First Look: The Tech Details Behind the 2020 Silverado’s New 3.0L Duramax I-6 Turbodiesel

Right Inline

The last time Chevrolet offered a straight-six engine was in the '08 Trailblazer. That fuel-injected 4.2L gas-burner made 273 hp and 277 lb-ft of torque, with a combined EPA fuel economy rating of 16 mpg on the 4WD model. The inline-six was impressive, winning numerous awards for its innovations. But it's nowhere near as impressive as the inline-six Duramax diesel that makes its debut in the '20 Chevrolet Silverado.

GM's newest diesel, the third offering in the Duramax family, is 3.0 liters of high-tech innovation wrapped in an aluminum block and head. It delivers 277 ponies and 460 lb-ft of torque, coupled with fuel economy numbers expected to be in the 30s. The 3.0L Duramax has more horsepower than its Ford Power Stroke and Ram EcoDiesel rivals, and it flexes its torque muscle lower in the rpm band than both competitors.

From what we experienced in our first drive of a Silverado with this engine, the inline-six Duramax, which makes more torque than the Silverado's available 6.2L V-8 and is backed by the same 10-speed automatic as found in the Camaro ZL1, is a sweet package for those who want a nice balance of towing muscle and fuel economy in a 1/2-ton pickup. It's quick, smooth, and quiet.

Clean-Sheet Design
Other than the name, the 3.0L inline-six has little in common between the 2.8L I-4 Duramax found in the Colorado/Canyon and the 6.6L V-8 Duramax under the hood of the 2500/3500 HDs.

"It is a clean-sheet design from the air intake down to the engine mounts," said John Barta, assistant chief engineer for the new Duramax. "Very, very few common things were used from the other Duramaxs. We've optimized everything in this engine's design to fit into the new-generation Silverados while incorporating advanced combustion and emissions technologies to optimize performance and efficiency."

GM opted for the cast-aluminum inline-six design because the architecture keeps it light and makes it easier to find the right balance between fuel economy and power. The dual-overhead-cam inline-six has many advantages for us, especially when it comes to efficiency.

"Because the layout of the inline-six is naturally balanced, we don't have to have any balance shafts," explained Barta, as he took us on a walkaround of the new diesel. "That helps reduce friction inside the engine and improves the overall efficiency."

Tough Guts
GM says the 3.0L Duramax cylinder block, which uses iron cylinder liners, is approximately 25 percent lighter than a comparable cast-iron engine block weighing in at a svelte 467 pounds—the same as the optional 6.2L LS3 V-8.

It's also stout on build quality. The forged-steel crankshaft sports seven nodular-iron main bearing caps, a deep-skirt block design, and an aluminum lower crankcase extension attached to the main bearing caps where the block casting extends below the crankshaft centerline, all of which contribute to the engine's stiffness and refinement.

Silicone is blended with the aluminum for heat resistance and tolerance within the piston cylinders, which enhances performance and helps make the engine quiet. They also have a thick crown and reinforced top ring, which add strength to support the tremendous cylinder pressures enabled by turbocharging and the engine's modest (for diesels) 15.0:1 compression ratio.

The dual camshafts are chaindriven from the rear to keep the packaging as compact as possible for the inline-six, which is several inches longer than the V-8s. The crankshaft also runs the high-pressure, direct-injection fuel pump and the smaller variable-flow oil pump via an oil-submerged drivebelt.

New EGR/SCR
Apart from the dual cams and rear chaindrive system, one of the first things we noticed about the 3.0L Duramax was how the exhaust from the turbo immediately feeds into the emissions scrubbing components and is smoothly integrated on the passenger side of the block beneath the turbo. There's no DPF (Diesel Particulate Filter) on the exhaust under the truck.

Unlike its big brother, the 3.0L Duramax doesn't have a traditional DPF. The clean-sheet design allowed the engineers to combine the SCR (Selective Catalytic Reduction) and DPF into one unit, which Barta's group refers to as the "SCRF."

"The SCRF is coupled close enough to the turbo that we actually do the regen post- injections on the exhaust stroke, and that extra fuel flows out the exhaust valve and straight into the SCRF," said Barta. This design makes the "passive regens" automatic and seamlessly unobtrusive to the driver.

The 3.0L Duramax also incorporates a dual-circuit EGR (Exhaust Gas Recirculation) system. The low-pressure and high-pressure circuits are controlled by an electronically controlled exhaust throttle valve located where the exhaust flowing under the truck connects to the SCRF outlet.

This design opened the door to continual adjustment of exhaust backpressure for more efficient operation by recirculating exhaust gases between the low-pressure points in the exhaust system and after the compressor inlet.

When the new coolant-cooled, low-pressure EGR is activated by an electronically controlled valve, the engine burns exhaust gas that has already passed through the SCRF. That increases the turbocharger's efficiency, which helps overall vehicle efficiency without deteriorating the rate of particulate matter emitted by the engine.

Barta told us the SCRF allowed engineers to combine the DOC (Diesel Oxidation Catalysts) and SCR components into one unit alongside the engine so each element heats up quickly for excellent emissions control.

Breathing Power
Diesels thrive on a good supply of cool air and perfectly delivered fuel. The 3.0L Duramax delivers both. It relies on Denso common-rail fuel-injection components just as the newest 6.6Ls do. The difference between the 6.6L Duramax and the 3.0L is the inline-six injection system pushes diesel to the nine-hole injectors at up to 36,250 psi with the engine computer managing up to 10 injections per cylinder event.

That fuel delivery management, coupled with a Honeywell VGT (Variable Geometry Turbocharging) turbo and a variable dual-intake for each cylinder, makes for one quick-responding diesel with a wide powerband and excellent fuel efficiency.

The charge-air-cooler (CAC) is located on top of the inline-six's valve cover instead of in the radiator stack behind the grille. "We feed the turbo with cooled air through our water-cooled CAC," said Barta, pointing to the top of the engine. "It's very efficient packaged in this manner. We can drop the temperatures up to 100 degrees into the end of the turbo depending on the conditions."

The clean-sheet design resulted in an intake with a very short column of cool, high-density air feeding the VGT turbo. At full boost of 29 pounds, the Duramax inline-six makes 460 lb-ft of torque at 1,500 rpm, with an impressive 95 percent of that pulling power coming in at 1,250 rpm, according to Nicola Menarini, director for Diesel Truck Engine Program Execution.

"From the moment the engine is started, to its idle, acceleration and highway cruising, the 3.0L Duramax performance will change perceptions of what a diesel engine can offer in refinement," said Menarini.

First-Drive Impressions
Our first drive of the 2020 Silverado 1500 Duramax revealed this engine is ideally suited for the Silverado 1/2-ton. It pulls strong from down around 1,200 rpm all the way up to 4,500 rpm, with no apparent signs of turbo lag. It's also whisper quiet inside and out. In fact, the only noise we could hear rolling down the interstate at a leisurely 65 mph was the subtle whisper of wind rushing past the truck's mirrors.

The engine starts instantly and idles so smoothly that one almost forgets it's running. GM has coupled the new Duramax to the same 10L80 10-speed automatic transmission as found in the '18-newer fullsize GM SUVs as well as the Camaro SS/ZL1, and, as odd as it may sound, in the Ford Mustang GT. (The transmission was developed as a joint venture with Ford Motor Company. Ford calls its version the 10R80.)

We'll skip all the chat about the truck itself because we covered all of that during our 2019 Pickup Truck of the Year coverage a few months ago. What we can say is the midsize Duramax makes its V-8 big brother proud.

The heavy-duty 10-speed automatic has all the right gear splits needed to give the 1/2-ton diesel the optimum gearing for the moment at hand—even with the 3.23:1 axle ratio. You can hammer the throttle off the line and all the computers get their handshakes done quickly, and then the turbo rapidly spools up, setting you back in the seat with a firm push as the 10L80's low 4.70:1 First gear goes to work.

Need to pass? Easy peasy. There's no hesitation making a pass at 55 mph. The 10L80 downshifts smoothly, bringing the engine up to 3,500 rpm at the same instant the turbo spools up to give the same near-instant acceleration as one finds with the 5.3L V-8. The cool part is that under hard throttle like this, the inline-six Duramax pulls strong to 4,000 rpm, and then the 10L80 makes a smooth, near-instant upshift, dropping the rpm to 3,500; the scenario repeats as long as you keep the hammer down—or the speed limiter kicks in just past the magical century mark. It's an impressive engine/transmission combination.

Under normal driving conditions the engine and shifts are nearly seamless. Hills and mountain grades require almost no change in throttle to maintain whatever speed you need or have cruise control locked into.

EPA mpg numbers for the 3.0L Duramax are 23 city and 29 highway in 4x4 configuration. The indicated mpg on our 4x4 Silverado's DIC hovered around 35 mpg while cruising along at the posted 55 mph speed limit on the relatively flat highways just outside of the Brasada Ranch resort area a few miles north of Bend in Central Oregon. That observed mpg number dropped only slightly (31-33) when we hit I-97 and rolled up to 65 mph, thanks in no small part to the diesel's fuel-management algorithms and the 10L80's triple overdrives.

We were not afforded the opportunity to slide a trailer on the hitch during our brief time with the '20 Chevrolet Silverado. But from our seat time we have little doubt the max tow rating of 9,300 pounds (properly equipped) show the Duramax-powered Silverado will be every bit as capable as its V-8 counterparts when it comes to pulling a boat, a horse, equipment, and travel trailers.

We can't wait to put a Duramax-powered Silverado 1/2-ton to the full test, on-road and off, to see how it performs.

The Duramax package is priced identically to the 6.2L V-8 as a $2,495 premium over a 5.3L V-8 model, or $3,890 over a 2.7L turbo model. It's offered on LT, RST, LTZ and High Country models, giving Silverado buyers six propulsion choices, each tailored to suit customers' needs for performance, efficiency, technology and value.

Engine Specifications
Type: Duramax 3.0L I-6 DOHC turbodiesel
Bore & stroke (in): 3.30 x 3.54 inches
Block material: Aluminum
Cylinder head material: Aluminum
Compression ratio (:1): 15.0
Firing order: 1-5-3-6-2-4
Valvetrain: Dual-overhead camshafts, four-valves per cylinder
Air delivery: Single variable-geometry turbocharger; intercooling system. 42.8-psi/2.95 bar max boost
Fuel delivery: High-pressure, common-rail direct injection (36,250 psi); electronic throttle valve
Ignition system: Compression
Max engine speed (rpm): 5,100
Additional features: Continuously variable oil pump; engine oil cooler, automatic stop/start, Active Thermal Management
Emissions control: Low-pressure Exhaust Gas Recirculation (EGR); Selective Catalyst Reduction on Filter (SCRF)
Horsepower @ rpm: 277 @ 3,750 (SAE certified)
Torque (lb-ft @ rpm): 460 @ 1,500 (SAE certified)
Manufacturing location (of globally sourced parts): Flint, Michigan

1/2-Ton Pickup Diesel Engine Comparison

Chevrolet Duramax Ford
Power Stroke
Ram EcoDiesel
Displacement 3.0L 3.0L 3.0L
Configuration I-6 V-6 V-6
Torque ) lb-ft @ rpm 460 @ 1,500 440 @ 1,750 480 @ 1,600
Horsepower (@rpm) 277 @ 3.750 250 @ 3,250 260 hp @ 3,600
Weight (lb) 467 501 550
Block Aluminum Iron Iron
Head(s) Aluminum Aluminum Aluminum
Compression 15.0 16.0 16.5