On the Road to Cracking 10

I have developed a new appreciation for drivers who post consistently high fuel economy numbers, especially those already in 8- to 9-mpg territory who push every day to crack 10. A lot of discipline and hard work goes into that kind of performance, but their trucks also deserve a good chunk of the credit.

In September, Mack Trucks invited a handful of truck writers on a three-day adventure tagged the "2018 Mack Trucks Performance Tour: Gears, Guitars & Grub." It was intended to be a demonstration of the latest Mack engine technology, but it quickly turned into a fuel economy contest of sorts between the CDL-holding editors:  Steve Bouchard of Transport Routier, Jason Cannon of Overdrive, James Menzies of Truck News, and yours truly.

The additional drivers were all Mack people, including Scott Barraclough, technology product manager; Phil Cary, Southeast regional fleet service manager; Curtis Dorwart, refuse product manager; Roy Horton, director of product strategy; Stu Russoli, highway marketing manager, and Tim Wrinkle, construction product manager.

A few of us also pitted our facial follicles against our colleagues to see who could grow the best trucker beard in four days. Bouchard won that one handily. He didn't do badly in the fuel economy challenge, either.

The trip began in Asheville, N.C., just two days after Hurricane Florence clobbered the coastal regions of the Tar Heel State. More than a few of us weren't sure we'd even get into the Charlotte airport to make our connections to Asheville. That town, in the northwest part of the state, was high and dry relatively speaking, so come Monday, the game was on.

The organizers, Kim Pupillo and Christopher Heffner of Mack's communications department and their team, had laid out a 930-mile route-- from Asheville to Nashville on Day 1; from Nashville to Memphis on Day 2, and from Memphis to New Orleans on Day 3. True, we weren't exactly pushing the hours-of-service limits, but they were decent days for a bunch of desk jockeys. And naturally, there were a few nice restaurants we just had to stop at along the way, like Rhubarb in Asheville, the Southernaire Market in The Guitar, the Blues City Café on Beale St. in the "Barbecued Pork Capital of the World," and finally, Antoine’s Restaurant in The Big Easy.

While in Nashville, we were treated to a command performance in a small studio setting by recording artist Steve Moakler, the fellow who sings the Mack Anthem theme song, "Born Ready."

It's a tough job, dear reader, but somebody had to do it.

As technology demonstrations go, this one was both fun and revealing. Mack assembled a fleet of six trucks for the tour, two each of a particular pedigree. Journalists drove a different truck on each leg of the trip to get a feel for the technology and post their best fuel economy numbers.

As I'll explain, the performance of each of the truck pairs turned out to be similar, regardless of whose foot was on the pedal. That showed me there's a level of consistency across the technology-matched trucks when operated in cruise control where the truck and the onboard systems are making most of the decisions.

The trip began in Asheville, NC and wound up in New Orleans, LA. The first leg was Asheville to Nashville along I-40, a distance of about 300 miles. We passed through Great Smokey Mountains National Park early in the day with a good share of mountain grades and rolling hills. The road leveled out to gently rolling hills once we cleared the Park, and the profile remained more or less the same all the way into Nashville.

Leg two was Nashville to Memphis along I-40, a distance of about 220 miles. The road profile was gently rolling hills, though somewhat flatter than the previous day.

And Leg three was Memphis to New Orleans along I-55, a distance of nearly 400 miles. There were some modest hills on the northern section, but it flattened out south of Batesville and remained pretty flat all the way to the Gulf.

Each of the trailers were loaded the same way, giving us a gross vehicle weight of 65,000 pounds, give or take a few hundred.

The Trucks

Most of the componentry on each truck was identical, including tires, brakes, fuel tanks, interior packages, etc. Each featured a Mack MP8 engine and an mDrive 12-speed overdrive (0.78:1) automated manual transmission. The engines specs varied by pair along with some additional fuel-saving options.

Trucks 1 & 2 (the baseline models) had the full Anthem aero package, while 3 & 4 and 5 & 6 had the HE+ (high-efficiency) aero package, which included a roof fairing with trim tab, extended side fairings, chassis fairings with ground effects, and an aero bumper with a spoiler.

Tractors 1 & 2 (red):

• Mack Anthem 70-inch standup sleeper 6x4
• Engine: Mack MP8-445C, 445 hp/1,860 lb-ft
• Rear axle ratio: 2.47:1
• Full Anthem Aero

Tractors 3 & 4 (white):

• Mack Anthem 70-inch standup sleeper 6x2 liftable pusher axle
• Engine Mack MP8HE-415SE, 415/1,760 with ERT*
• Rear Axle Ratio: 2.50:1
• HE+ Aero

Tractors 5 & 6 (blue):

• Mack Anthem 70-inch standup sleeper 6x4
• Engine: Mack MP8HE-445SE, 445/1,860 with ERT*
• Rear Axle Ratio: 2.47:1
• HE Aero+

*The MP8HE engine employs Mack's Energy Recovery Technology, which is essentially a turbo compound system. It uses engine exhaust to spin a turbine, capturing otherwise wasted energy, which is then routed back to the engine via a gear train and a hydraulic coupler. The magic of this design is that it's optimized for low-rpm energy recovery. There are two significant benefits to this approach,  instead of adding the additional energy as higher horsepower at the top end.

First, the energy added by the turbo compound manifests itself as additional torque, which is very useful in a downsped drivetrain. Second, and most importantly, the input of that additional torque helps smooth out the torque spikes produced by high-energy, low-rpm engine operation.

Every combustion event sends a spike of power through the driveline, which if it's not managed can damage driveshaft U-joints and axle pinion gears. It's like pounding on them with a big sledge hammer. This turbo compound design minimizes the impact of those torque spikes and allows for very low rpm engine operation for prolonged periods with little or no risk of driveline damage. As you'll see, I spent some time operating the engine at just 875 rpm on shallow rolling hills.

I believe Mack's HE ERT feature was instrumental in bumping up the fuel economy numbers on the trucks equipped with it, as it allowed lower engine speeds than the non-HE MP8 engines.

The Results

Every truck managed at least 8.0 mpg over the three-day trip (see chart: Truck Grand Total). Only one truck fell below that in the daily totals, hitting 7.9 and 7.8 on the first and third days, respectively, with the same driver. On the 2nd day, with an editor at the wheel, it managed 8.5, so we're not going to fault the truck, but we did have a talk with its driver.

The baseline trucks in our test, the red trucks (see specs above), averaged 8.0 mpg over the three-day 930-mile trip. The blue trucks averaged 8.4 (4% better than the baseline), and the white trucks averaged 9.2 mpg.

The white trucks were spec'd to be the most fuel efficient with a combination of a 6x2 powertrain, a lighter engine spec, Mack's Energy Recovery Technology (turbo compounding) and the advanced aero package. They clocked in at 14% more efficient than the baseline trucks. That's quite a jump in my opinion and I'm currently digging into why that might be.

Curiously, Truck 4 was consistently 1.4 mpg better than Truck 3, yet the two were identically spec'd and the fuel-burned and miles-run numbers all work out. It should be noted that both those trucks ran about 13 miles further than the rest of the fleet. That's because they both missed an exit on Day 1 and had to double back.

I recorded 10.4 mpg on Day 2 with Truck 4. A day earlier, Steve Bouchard managed 9.8 mpg with that truck while James Menzies posted a 9.8 on Day 3.

Still, 1.4 mpg is a huge gap between two identical trucks. It could be explained by the fact that the trailer tails did not automatically deploy on some trucks on some legs, but I'm not aware which trucks were affected. There may also have been differences in the tractor/trailer gap or the tire inflation pressures. The average speeds for the two trucks over the trip were similar, 51.5 and 52.5 mph, with Truck 4 posting the lower average speed. Could that account for a 1.4 mpg difference?

That said, any truck that will cruise at 8.5. 9.0 or even 10+ mpg right out of the factory is doing something right.

The truck all drivers did their best fuel mileage on was Truck 4, the 6x2 with the MP8 SuperEconodyne with the HE+ calibrations and the turbo compound Energy Recovery Technology. It had had lower horsepower and torque ratings than the other two trucks (415/1760 versus 445/1860) but a slightly higher rear-axle ratio (2.50 versus 2.47). There are some minor efficiencies to be gained from having a single drive axle, as you lose the parasitic drag and weight from the additional drive axle in a 4x6 setup. Mack's 6x2 used load-biasing to improve traction on the driving axle, so the weight on the pusher might have been a little less, which might have reduced the rolling resistance from those tires, but not significantly.

At a cruise speed of 65 mph, the engine was turning a remarkable 1080 rpm. Peak torque on the engine goes down to 950, so at cruise there's still a little room before you'd need to downshift. At 62 mph, the engine turned just 1030 rpm. As I explained earlier, the low engine speed is possible because the turbo compound smooths out the torque spikes that occur at low engine speed and can damage drivelines.

At highway speed on flat ground, the engine load was running around 60%. When we started pulling grades, I tried to limit the engine load to not much more than 80% by backing off on the throttle, rather than letting the cruise control jack up the engine load to 100%.

It's a brilliant spec for a truckload application running predominantly on flat or rolling terrain, and the fuel economy numbers we achieved corroborate that.  

As an aside, I measured the noise level in the cab with a sound meter app on my iPhone and got really low readings of 64 dB in a coast and 67 dB in a pull -- virtually the same as the Kenworth W990 we drove a couple of weeks later in Las Vegas.  

Now let me explain what 10.4 mpg really represents.

We spent most of the run in the top gears where the engine is most efficient, and only a few miles wheeling through town and in parking lots in the lower gears where I saw numbers on the display screen like 2.5, 4.0 and maybe 5.0 mpg. To illustrate the point, as I exited the highway at Memphis and headed for the dealership there (in Truck 4), the MPG screen showed 10.6. By the time I shut off the truck at the dealer about two miles later, it was down to 10.4.

The numbers revealed here are really just for a single leg of a trip with very few off-highway miles, and almost no idling. Drivers who can post fuel economy numbers in the high 8s, 9s and even 10s over a full month -- with more idling and stop 'n' go operation -- are truly heroic and extremely disciplined operators. I tip my hat to them.

Cracking 10

I have to say I feel pretty good about my 10.4 mpg leg on Day 2. But I also have to acknowledge that my two colleagues, Bouchard and Menzies, each got 9.8 on their rides in Truck 4. They are both great truck writers, and I'd grant average truck drivers. I think they could both get driving jobs today if they wanted them. But not to discredit them, I'd guess they have no more than 20,000 miles between them. My point is, I have 20 years of experience coaxing higher mpg from trucks and these two upstarts come along and get uncomfortably close to my fuel mileage.

Speaking with them afterwards, I learned that they both used cruise control more than 80% of the time, so the truck was doing most of the heavy lifting. That tells me Mack has done an extraordinary job of packing their ECM with all the right algorithms to maximize fuel efficiency. The High-Efficiency aero package obviously added to the success of the truck. Even the blue trucks, Trucks 5 & 6 with Energy Recovery Technology, did a better job at saving fuel than the baseline model. Again, Mack has backed a winning technology with turbo compounding.

As for me, I sort of tipped things on their ear by not using the cruise control and managing the driving process myself. My time in cruise was just over 30%.

That approach netted me the high average mpg for the tour at 9.5, and the best out of three drivers on Truck 5 at 8.9 mpg. Full-disclosure here: the truck I was driving on Day 3, one of the baseline models, broke down so I couldn't complete the mission. My high average fuel economy did not include a leg on one of the two least efficient trucks. However, I will say that my fuel economy on that truck, 45 miles into the trip before a low-fuel pressure warning shut me down, was 8.2 and climbing -- right up there with Bouchard (8.3) and Menzies (8.1) on the same truck.

It was later discovered that. as Mack told me, a "faulty fitting in the fuel supply system leaked, causing air to be drawn into the system." 

My fuel saving strategy has always been to use very gentle throttle input and avoid going to full power on the engine whenever possible. I'm a disciple of the Jim Booth school of driving. Booth is a former test driver with Caterpillar who, even 15 years ago, routinely posted double-digit fuel economy numbers. 

I made good use of the driver's display screen that showed percentage of engine load. In days gone by, that would have been analogous to either the pyrometer (exhaust temperature) or a turbo boost gauge (intake manifold pressure). Keeping any of those readings as low as possible means you're burning the least amount of fuel possible.

In the case of the engine load display, when the cruise control was engaged, the engine would spool up to 100% when climbing and maintain 100% until the truck got to the top. By modulating the throttle and trying to keep the engine load below 80%, and then backing out of the throttle as the grade leveled out near the top, I'd go over the top at 50 mph rather than 60, for example. Gravity did all the work getting me back up to speed on the way down.   

I ran a few uphill segments with the cruise control on, and it appears Mack has set some parameters the keep the engine in low power demand for longer than traditional cruise control would, but it always hit 100% at some point in the climb.

The "problem" with cruise control is that it wants to maintain a set road speed and so it fuels the engine and shifts the transmission accordingly. Mack's GPS-based predictive cruise control system does a pretty effective job of managing road speed based on terrain, but while I controlled the fueling and the shifting, I could get the engine revs to drop lower than the cruise control wanted to go. For example, on the two HE-equipped trucks I drove, and particularly the 6x2 with the 415/1,760 MP8 engine, I had the revs as low as 875 a few times climbing a hill, just by feathering the pedal and trying to prevent a downshift.

I'm talking rolling hills here, not mountains. On long grades, 100% power was the order of the day. But when I had a chance to roll back the power a little on a hill, I did it religiously.

And because I would crest the hill at a lower speed, I didn't hit the engine-brake-on trigger speed quite so soon on the way down, which gave me more opportunity to use gravity rather than fuel to get back up to speed. Mack does have a variable engine-brake-on-speed setting that the driver (or fleet) can set to provide more free-rolling time.

About the only time I engaged the cruise control was to coax the transmission to drop out of gear for a little free-rolling time.

If you spoke with Bouchard, Menzies, or Jason Canon they would tell you the trucks, in addition to being very fuel efficient, were also very drivable. Mack has done well in designing the Anthem with a very efficient powertrain that doesn't lack performance.

Although I beat the Anthem's cruise control system by about half a mile per gallon, I'll be the first to admit that any truck designed to operate the way I was driving that day would probably make a lot of drivers crazy. But frankly, I can't understand why any driver who buys their own fuel wouldn't drive like that.

The clincher was on that 200-mile leg, I arrived at the destination just 10 minutes behind everyone else. But at 10.4 mpg, I beat most of the other trucks by a full two miles per gallon, and the second-best truck by 1.5 mpg. I have always said the winner of the game is not the driver who gets to the bank first on payday, but who gets there with the biggest deposit.

A hearty thanks to Mack for setting up the Gear, Guitars & Grub Performance Tour. It was a great way to demonstrate the company's advances in aerodynamic design and engine technology. And it was a whole lot of fun, too.

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