A recent trend in the trucking industry reveals surprising results. In 2009, 56% of all US Class 8 trucks spec’d engines were greater than 13 liter, (a.k.a. big-block or big-bore engines), but as of 2016, that number has fallen to about 40%. The reason for this may be that fleets that prioritize efficiency and lighter-weight trucks are finding that spec’ing a smaller engine with high HP and torque ratings gets the job done.
Mack Trucks does not offer a 15L engine, but touts its 13-liter MP8 engine, which boasts up to 505 HP and 1860 ft./lbs. of torque—comparable numbers to the typical 15L engine. From an engineering standpoint, Tim Wrinkle, Mack’s construction product manager, says there are a couple of changes, which can be made to bridge the gap between 15L engines and 13L engines without sacrificing power. Wrinkle highlights Mack’s use of 14 flywheel bolts rather than 12, more robust connecting rods to evenly distribute peak cylinder forces and the durability provided by its cast-iron block.
The integration between the MP engines, the mDrive transmission and Mack’s axles, Wrinkle says, is one of Mack’s biggest advantages. Mack’s 13-speed mDrive transmission can serve as a compromise option between 18-speed and 10-speed transmissions for heavy-haul operators who want fewer gears to churn through, but without the big drop in RPMs that comes from a 10-speed.
“When you’ve got a heavy load, you need to get that momentum, and that RPM drop is hurting your performance and your efficiency,” Wrinkle says.
Mack’s mDrive HD transmission has an available heavy-haul mode (for 150,000-plus lbs.) with aggressive shifting strategy and less skip shifting, and can go up to 220,000 lbs. This, Wrinkle says, enables you to build momentum and get up to speed quickly without losing those needed RPMs.
A 13L offering leveraging advanced integration can work for fleets—but as evidenced by that 40% mark—a large number of fleets prioritize power and are opting for a 15L engine to tackle their tasks.
Cummins recognized that different applications have different priorities when developing its X15 big-block engine series, which was released last year. The engine maker introduced two specialized version of the engines, both with different priorities: The X15 Efficiency Series engine platform was designed with fuel economy in mind, while the X15 Performance Series was engineered with an emphasis on providing high horsepower and low-end torque for fleets that need the power.
“The key is being able to offer multiple solutions to a broad range of customers,” says Clint Garrett, the Cummins X15 product manager. “Cummins offers multiple heavy-duty options with our 12L and 15L engines, optimized to meet the diversity of customers’ needs.
“In an increasingly competitive industry where fleets need to do everything in their power to minimize operating costs,” Garrett continues, “power solutions tailored to meet specific requirements are a big key to customer success. The Cummins X15 has both the Efficiency and Performance Series engines, offering nearly 30 different ratings, plus hundreds, if not thousands, of ways to further optimize to customer specifications.”
Fleets of all sizes and needs always value efficiency, and there’s no denying that greater efficiency can be found when the components of the powertrain are integrated and built to work together.
When it comes to powertrain integration, the Cummins X15 engines also aim for improved efficiency thanks to the SmartAdvantage powertrain collaboration with Eaton.
“The SmartTorque2, SmartCoast and Predictive Cruise Control features work together to create fuel economy improvements of up to 6% over the base engine [when spec’d with the Eaton transmission]. Moving forward, we are excited for closer collaboration and partnership in our new joint venture,” Garrett adds, referring to the Eaton Cummins Automated Transmission Technologies joint venture to manufacture automated transmissions for heavy- and medium-duty trucks, which the two companies announced this spring.
