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."
What better way to examine the new components of the Sierra than by going to the assembly
GM's Duralife brake rotors are designed to last longer than standard rotors.
The EcoTec3 engines use all-new technology to improve performance and fuel economy.
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.
Here you can see a Double Cab being assembled, as well as the cab as it goes along on the
One of the biggest changes to the new Sierra is the switch to inlaid doors from rolled doo
One of the biggest priorities with the new Sierra was to make it easier to get work done.
Customer feedback led to the implementation of the CornerStep bumper, as well as the EZ Li
The box and tailgate also had to pass the "hoof load test."
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.