General Motors has revealed the key specifications for its new 8.3-liter Duramax diesel, and the engine now leads the heavy-duty pickup truck class in both horsepower and torque. The new “Mongoose” produces 555 horsepower and 1,230 pound-feet of torque, while GM has also upgraded the Chevrolet Silverado HD and GMC Sierra HD with improved brakes, steering, and a more powerful gas V8.
GM’s New Duramax Beats Ford’s PowerStroke
Ford has held the factory diesel performance benchmark in recent years with its high-output PowerStroke V8, nicknamed “Scorpion,” which produces 500 horsepower and 1,200 pound-feet of torque.
GM has now surpassed those figures with its new 8.3-liter Duramax, named “Mongoose.” The engine delivers 555 hp and 1,230 lb-ft of torque. The horsepower increase over Ford is more substantial than the torque gain, but the improvement over GM’s previous Duramax is considerably larger.
The outgoing Duramax produced 470 hp and 975 lb-ft of torque, giving the new engine increases of 85 horsepower and 255 pound-feet of torque.
GM did more than simply increase displacement to reach those numbers. The new diesel uses a compacted-graphite iron block and fully forged steel internals, including the crankshaft, connecting rods, and pistons.
Engine cooling has also been improved, while a variable-geometry turbocharger sends boost through a new dual-stage air-to-water intercooler. Power continues to be delivered through GM’s 10-speed Allison automatic transmission.
New Silverado HD and Sierra HD Towing Capacity
The new diesel also increases the towing capability of the Chevrolet Silverado HD and GMC Sierra HD. With the right configuration and a fifth-wheel setup, maximum towing capacity now reaches 38,000 pounds.
That figure surpasses the Ram 3500 and matches the Ford F-350 Super Duty. Ford’s F-450 Super Duty remains ahead with more than 40,000 pounds of fifth-wheel towing capacity.
For conventional towing, the new GM trucks are rated for up to 20,000 pounds. Ford remains ahead in this category, offering up to 28,000 pounds with a normal bumper-mounted hitch.
Why GM Chose Compacted-Graphite Iron
Compacted graphite iron, or CGI, has been used in the automotive industry for decades. It was patented in the 1940s and became more popular during the 1980s.
CGI’s first commercial application is generally considered to have been high-speed train brakes in parts of Europe. Traditional cast-iron brakes were cracking and warping under the heat produced when stopping trains traveling at more than 175 miles per hour.
The material later became more widely used in the automotive industry, particularly in diesel engines. Its advantages include better thermal conduction than regular cast iron, improved vibration and sound damping, greater stiffness, low thermal expansion, and machining characteristics similar to other common types of iron.
CGI can withstand heat and pressure better than ductile or gray iron, making it a durable and robust material for GM’s new diesel. The block can handle more than 200 bar of cylinder pressure, or 75% more pressure than gray iron. It also dissipates heat more quickly and is quieter than aluminum blocks.
GM Upgrades the 6.6-Liter Gas V8
GM also upgraded its existing 6.6-liter gas V8 for buyers who are not interested in a diesel. The changes include a revised intake manifold and oil cooler setup, along with improvements to the lubrication system.
Those updates raise output from 401 to 412 horsepower and increase torque from 464 to 472 pound-feet. GM’s gas V8 now produces more torque than the engines offered by Ram and Ford, although Ford still leads in horsepower despite having an additional 0.7 liters of displacement.
Silverado HD and Sierra HD Get New Brakes and Steering
GM has also upgraded the braking and steering systems on its heavy-duty pickups. The front brake discs now measure 14.6 inches in diameter and use fixed four-piston calipers.
The trucks also switch to an electronic brake booster. For steering, GM has eliminated hydraulic assist in favor of an electric-assist system.
GM says the new steering system reduces complexity and part count. Combined with rack-and-pinion steering, the setup is intended to provide greater accuracy and precision than the recirculating-ball designs used by Ford and Ram.
New Terrain Mode for ZR2 and AT4X Trucks
GM has also added a new drive mode to the ZR2 and AT4X off-road versions of its heavy-duty trucks. Terrain Mode joins the existing Off-Road Mode.
The new mode enables one-pedal driving while off-road in both low- and high-four-wheel-drive settings, adding another upgrade to GM’s heavy-duty truck lineup.
