First Look: GM’s 2.8L Duramax

Canyon/Colorado and Beyond?

To say that diesel is becoming mainstream in America is still a stretch; the reality is that more and more companies are coming forward with sophisticated diesel powerplants that will eventually end up in some cool vehicles. New diesels will help manufacturers meet more stringent CAFÉ (Corporate Average Fuel Economy) standards that the government is demanding. The good news is that rather than doing it with hybrids and battery packs, manufacturers are using an existing infrastructure combined with new technology to make power and mpg. A prime example is the all-new 2.8L Duramax unveiled at the Detroit Auto Show.

At the show, General Motors introduced a new small diesel for North America, an engine designed purely for trucks. Diesel World got an exclusive in-depth interview with Scott Yackley, Assistant Chief Engineer for the global project.

The engine, though new to the North American market, has been on sale globally since 2011. It launched with 2.5- and 2.8-liter versions of the motor we will have starting in model year 2016. This revised 2.8-liter motor has significant changes that will be rolled out globally with some changes specific to our North American market.
Yackley told DW that at its core, the block, crank, cylinder head, all the valve train, the camshaft and the entire top end are common with the global application. “The reason we’ve done that is it’s a proven engine around the world in key markets… (from) 2011 when we launched it.” Thus, GM is confident that the engine is well shaken down, well proven and “nothing new when it comes into the market” here in the U.S. Well, that’s not the whole story; it’s not even close.

For one, GM named it Duramax, one of the premier engine families, which means there’s trust in the updated motor. Yackley said, “(The 2.8-liter) follows the same validation and testing as the bigger Duramax engines. Also, this is a truck-specific engine. It’s for trucks, not designed for a car.” That’s not just empty words or bragging, as you’ll see from the cutaway engine photos.

We began to chat about the nitty-gritty details, the features that diesel enthusiasts want to know about. According to the lead engineer, who shepherded development from Italy to Germany to Pontiac, Michigan, the motor uses a forged steel crank machined in-house at GM’s plant in Rayong, Thailand. That facility has all the latest technology for machining and balancing crankshafts and other parts, and it’s all done in a clean room atmosphere. The crank itself is fully balanced. Yackley says the raw forgings are received from a supplier and then machined in the Thailand facility. “It’s the same with the cast-iron block,” Yackley added. “We do head, block, crankshaft, camshaft machining and assembly in Thailand.”

The head is cast aluminum with newly enlarged exhaust ports, bigger water passages, and an improved oil distribution channel for in-head lubrication. Pistons are nothing exotic. Instead, a proven traditional deep-dish design with a typical three-ring design—a top, middle and oil ring—is used. Notably, pistons are specific. “We recently, for 2014, made a global upgrade co-designed for the North American market and it includes new pistons specific to meeting emissions in North America.” Yackley explained. Piston-cooling oil jets are part of the package. In addition, there’s a new fuel system for 2014, which will flow into the market when the engine begins to ship sometime next year.

We asked about the valve train. Not surprisingly, the aluminum head contains dual overhead cams with a roller finger follower actuator system. The camshafts are tubular, utilizing cast steel sintered lobes that are pressed onto the camshaft, and then machined. Valve springs are standard and the seats are sintered metal pressed in, then later machined.

For the fuel system, which is solenoid operated at 2,000 bar or 29,000 psi, the suppler is DENSO. High pressures like this improve engine efficiency for better performance and at the same time reduce CO2 and fuel consumption. That’s a big win. DENSO provides the total system, injectors, supply pump and fuel rail. While we’re on the fuel system, GM has switched ECU or engine control units from Bosch control systems to Continental. Bosch remains the supplier for the 2.0-liter diesel. Like that smaller motor, all the software controlling the engine is created in-house, then supplied to the controller maker to burn onto the silicon. This will be the first GM engine with Continental diesel engine controllers in the U.S., we’re told.

For the necessary turbocharger, a Honeywell variable-geometry turbo was selected, and it’s water-cooled. Yackley said that the output pressures “are still being optimized,” so we figure boost will be somewhere in the mid 20-psi range. According to the same source, “The turbo casting is the same as the global variant, but we’ve retuned it (for the USA) with a new compressor wheel.” He explained that the retooling was done to optimize high-altitude capability. “That’s one thing we don’t have to worry about in global markets, but in the U.S., we have higher altitudes, and we have to meet emissions standards at high altitude.” We suggested this opens new business opportunities in Tibet.

Though sold in Asia, Australia and South America, none of those markets have the harsh winters, Death Valley summers, nor the stringency of emissions regulations we have here.

All modern diesels require NOx abatement in the U.S. This engine employs up to 40% EGR to avoid excess oxygen in the cylinders, which could increase NOx. Note that all engines now have the oil pump driven off the balance shaft, gear-to-gear drive. In front, the crank drives the vacuum pump, again driven gear-to-gear and the engine uses a soft timing belt that’s good for a 150,000-mile service interval. It was selected for packaging, lower noise production, and serviceability to -40° F.

Yackley explained a series of North America-specific enhancements and refinements were needed for American customers, especially in the noise, vibration, and harshness (NVH) arena. “The targets we set for the engine and as it’s integrated into the vehicle are high.” He says the trucks have a premium level acoustic package; acoustic damping in the front of the dash, surrounding the engine cover, and we’ll bet on a bit of extra at the firewall, particularly for the GMC Canyon. The display engine does not have all of its acoustic package installed, better to show the engine. Production engines will have a layered and stacked system with sound absorbent around the injectors and rail, the valve train, and a composite cover over the top. In addition, a composite intake manifold and dampened belt cover contribute to lower noise.

So we asked if all that was necessary with the quietness delivered by modern multi-injection strategies? Yackley replied, “We’re going to have a multi-injection strategy, pre and post, even multiple-post injections, a broad response we’re still dialing in, but very broad for emissions and performance. Also to smooth it out for various operating cycles. In addition to the acoustic covers, we did put a damped steel timing belt cover on the engine, and a damped steel lower addition to the oil pan (photo). It’s attached directly beneath the balance shaft. So we’ve got treatments at the top, the front, and the bottom of the engine to reduce noise as much as possible.”

Yackley also offered that diesel-equipped Canyon and Colorado trucks will be the first in segment with hydraulic motor mounts and they will be standard with the engine. The engineer says that, in combination with a balance shaft, inherent inline four-cylinder engine shaking forces will be reduced. The engine has a new balance shaft housing that’s more centered in the engine. Why? “When you grab the steering wheel, often on four cylinders you get a lot of shaking,” Yackley answered. “You won’t here.”

For the engine team, NVH was one of the key areas of necessary work: combustion noise, injector noise, valve train noise, timing system noise. They were set on trying to deaden as much noise as economically possible. “Sometimes you’re sitting at idle—that’s another thing, not just improving in-cabin but outside the vehicle—from 25 feet away the package is really good. Even in the cabin you’re wondering ‘is this the V-6 with direct injection or a diesel?’ All of which requires attention to detail.”

Noise was one target for GM, temperature tolerance another, especially cold temperatures. Currently, Colorado’s global market is mainly South America, Asia and Australia, not Europe or Russia. So inherently the first 2.8-liter didn’t focus on cold weather packages. That won’t cut it in the U.S. So, standard on this (U.S./North American) engine are ceramic glow plugs similar to the Cruze diesel. They will help as they have much higher temperature settings than metallic glow plugs, in addition to a faster light-off.

“But we’re not using integrated pressure transducers to report in-cylinder pressures. We take care of cylinder pressures by calibration,” Yackley affirmed. Also, for cold starting robustness, the motor does have a higher output starter than the global version, and higher amperage battery. There’s an optional block heater available; it’s a wet heater through the side of the block for those extreme below -20 F temperatures. The heater is attached through a cast-in port and it can be retrofitted through the block plug if you later buy a used truck that didn’t ship with one.

Because of cold temperatures, as most of the Midwest experienced this winter, the powertrain includes active return fuel heating. That is, it returns fuel that has been through the line and fuel rail back into the tank to warm remaining fuel. Yackley, like every other key diesel engineer we’ve interviewed, says that diesel fuel in the U.S. is not as good as what you find in the rest of the world. Not only is the sulfur higher, sporadically so, the cetane is much lower and also highly variable, and in the U.S. we can get water in the fuel as well. He says “We have to calibrate for the lower cetane and accommodate the other issues.”

Okay, you’ve gotten this far and you want to know the power you can expect. We don’t have a precise answer for you. Global engines are promised to make 200 hp at 3,600 rpm with 500 Nm @ 2,000 rpm or 369 lb/ft of torque. We’d like to believe the 2.8 will have 400 lb/ft of torque, but won’t bet on it. Yackley tells us why.

“The engine? We’re not releasing numbers, but we expect (Canyon and Colorado) to be the segment leader for torque, towing, and payload and fuel economy. The diesel in particular we expect to exceed. And additionally we have changed the torque curve; it’s lower, optimized for the market and (we have) extended the range. So if you look at the curve for the global engine, (the U.S.) engine will have a longer max range—the 90% range is extended. Definitely, when you drive it you always have torque available whether 0-60 or 40-70 mph. Especially at altitude, we’ve made sure you’ll have torque at altitude.” DW

Future Applications

GM Half-Ton Diesel Soon?

We like making wild guesses, like when we predicted GM would have small diesels by 2015 despite strident denials. So here goes more wild speculation.

The 2016 (late 2015) 2.8-liter diesel will be top dog for towing and heavy duty hauling in the mid-sized truck market unless Chrysler slips the VM Motori 3.0-liter into the Dakota. Base curb weight for the Canyon varies from 3,944 — 4,266 pounds. It has automatic all-wheel drive or two-wheel drive variants announced for both trucks. They have maximum payloads of about 1,400 pounds and tow capacity of 6,700 pounds with their six-speed automatic transmissions.

What else does that fit, understanding that this is “strictly” a truck engine and the current 2.0-liter slots into cars. (It never occurs to us that GM might have a similar I-4 or V-6 car diesel design in the offing to compete with luxury brands like BMW, Audi or Mercedes-Benz, all of whom offer I-4 and V-6 diesels in North America). So let’s look at current classes of GM SUVs and CUVs like GMC Terrain, Buick Encore, Chevy Equinox, GMC Acadia, Chevy Traverse and Tahoe, or Buick Enclave. Let’s even go out on a sturdy limb and think about Silverado and Sierra single cabs. Let’s simply look at the numbers for base engines and see what we think.

As you see, the new 2.8-liter motor packs powerful torque, even against the newly upgraded small V-8s GM is widely respected for. Horsepower, not so much. So let’s say that perhaps there would be a useful application for the diesel in every vehicle except a Silverado or Sierra. Everywhere else that GM has a V-6 SUV or CUV, the 2.8 diesel could easily be packaged as an upgrade for towing, with its greater torque.

Hmmm, that would seem to include a possible use in the Silverado 6-foot bed regular cab. Now we’re not chassis engineers and the payload and tow rating may be more about frame rails, springs and dampers, anti-roll bars, spindles and wheel bearings.
However, a Terrain Moab Special or Equinox Silver Buckle with a suitably tweaked transmission might have merit for horsemen and ranchers. The torque would get down the road and up the hill, and diesel’s efficiency would deliver far better fuel economy under heavy load.

Overseas, one of the first fitments for the new engine will be a Chevrolet Trailblazer. While no longer sold here, that implies it might do well in a Chevrolet Traverse (or Buick Enclave, GMC Acadia) where it would, again, provide more fuel economy with similar, if not greater, tow capacity. But would it get up the freeway ramp as quickly as required?

How about a Tahoe with the smaller diesel engine? On paper it has similar torque, though down a whopping 155 ponies. Could it be packaged as a salesman’s special, a high-mileage people hauler? Surely it has a shot as CAFE ratchets up the mpg. Add an eight- or 10-speed transmission and who knows?