New Mack Powertrain Improves Fuel Efficiency

July 31, 2012

Let’s say you’ve bought a new Mack Pinnacle tractor and it’s now hitched to a flatbed trailer that’s loaded to the rubrails with lumber or bagged concrete or some other heavy commodity. You’ve told your driver that he should upshift at really low revs—1,400 rpm. Ha ha—of course he won’t drive it that way.

Let’s say you’ve bought a new Mack Pinnacle tractor and it’s now hitched to a flatbed trailer that’s loaded to the rubrails with lumber or bagged concrete or some other heavy commodity. You’ve told your driver that he should upshift at really low revs—1,400 rpm. Ha ha—of course he won’t drive it that way.

You anticipated that, so you’ve spec’d a new Super Econodyne powertrain. Its specially programmed mDrive automated gearbox upshifts early and often, usually at that low-low 14 hundred mark on the tachometer that the driver stares at in disbelief. At first he forces the engine to rev higher, but sees that if he leaves things alone, the rig accelerates pretty well, and it settles into a cruise speed of 62 mph with the engine spinning at a leisurely and quiet 1,160 rpm. He doesn’t like it at first but it grows on him, and you’re seeing some serious fuel savings.

Mack Pinnacle Specifications

  • Truck:2013 Mack CXU613 Pinnacle road tractor w/ setback steer axle, Rawhide trim package, 70-inch Hi-Rise sleeper box, BBC 173 inches, GVW 49,200 lb., GCW 80,000 lb.
  • Engine:13-liter Mack MP8-445SE, 445 hp @ 1,500-1,800 rpm, 1,750 lb-ft. @ 1,080-1,280 rpm, w/ PowerLeash engine brake, Bendix Wingman adaptive cruise control, and Borg-Warner multispeed viscous fan drive
  • Transmission:Mack mDrive 12-speed automated mechanical w/ 17-inch organic-facing automated clutch, 0.78 overdrive and Grade Gripper hill holder
  • Steer axle:12,000-lb. Mack FXL12 on taperleafs
  • Tandem:37,200-lb. Mack S125/126 double-reduction w/ 2.66 ratio, on Mack AL401 air-ride
  • Wheelbase:215 inches
  • Fifth wheel: Jost JSK37UWL w/ 24-in. slider
  • Tires & wheels:275/80R22.5 Michelin XZAG+ front, 445/50R22.5 Michelin X-One XDA rear, on Alcoa polished aluminum discs
  • Brakes:Bendix S-cam drum w/ Bendix ABS
  • Fuel tanks:Twin 117-gal. aluminum
  • Demo trailers:48-foot flatbed and 53-foot van

That’s the idea of the Super Econodyne concept, says Dave McKenna, director of powertrain sales and marketing at Mack Trucks. Drivers who do things the wrong way can kill fuel efficiency, so take away those decisions from him and, by default, he’ll do things the right way. In his 39 years with the company, McKenna has seen the old high-torque-rise Maxidyne and many other iterations on the quest for top fuel economy. And he knows that, properly engineered, a diesel can lug down low without its valves burning or pistons cracking or any other damage.

“Nobody wants to run at 1,160 rpm,” said McKenna of disbelieving drivers and owners. “They’ll say, ‘I can’t do that. I can’t do that.’ I’ll tell you what: It’s my engine. If it blows up, I’ll rebuild it.” The warranty on the engine, by the way, is two years or 250,000 miles.

To encourage skeptics to try the concept, he’s made Super Econodyne (SE) a no-cost option for anyone buying its all-Mack components: a 13-liter MP8 engine set for 455 horsepower and 1,750 lb.-ft.; a 12-speed mDrive automated mechanical transmission with a 0.78 overdrive top gear; C125-series double-reduction tandem rear axles with a 2.66 ratio; and 11R22.5 tires (though demo tractors had wide-base single rear tires and wheels). This is a gear-fast, run-slow specification; while the gearing allows a top speed of 95 mph(!), the SE’s electronic controls were programmed to enforce the “slow”—70 mph while in cruise control and 72 mph tops.

The operating difference between a standard MP8-455 and an MP8-455SE is about 200 rpm, McKenna explained during a mid-June press event at Mack’s old technical center, now its Customer Service Center, in Allentown, Pa. Super Econodyne is a highway tool and is not meant for vocational trucks, though haulers of bulk cement, rock and building supplies might well utilize it. Later, there’ll be an 11-liter SE that’ll weigh about 300 pounds less than this 13-liter model, McKenna said.

After a briefing, writers who had never driven a tractor-trailer could safely take the two demonstration rigs onto the adjacent 3/4-mile test oval because the mDrive self-shifting trannies made driving easy. A few of us have commercial licenses and had driven a bunch of trucks, so were qualified to go out onto nearby Interstate 78, and did. After about 50 miles on the I-road, I came away impressed with the Super Econodyne’s operation, and the quietness and comfort of the Pinnacle tractor.

I drove both demo tractors, one hitched to a flatbed laden with heavy concrete blocks and the other pulling a van with a similar load for ballast. Each rig weighed close to the 80,000 pounds for which the SE system is rated, so the MP8 engines had to work to keep us moving. I took both around the test track, watching the SE “short-shift” the tranny at 1,400 under a light foot on the go pedal, but letting revs climb to 1,600 or 1,700 if I floored it, and as much as 2,000 rpm if I punched the PERF (performance) button on the mDrive’s “premium” keypad selector. It also has up and down arrows to call for up- and downshifts.

Neither the PERF nor the arrows are on the standard “fleet” keypad to keep drivers from forcing the engine out of its efficient, low-revving range, McKenna had said. Take away those options and the driver simply must let the engine and transmission work as they’re supposed to, whether or not he agrees. For example, some drivers want to downshift on downgrades to get more retarding power from the engine brake, but they won’t be able to with the standard selector.

When I was finished on the track, my guide and powertrain sales manager, Joe Scarnecchia, directed me out onto city streets toward I-78. “You turn right just up here,” he said, and I did—one corner too soon, which caused me to blunder into a Home Depot complex. I headed toward the rear of the building—“Yeah, we can just go around the back”—only to find a rig blocking the entire alley so its driver, who wasn’t around, could unload some building supplies. What a jerk, I thought. So I backed up a short block and maneuvered through the parking lot to get us to the on-ramp. I can tell you that the mDrive’s automated clutch eased this chore and the Pinnacle’s setback steer axle has a nice, small turning circle that allowed some sharp turns in tight places.

Finally on westbound I-78, I watched the tach as the short-shifting continued, even in high-range gears as we got up to cruising speed. And just as McKenna had said, the revs were low, about 1,100 at 60 mph and 1,200 at 66. Strong torque kept us well propelled on the level stretches, but on moderate upgrades our road speed usually fell off by 5 mph, just as it would when you keep a manual tranny in high gear while climbing hills. This has to do with the laws of thermodynamics meeting the law of gravity: To maintain speed on hills, you need horsepower that only comes from higher revs. I got this by either stomping on the accelerator or hitting PERF and hoping the mDrive would react with a downshift, which it usually did.

The SE package comes with cruise control, Bendix’s latest Wingman “adaptive” type, which uses forward-looking radar to sense what’s in the lane ahead and adjust speed accordingly. If a car up there is moving more slowly, it reduces the throttle to let the rig slow down, then reapplies power when the traffic ahead speeds up. This is neat except that on one occasion it harshly reapplied the throttle, banging the driveline, and did it twice in short succession.

Wingman also applies the brakes if the rig is closing in too fast on something ahead. It usually does this appropriately, with gentle applications, but once it suddenly jammed on the brakes. “What is that?!” I asked Scarnecchia, who was as puzzled as I. A Canadian colleague of mine earlier had reported similar disconcerting behavior with Wingman on a Volvo tractor, and now I saw what he meant. We have made Bendix people aware of this and hope they are working to smooth out the programming. Meanwhile, the solution is to turn off cruise control in traffic, which is a good idea anyway because an alert driver’s eyes can see things that radar cannot.

Volvo, Mack’s sister company, introduced a similar low-rpm concept last year. It’s called XE, for Exceptional Efficiency, and uses the I-Shift automated transmission with 13- or 16-liter engines. Bite your tongue if you say that these products are the same as Mack’s, because McKenna and other executives insist that electronic controls on the mDrive as well as all Mack engines are carefully programmed to deliver unique operating characteristics. In this case, the outcome is the same—better fuel economy by 5 percent to 10 percent, according to test fleets, and a relaxed driving experience that you might grow to like.