Deep Dive: 2020 General Motors 3.0L Duramax I-6
High-Tech Diesel Boasts Some Common Wisdom
General Motors will soon begin to market a 3.0L Duramax I-6 turbodiesel in its light-duty pickup offerings, the Chevrolet Silverado 1500 and the GMC Sierra 1500. And although we were a bit disappointed to learn the engine would be delayed until the 2020 model year, for fans of oil-burning powertrains, it might be worth the wait.
Helping ease the sting of the delay is the relative low cost of the Duramax I-6. In the 2020 Silverado 1500, the diesel will demand the same premium as the 6.2L V-8, $2,495 more than the 5.3L V-8 and $3,890 more than the 2.7L turbocharged I-4. For 2020, the Duramax will be offered in LT, RST, LTZ, and High Country trims. Using 2019 prices as an estimate, one could potentially get a two-wheel-drive, diesel-powered Silverado RST for about $47,000 or a four-wheel drive for $50,00—the caveat being that exact pricing for 2020 has yet to be revealed.
Duramax I-6 Goodness
General Motors is rightly proud of the engine's torque curve, which boasts a peak 460 lb-ft between 1,500 and 3,000 rpm, with more than 430 lb-ft available at 1,250 rpm—as well as 277 hp at 3,750 rpm. A variable-geometry turbocharger helps enable lag-free torque delivery, at least theoretically, with a maximum of 43.5 psi of boost. A water-to-air intercooler helps reduce charge-air temperatures, improving both performance and engine durability.
And while Ford and Ram both use a DOHC 3.0L V-6 for their light-duty diesel pickups, GM says the Duramax I-6 is a better choice for a truck thanks to the inline engine's inherent smoothness. An I-6 offers balanced primary and secondary rotational forces, precluding the need for a balance shaft. No balance shaft and the DOHC I-6's need for only two camshafts lead to reduced friction, improved efficiency, and better noise/vibration/harshness isolation.
One question on our minds is how durable the Duramax I-6 will be since the engine block is made from cast aluminum—both Ford and Ram make use of tough compacted graphite iron (CGI) for their engine blocks. CGI is an effective material for vee-shaped engines, offering lots of strength and lighter construction than traditional iron. To its credit, GM makes use of iron cylinder liners to help the engine block hold up under the compression and ignition forces a diesel engine undergoes. And aluminum offers a 25 percent weight savings over a comparable iron-block construction.
The Duramax I-6 engine's deep-skirt design (where the block casting extends below the crankshaft's centerline) helps add strength, as do seven nodular iron main bearing caps that help accurately locate the forged steel crankshaft and connecting rods. Hypereutectic pistons feature blended silicon and aluminum for high heat resistance and improved tolerance. A thick piston crown and reinforced piston ring help it withstand the high turbocharger pressures and the engine's own compression ratio of 15.0:1.
A single set of dual overhead camshafts (it's an I-6, remember) operate each of the engine's 24 valves, which feature maintenance-free finger followers and hydraulic lash adjusters. Owing to the engine's length, the camshaft drivetrain is on the back of the engine. A chaindrive on the crankshaft operates the high-pressure direct-injection fuel pump, and a chain on the fuel pump runs to the intake and exhaust cams. A smaller belt on the crankshaft runs the variable-flow oil pump.
Auxiliaries and New Tech
There's a new low-pressure EGR system on the Duramax I-6, and like other EGRs, it helps reduce intake temperatures and improve combustion. Paired with a high-pressure EGR, the low-pressure system helps reduce parasitic boost losses, and an electronic valve system helps the engine prioritize high- or low-pressure EGRs to improve turbocharger operating efficiency without increasing emissions.
A variable intake manifold provides two paths into each cylinder—a short and a long one. Electronic flaps select which air path to use, improving engine response particularly at low rpm. Meanwhile a variable-pressure oil system uses a continuously variable-displacement oil pump, optimizing oil pressure relative to engine speed and power demands. Low-friction Dexos 0W20 diesel oil improves efficiency further.
Oil jets located in the block target the inner core of the piston for an extra layer of protection, reducing temperatures within the block and improving power production and durability goals.
A turbodiesel engine operates most effectively in a relatively narrow temperature window. As such, the 3.0L Duramax I-6 features Active Thermal Management, a feature also seen on GM's high-tech 2.7L turbocharged I-4. A three-actuator rotary valve system distributes coolant to specific targets, cooling more temperature-sensitive parts of the engine while leaving other bits less targeted.
This helps maintain thermal efficiency while also reducing parasitic losses caused by cooling parts of the engine that don't need cooling. Ceramic glow plugs heat up faster and more evenly than conventional glow plugs, helping the engine start faster and heat up more quickly. A related side effect is that the engine can start on its own at temperatures as cold as minus 22 degrees F.
Finally, common-rail direct injection—a feature General Motors pioneered with the 6.6L Duramax LB7 V-8 found in the 2001 Silverado and Sierra HD—appears on the smaller D-max. Featuring a staggering 36,250 psi of injection pressure, the system sends fuel via an engine-driven pump to solenoid-activated injectors, each with a nine-hole nozzle to optimize fuel atomization and deliver precise metering. Capable of multiple injections per cycle, the system also helps provide more complete fuel combustion for reduced emissions.
Compression Ignition Anticipation
The 3.0L Duramax I-6 is General Motors' first turbodiesel straight-six to appear under the hood of one of its pickups, and by the looks of it, the company threw as much of its engineering prowess at the powerplant as it could. Aside from minute suspicions about its all-aluminum engine construction, it looks like it will be a standout in the light-duty industry. While we're still waiting on official towing, payload, and fuel efficiency numbers, it's clear that GM is playing to win against the Ram 1500 EcoDiesel and the Ford F-150 Power Stroke.
Source: General Motors