11-,12-Liter Engines Growing Up
This story appears in the April 11 print edition of Equipment & Maintenance Update, a supplement to Transport Topics.
Not that long ago, the mindset of many fleet operators was to get as much muscle power in engines as they wanted or could afford. That often meant 15-liter engines that could deliver a whole lot of horsepower. But times have changed.
With evolving technology and additional greenhouse-gas emissions and fuel-economy regulations pending, smaller engines are becoming more common — not just 13-liter models but also those in and around the 11- to 12-liter range.
In early January, Paccar Inc. upped the ante by installing in the United States its first production MX-11 engine, a 10.8-liter power station. It went into a Peterbilt Model 567 for North Dakota-based fleet Knife River, one of the largest aggregate producers and suppliers of concrete and asphalt in the United States.
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The move by Paccar followed the 2013 launch of the MX-11 in Europe, where it has installed more than 10,000 of these engines in trucks made by its European operation DAF. The MX-11 is built at Paccar’s engine manufacturing facility in Columbus, Mississippi, along with the MX-13.
Paccar isn’t alone when it comes to having engines in and around 11 to 12 liters, with offerings in the United States from Cummins, Navistar, Volvo and Mack.
So what’s driving the trend toward smaller engines? Several factors.
These engines aren’t new, but the power they deliver is much more than it was, even just a few years ago, said Charlie Cook, marketing manager for vocational products at Peterbilt, which is owned by Paccar.
“We are able to achieve more horsepower and torque with less displacement,” he said. “We are getting 430 horsepower and 1,550 pound-feet of torque out of the new MX 11-liter engine, something that a few years ago would have required a much larger engine.”
More technically, this means several things, said Mario Sanchez-Lara, director of on-highway marketing communications for Cummins, which makes the 11.9-liter ISX12 model engine.
“Increased power density is the objective, which drives adoption of aggressive compression ratios, increased injection pressures and higher fresh air induction,” he said. “Similar to what we have seen in passenger cars, truck engines are adopting dual overhead cams, variable timing, high-pressure fuel systems, multistage turbocharging and sophisticated materials like compacted graphite iron on the blocks and head castings,” the latter making the engines lighter.
The increasing sophistication of engine control software is helping. Mack Trucks offers the 11-liter MP7 with 325 to 405 hp and torque ratings from 1,200 to 1,560 pound-feet, which maintains what Stu Russoli, highway and powertrain products marketing manager, calls “good efficiency numbers.”
“Integration plays a role, too, particularly in the case of our mDRIVE automated manual transmissions,” Russoli said. “Our MP engines are fully integrated with mDRIVE, sharing 100% of the information 100% of the time.
“Together, they sense factors like the load on the truck, incline, decline, speed and more to get the most performance and efficiency out of a smaller engine displacement.”
In other words, a lot of the move to smaller engines has to do with efficiency. This is why there also are many more 13-liter engines in use today compared with 15-liter ones, said Mike Evans, senior consultant at Rhein Associates.
“The race to add more horsepower has really slowed down over the last 15 to 20 years,” he said. “So now we can do more with less. In the past, you would see lots of 15-liters, and then the 13-liters came in and we saw a trend into 13-liters. That doesn’t mean the 15-liters went away, but a large proportion of that business has moved to 13-liters.”
It’s largely about fuel efficiency, said John Moore, powertrain product marketing manager for Volvo Trucks, which offers a 10.8-liter D11 engine.
“The fuel maps on these engines are optimized for regional haul, less-than-truckload and diminishing-load applications running on flat to rolling hills,” Moore said. ”You can post excellent miles-per-gallon numbers, if set up correctly.”
In addition to technology advancements, helping to drive this trend toward smaller engines are increasing federal emissions regulations, Moore said.
He believes future advances in horsepower and torque will allow these smaller engines to cross even further into their larger-displacement counterparts’ applications zone at increased efficiency.
“Future GHG regulations are requiring dramatic reductions in aerodynamic drag, along with more efficient engines,” Moore said. “Because the hood slopes are more aggressive to lower drag, engine installations at higher displacements become a greater challenge to install within limited space and still have enough space available for technicians to service them.”
Weight savings is another main driver, especially in certain vocational applications “where they are looking to get every pound of payload,” Rhein Associates’ Evans said.
If an 11-liter can do the job and save 400 pounds of weight for a regional or bulk hauler or vocations such as refuse, that helps productivity.
That weight savings is attractive to any operation concerned about grossing out before cubing out, such as bulk and tanker haulers. They also are a fit for local and regional operations as well as construction and refuse.
“I think the regional haulers look to buy the most efficient truck they can,” Evans said. “They don’t need the absolute power perhaps they get from a 13, definitely not from a 15.” When you look at the horsepower and torque ranges the 11-liter engines provide, they get well into the 13-liter applications, he said.
“If the customer is hauling high-cost freight, such as fuel, they will see an immediate payback for the extra 390 pounds they can now haul,” said Volvo’s Moore, who noted the D11 engine is 390 pounds lighter than the company’s 12.8-liter D13 engine. “There aren’t many options on the truck that cost less and save this much weight.”
This is what drove Walpole Inc. to check out the 11-liter Paccar engine, said Keith Walpole, president of the company, a 240-tractor bulk hauler, which also has been running the 13-liter Paccar MX-13 model engine in some of its trucks.
“We have never been afraid of running a smaller cube engine,” he said. “We’re in the bulk-hauling commodity movement business, and weight is our dollars.”
This weight savings with the MX-11 versus the MX-13 is about 400 pounds, which Walpole said has translated into a 5.1% improvement in fuel economy — and more than 12% when compared with larger engines from other makers just a few years ago.
If you worry about not having enough power with an 11-liter engine, but you don’t want the weight of a 13-liter engine, some 13-liters are actually smaller — such as Navistar’s 12.4-liter N13 model, said Steve Gilligan, vice president of product marketing.
The current N13 weighs 2,400 pounds installed in chassis, about 565 pounds lighter than a Cummins ISX15 engine, about 200 pounds less than the Paccar MX-13 engine and 200 pounds heavier than the new MX-11, he said.
“Right-sizing” the engine, as it is called, can be part of an overall “lightweighting” strategy. The North American Council for Freight Efficiency advocates selecting equipment and components that are lighter, allowing for better fuel efficiency and more freight per truck.
“Getting a big number, like hundreds and hundreds of pounds, like you can with these engines, allows you to add some other fuel-economy technologies that are adding weight,” NACFE Executive Director Mike Roeth said, such as aerodynamic add-ons and idle reduction systems.
Looking ahead, those interviewed said that engines in and around the 11-liter to 12-liter range offer more horsepower and torque than ever and are likely to get even stronger. These engines can save you weight, allowing for greater payloads and improved fuel efficiency.
Thus far, they seem best for regional and local operations, depending on the geography, and for bulk and tanker applications, they said.
But these engines aren’t for everybody. Planning on trucking across the Rockies or the Appalachians while loaded up to 80,000 pounds? Chances are your drivers may be cursing your name and thinking about quitting to work as a Wal-Mart greeter.
However, the most crucial thing to consider may be what Keith Walpole said: “The strongest advice I would have is to analyze your current fleet’s data and just see how much horsepower you have been using and how much torque you have been using versus what you are buying, moving forward.” ³
