What’s 220 pounds to General Motors’ new 6.6-liter Duramax diesel V-8 engine? Not much, based on the minuscule differences between the performances of the 2017 GMC Sierra 2500HD tested here and a slightly smaller, extended-cab Chevrolet Silverado 2500HD with the same engine we tested earlier this year. This 8000-pound GMC—a high-zoot, crew-cab Denali model—is 9.5 inches longer and 220 pounds heavier than that Silverado, yet it trails the Chevy to 60 mph by only 0.3 second and by 0.2 second through the quarter-mile. This “slower” four-ton truck’s performance figures are remarkable: 6.5 seconds to 60 mph and a quarter-mile time of 15 flat at 91 mph.
Rather than list the lighter-weight, more performance-oriented passenger cars that can match that feat, we’ll just say that piloting so much vehicle so quickly is a unique thrill. Imagine going neck and neck with a Fiat 124 Spider off the line while driving your house. It’s a bit like that. All credit goes to the updated Duramax diesel engine, which added $8800 to the bottom line of our Sierra 2500HD test truck. Shared with the Silverado, the V-8 puts out 445 horsepower and 910 lb-ft of torque. It’s the headline upgrade to the 2017-model Sierra 2500 and 3500 trucks, which otherwise change only with the additions of a ram-air hood scoop for Duramax-equipped models and a newly available, dealer-installed lane-change camera system.
About that Engine . . .
The Sierra’s 6.6-liter Duramax diesel shares only its iron block and valvetrain layout with its predecessor. Everything else is new, including the turbocharger, aluminum cylinder heads, control unit, crankshaft, pistons, and exhaust. The result is a 48-hp jump over last year’s Duramax, while torque swells by a whopping 145 lb-ft. Although GM says the new engine is quieter than before, thanks to refinements and an insulated oil pan, the clattery rat-tat-tat diesel soundtrack is still (faintly) audible inside the cabin—even if the 67 decibels we measured inside at 70 mph are luxury car–like.
Less luxurious are the environs in which all of these toys are installed. The GMC is getting old, and the plain-Jane, rectilinear interior betrays its age in spite of the fancy veneer added by the Denali trim. Other rigs’ top-flight models do more convincing luxury-car impressions, particularly Ford’s Platinum spec. The F-series also has the Sierra beat with modern active-safety tech such as adaptive cruise control and lane-keeping assist. The GMC has only lane-departure warning, forward-collision warning, and the previously mentioned new dealer-installed trailer camera system that beams a feed from the attendant side mirror to the central display when a turn signal is activated. This feature wasn’t included on our test truck, but we’ve tried it on the Silverado and found it useful, if redundant—properly adjusted blind-spot mirrors show basically the same view and don’t require the driver to study the dashboard display while in motion.
The argument could be made that the old-school steel Sierra 2500 doesn’t need newfangled technology to bolster its appeal. Pricey Denali trim aside, the GMC is a straightforward tool, one with an incredible diesel engine option.