- TRUCKIN.COM [1 9 ] NOVEMBER 2019 -
DURAMAX I-6 GOODNESS
General Motors is rightly proud of the engine’s torque curve,
which boasts a peak 460 lb-ft between 1,50 0 and 3,0 00 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 tempera-
tures, 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 of-
fers 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 leads to reduced friction, improved ef-
ficiency, and better noise/vibration/harshness isolation.
CONSTRUCTION ZONE
One question on our minds is how durable the Duramax I-
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 V-shaped
engines, offering lots of strength and lighter construction than tra-
ditional 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 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 ac-
curately 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) oper-
ate each of the engine’s 24 valves, which feature maintenance-free fin-
ger 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 im-
prove combustion. Paired with a high-pressure EGR, the low-pres-
sure 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 in-
creasing emissions.
A variable intake manifold provides two paths into each cylin-
der—a short and a long one. Electronic flaps select which air path
to use, improving engine response, particularly at low rpm. Mean-
while 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 0W 20 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 distrib-
utes 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 par-
asitic 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 negative 22 degrees Fahrenheit.
Finally, common-rail direct injection—a feature General Motors
pioneered with the 6.6L Duramax LB7 V-8 found in the ’01 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 pro-
vide 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 GM is playing to win
against the Ram 1500 EcoDiesel and the Ford F-150 Power Stroke.GM hasn’t announced official numbers yet, but expect the 3.0L Duramax to be
the fuel economy champ of the Silverado/Sierra lineup, and if it doesn’t boast
class-leading towing figures, at the very least the diesel engine and 10-speed
transmission should be very competent when lugging heavy trailers.The Chevrolet Silverado and GMC Sierra join their domestic competition in
offering a light-duty diesel. While the Ram EcoDiesel and the Ford 3.0L Power
Stroke are V-6s, the middle-child Duramax is a straight-six, offering improved
torque and smoothness.