automatic transmission or a ZF-built S6-650 six-speed manual. The Allison 1000 is quite sophisticated and can handle GVWRs (gross vehicle weight ratings) up to 19,850 pounds and GCWR (gross combined weight ratings) up to 26,000 pounds. It comes with PTO capability and, among other features, Grade Braking.
Allison's Grade Braking feature uses a multitude of inputs gathered by the computer to calculate shift parameters. This means the tranny should downshift on a long grade to slow a load, acting similarly to an exhaust brake or an engine brake on the larger trucks.
The ZF six-speed manual is the same basic unit Ford uses in its Super Duty pickups, however the GM version uses an integral bellhousing and a dual mass flywheel for better shift quality. According to a GM source, the NVG 5600 six-speed was not used, because the ZF box provides a weight-savings of more than 100 pounds with similar torque-handling capability.
Quite honestly, we had hoped these trucks would have a solid-front-axle design on 4WD models. However, it seems GM is committed to the IFS (independent front suspension) design used on current trucks. Although no 4WD models were present for our viewing, we can expect the design to look like a beefed-up version of the 1500 and light-duty 2500-series trucks currently in production.
While the new HD trucks stand two inches taller than the Silverado/Sierra 1500s, it is not due to a different or modified suspension. Rather, the cab and bed have been raised with taller body mounts. Interestingly, GM will use the same torsion-bar independent suspension for both 2WD and 4WD trucks. The new 4WD front differential, we were told, will be larger than the unit used in current 1-ton models.
As one might expect, the rear suspension remains solid-axle leaf-sprung. However, there will be a larger optional axle to complement the venerable 10.5-inch ring gear corporate 14-bolt. This axle has a massive 11.5-inch ring gear.
The new NVG261 transfer case is expected to have the same push-button 2WD, Auto 4WD, 4WD Hi, Neutral, and 4WD Lo functions as the Autotrac NVG246 transfer cases in light-duty models. We were told lever actuation would be an option.
Since GM elected not to create a completely separate HD truck line (as Ford did with the Super Duty), it's no surprise that the 2500HD and 3500 look similar to their light-duty brethren. Careful observers will note that the front end styling is unique and just a shade more aggressive than light-duty models. The complete listing of chassis configurations and wheelbases were unavailable at press time, but we expect there to be more options available than the current mix, and they may include an extended-cab shortbox. All 3500-series trucks will be equipped with dual rear wheels.