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…