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GM’s New I-6 Diesel

Half-ton Silverados, Sierra get a new six-cylinder diesel, V-8 gas engines, and 10-speed tranny.

General Motors’ innovations on its GMC and Chevy half-ton line have been mostly focused on enhanced creature comforts the last couple of years.

But in 2020, power and putting it to work gets all the attention.

For starters, GM engineers created an entirely new six-cylinder Duramax diesel for Silverado and GMC Sierra 1500 vehicles. This 3.0-liter powerplant employs six (inline) turbocharged cylinders that turn out 277 hp. and 460 foot-pounds of torque. 

This innovation represents the first-ever six inline turbo diesel offered in GM full-size light-duty trucks. GM revealed that the I-6 diesel will be priced identically to the 6.2-liter V-8, as a $2,495 premium over its 5.3-liter V-8 model, or $3,890 over the 2.7-liter turbocharged four-cylinder engine.

“From the moment the engine is started, to its idle, acceleration, and highway cruising, the (I-6) Duramax performance will change perceptions of what a diesel engine can offer in refinement,” says Nicola Menarini of General Motors.

I-6 Diesel Features

Innovations abound in the new six-cylinder Duramax including the following.

  • An engine cylinder block fashioned from cast aluminum alloy provides the strength required to support the higher combustion pressures within a diesel. Through the use of aluminum, that engine provides a weight savings of approximately 25%.
  • Seven nodular iron main bearing caps ensure block strength while also enabling accurate location of the rotating assembly.
  • A deep-skirt block design, where the block casting extends below the crankshaft centerline, contributes to the engine’s stiffness.
  • A thick piston crown and reinforced top ring add strength to the piston that supports the higher cylinder pressures created by turbocharging and the engines’s 15-to-1 compression ratio.
  • A variable-geometry turbocharger uses closed-loop controlled vanes and electronic controls that automatically adjust boost pressure to the desired value based on engine running conditions.
  • Has a new low-pressure exhaust gas recirculation design.
  • A variable intake manifold offers dual air intake pathways for each cylinder.
  • A variable-pressure oiling system with a continuously variable-displacement vane pump optimizes oil pressure as a function of engine speed and load.

The existing 6.6-liter turbo Duramax V-8 diesel remains available in 2020 offering 445 hp. and 910 foot-pounds of torque.

New 10-Speed Tranny

For good measure, GM half tons will also get an all-new 6.6-liter V-8 gas engine (the standard equipment engine) that turns out an impressive 401 hp. and 464 foot-pounds of torque. That engine is mated to GM’s existing six-speed Allison automatic.

GM diesels, however, will be mated to a brand-new 10-speed Allison automatic. That transmission was designed with additional gears (the previous Allison tranny was a six-speed affair) that allow more torque to be put to the ground in lower gear ranges, providing for smoother gear changes and shorter steps between them when trailering. The new Allison supports smart engine braking.

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