Heavy Duty Heaven

October 4, 2010 09:54 AM
 

 IGP1575

Massive improvements in frame, suspension, payload and towing ability put the 2011 Chevy and GMC heavy-duty trucks at the top of their segment. Power and fuel mileage have also improved, and the new suspension keeps the power under control and the tires planted on the pavement.
I tested the mettle of these new models by hooking a Sierra 3500 Dura-max diesel dually (397 hp/765 lb.-ft. of torque) to a 12,800-lb. horse trailer. The Allison tranny grade shifted in step with the new exhaust brake, keeping my foot idle. The exhaust brake closes the vanes on the turbine side of the turbo to create back pressure and has four operational modes. You can toggle down gears by switching from auto to manual with the cruise control on.


The truck held fourth gear well, under 3,000 rpm on a 9% grade. The 172° tranny temp showed how little the transmission was doing. In tow haul mode, downshifts are easy to hold for more braking and hold range longer.


The latest Duramax LML features a high-pressure (30,000 psi) Piezo-actuated fuel system for 11% greater fuel efficiency, improved performance and reduced emissions. Exhaust gas recirculation is dual-cooled with a hot bypass. New injectors, pump and a unique downstream injector past the turbo for regeneration keeps the heat out of the engine, which is a benefit with B20 biodiesel compatibility.

High-end heavies. The Denali is for farm managers and owners who spend days in the truck. The big changes are under the skin. The new steering box, ratios and linkage add up to tighter steering. The hydraulic body mounts under the cab improve the ride.


I towed a 10,500-lb. skid steer trailer with the comfy 2500 Denali’s 6.0-liter engine (360 hp/380 lb.-ft. of torque) and 3.73 axle ratio. The gas V-8 held 5,000 rpm in tow mode, then shifted at 5,600 rpm, dropping to 3,500 rpm for the next gear, which is a good range for staying in the power band.


The 14" brake rotors are almost the same size front and back—more than a 1" increase from last year. The proportional brakes can change pressure front to back where the most brakes are needed.


SRW trucks have a new trailer sway control with integrated trailer brake control. With hill start assist, the truck and trailer brakes hold for a couple of seconds while you go from brake pedal to gas pedal.


The new asymmetrical design of the rear suspension minimizes axle hop and enhances traction control. The 2500HD models feature a two-stage leaf-spring design; 3500HD models have a three-stage design. All feature 3" leaf springs, 20% wider than previous models.


The frame is all boxed, so beam stiffness is increased by 20%, frame bending strength by 92% and torsional rigidity fivefold. Ladder frame cross members are welded instead of riveted, with an extra above the spare tire.


The independent front suspension has forged-steel upper control arms, cast-iron lower arms with bigger shock towers and a pair of urethane jounce bumpers on each side. Larger wheel hub and bearing assemblies complement the new brake system.


The new emissions diesel uses diesel exhaust fluid, which basically costs what it saves in improved miles per gallon. The tank is outside the frame under the passenger side. It holds close to 5 gal., with a range of 5,000 to 8,000 miles, and fills under the hood.


Combustion and after-treatment provide about 700 miles between diesel particulate filter regenerations, a 75% improvement over the previous system and a significant contributor to improved fuel efficiency.

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