Under the Skin: A Closer Look at GMC's Light-Duty Pickups
We recently had the opportunity to sit down with several of the engineers who were behind the development of the new GMC Sierra. While they didn't let us in on any trade secrets (yes, we tried), they did tell us some of the reasons why they made the decisions they did with the new truck, and they talked about some of the features they considered and eventually decided against.
Development of the truck began in about 2009 in conjunction with the development of the Yukon family and the Sierra HD. The team is very tight-knit, and several of the people who worked on the 2014 Sierra also worked on the GMT900. Some of the engineers have been working on GM trucks since the GMT400 project, and a few have GM truck experience that goes back even further. Though there is a lot of tradition behind the trucks, the team was well aware that when it comes to the development and advancement of pickups, things are moving faster than ever. Jeff Luke, executive chief engineer for global full- and midsize trucks and SUVs, said, "The rate of change is ever-increasing, whether it be a customer requirement or a government regulation for fuel economy standards. So change is happening around us all the time. We need to be able to be flexible and adaptable, and to make sure we have products customers are looking for."
For that reason, GMC made many big changes between the GMT900 and the K2XX platforms. Though the engines have the same displacements as those they replaced, they are new and are part of the same engine family that powers the Corvette. The EcoTec3 engine family possesses three key technologies: direct injection, continuously variable valve timing, and Active Fuel Management.
Sheryl Balsley, assistant chief engineer for the EcoTec3 family of engines, explained how AFM works, especially when ensuring that the engine is in the right mode for the demands being put on the truck: "The electronics in the computer detect when the engine is in the right condition to run on a four-cylinder mode. There are solenoids that will deactivate the lifter mechanism and then will shut off the lifters for cylinders three and six on a V-6 or cylinders one, seven, four, and six on a V-8."
It was more of a challenge getting AFM to work on a V-6, but as Balsley explains, "The V-6 does have a counter-rotating balance shaft in there for the NVH requirements of the engine. From day one, we worked closely with the vehicle team to determine which cylinders to shut off. We had to make sure that, when we made the selection, we did it from a noise and vibration perspective that was the best for the application."
AFM has been used on GM trucks for several years, but this is a new evolution of the system, and adapting AFM to an overhead-valve engine is in some ways easier than with a DOHC engine, because it can go on one camshaft in the valley of the engine. It also helps keeps complexity -- and cost -- down. The engineers also take pride in the legacy of small-blocks, a part of GM trucks since 1955.
All three engines use new blocks and heads. The engines use a cam-driven fuel pump, and making it work required many changes to the block. It made more sense to go with an all-new block with the structural improvements the team wanted. This also served as an opportunity to optimize the combustion chamber for direct injection.
The team spent 10 million CPU hours of time of computational analysis designing the new family of engines, with 6 million of those hours on the combustion system alone. When all was said and done, there were only a couple nuts, plugs, and maybe one sensor shared with any of the previous engines. While the ideas of improving efficiency and reducing friction may not sound all that exciting, the result is increased power and torque and improved fuel economy.
When it came to designing and updating the truck bed, there were a lot of factors at play as well. GM knew full well that the cargo box would be used for hard work and recreation, so the goal was that the bed should not offer only the capability -- volume and payload -- an owner wants, but also ease of use. That's why the bed is available with the CornerStep bumper, which allows you to access gear whether the tailgate is up or down. There are built-in grips, as well as standard upper tie-downs that an owner can move to nine different locations on the bed. Each tie-down can withstand a 250-pound load. This replaces the previous generation's cargo management system, which was not a huge seller. LED lights under the bed rails can light up the bed, and an EZ Lift and Lower tailgate that uses a torsion bar and a rotary damper to make the tailgate easier to use are also available. An anti-chip coating sprayed on the bottom part of the pickup box, under the paint, prevents corrosion should the paint chip. There are also stone guards behind the rear wheels. The bed itself is constructed of roll-formed steel, which allows the team to use thinner gauge, high-strength steel. The team considered using aluminum in the bed, but chose not to because of the cost of materials and repair and the fatigue life of aluminum.
Because customers wanted a choice, spray-on and drop-in bedliners are available. A tailgate lock is now standard, and the rear camera and parking assist were added to make it easier to line up the truck with the trailer.
Another interesting thing we learned: The engineers factor livestock into the design of the cargo box and tailgate. They have a "hoof load test" to make sure the open tailgate can withstand a steer's weight when it steps into the bed.
For more information about tow-testing the trucks, we spoke with Robert Krouse, GMs trailering engineer. He designed the trailer hitches and coordinates the activities that go into trailer weight ratings and GVWR. Since trailer towing involves so many different elements -- powertrain, braking, handling, etc. -- the team uses tried and true testing to develop trailering specs. They test in the Southwest desert, and on grades such as Davis Dam in Arizona, for grade ability and thermal performance. They do specific handling maneuvers and brake tests, and they evaluate technologies such as trailer sway control and hill start assist at GM's proving ground.
To increase towing capacity for the new truck, GM improved the thermal system and enhanced the suspension -- and, of course, the added horsepower and torque helped too.
Regarding J2807, Krouse, who heads the SAE Tow Vehicle Trailer Rating Committee, said implementing the SAE regulation is still in progress. "What we [the committee] plan now is the manufacturers will implement it as they are ready. Several want to do it with new introductions. Others are saying when most of the industry is ready, they will follow suit. We are pretty much leaving that up to each OEM." The committee is made up of engineers throughout the industry, so when Krouse spoke about J2807, it was from the perspective of the committee, not as a representative of GM.
Chuck Lemont, a vehicle development engineer who works at GM's Milford Proving Grounds on vehicle acoustics, gave us insight on how the team made the cabin so quiet. He said the body had to be redesigned to incorporate the switch from rolled doors to inlaid doors. But there was a huge payoff: It allowed for the triple seals, which is something you see more in luxury cars, and made a big difference in reducing cabin noise. The dash mat on the engine side of the front dash now has greater coverage; there's better coverage in the acoustic back panel on the back of the truck; and the new headliner was designed to absorb more noise. They had to deal with the idea of "draining the swamp," where once you dramatically reduce cabin noise, you start to hear things you didn't hear before. As an example, the rest of the sound reduction was so good, engineers heard noises from the HVAC module they hadn't heard before. Something that previously would have been a slight squeak or rattle was suddenly noticeable, and had to be taken care of.
Braking upgrades focused on performance and reliability. While the front discs are a hair larger than before, the rear brakes have gone from 11.6-inch drums to 13.6-inch discs. When we took the Sierra to the track for performance testing, we observed that the 2014 needed only 125 feet to stop from 60 mph -- the previous generation took 150 feet to stop from 60. The brakes were also designed to be quieter and work with less vibration. Also, these brakes use Duralife brake rotors, an innovation first used on the Cadillac DTS, with a surface strengthened by a system called ferritic nitrocarburizing, where nitrogen and carbon are diffused into to the rotor, hardening it. Another benefit of this process is corrosion resistance. GMC anticipates these rotors could last twice as long as conventional rotors.
The 2014 Sierra team is filled with experience and enthusiasm. Many of these engineers have been working for the company for several decades, almost all in truck development. These are also the people who had been into cars and trucks as kids. One engineer mentioned that he took his dad's lawnmower apart to see how it worked, then was mostly successful at putting it back together. The team behind the new truck understands the needs of truck people, thanks to a combination of customer input, research, and experience, and put all that into the new models.
MEET THE TEAM
GMC's engineers were happy to talk about the Sierra.
GMC's engineers were happy to talk about the Sierra.