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Small Block, Big Performance

Posted: August 1, 2014 by Jim Park

When Mack’s Walter May and Win Pelizzoni co-designed the Maxidyne constant-power profile in 1967, they set a standard for engine performance that endures today.

Incorporating high torque at low rpm and smooth transition to higher horsepower (relatively speaking: 237 hp, 860 lb ft at the time), the two engineers gave the engine a distinct personality that set it quite apart from other brands, giving Mack engines a sort of performance trademark.

Dyed-in-the-wool Mack customers worried that might be lost when the company announced it would be tapping into a “new family of Volvo Group engines” to meet EPA’s 2007 regulations. The basic architecture of the two engine lines was to be more or less the same; block, pistons, crank, gear train, camshaft, etc. The differences would come from the ECM-the electronic controls of the engine. The “differences would be more obvious than the similarities,” we were told.

You know what? They were right. The May/Pelizzoni profile is quite successfully maintained in Mack’s new MP7 engine.

I was recently invited to test drive a 2006 Mack MP7 engine, and I will attest that this new engine still has that legendary Mack grunt in the low end of the power band, as well as very smooth transition from torque to horsepower when upshifting. And when climbing a hill, the lower the rpm went, the harder it pulled. Does that or does that not sound like a Mack?

Having not yet driven MP7’s green counterpart, Volvo’s 10.8-litre D11, I can’t say how it feels, and therefore can’t compare the personalities. I’m comfortable telling you, though, that Mack has delivered an engine that Mack fans will feel right at home with.

Mack will launch its 12.8 L MP8 (415-485 hp, 1450-1700 lb ft) in time for 2007, followed sometime later, probably, by a 16-L MP10.

THE MOTOR

The MP7 is a “clean slate” design for Mack. It’s an entirely new engine. While the common elements shared by Mack and Volvo (as above) provide tremendous synergy and savings in design, testing, and manufacturing costs, key unique features, like Mack’s V-MAC IV electronic engine controls, differentiate the products.

And being a new engine, it comes with none of the baggage customers might be concerned about, such as coolant burping back out of the surge tank-and of course, the failing turbocharger vanes.

“If anything,” notes Dave McKenna, Mack’s powertrain products marketing manager, “we were oversensitive to these and other concerns. If I were a Mack customer, I’d be watching the new product pretty closely too. Having said that, I can tell you we’ve literally changed the entire design, so a recurrence of the old problems isn’t physically possible.”

The coolant issues, for example, were more of a plumbing problem associated with the Vision chassis than the ASET engine, McKenna says. But that’s been taken care of, too, thanks in large part to the company’s new Advantage highway chassis.

Mack’s Pinnacle cab is pretty roomy

You’ll see a fresh new cooling package from Mack as it moves into 2007. Pinnacle models will incorporate a 1,380 sq-in radiator with new engine-mounted shrouds and fan rings designed for maximum efficiency. A 32-in fan will be standard, with a choice of three fan clutches: on/off; E-Viscous, electronically modulated; or a heavy-duty multi-speed fan that can be locked on.

Look for a new rad-mounted expansion tank, new coolant piping, new charge-air-cooler piping, new air intake piping, new power steering coolers, and a new cross-flow charge-air-cooler. While the ’07 hood profile hasn’t changed, under-hood airflow has been optimized for better circulation. A new bumper features a cut out for better airflow across the bottom of the rad.

“We’ve also gone with a stepped-vane variable geometry [Holset] turbo — entirely different from the old one — knowing that design would provide extraordinary life, as well as improved engine brake performance,” McKenna adds.

POWER PROFILES

Mack has maintained its three power profiles — or performance options with the MP series engines. The Econodyne version (1,200 rpm-to-1,800 rpm) is ideal for typical interstate and less-than-full engine-load applications where fuel economy is a priority; MaxiCruise (1,200 rpm-to-1,950 rpm) provides performance that’s needed for rolling interstate and full engine-load applications; while the Maxidyne (1,200 rpmt-to-2,100 rpm) provides the power for high-performance, severe-duty service typically associated with off-road applications.

The engine I drove was configured with the Econodyne profile, which McKenna admits isn’t the engine he’d recommend for that particular application. “But if it performs well there,” he says, “we’re doing something right.” The Maxicruise profile would have been a better choice, given its even broader power band. But that’s not to take anything away from the Econodyne’s performance — it did a splendid job in a tough environment.

The 10.8-L MP7 is in the same league as Cummins’ ISM, but it’s a notch smaller than Cat’s C13 (12.5 L) and the MBE4000 (12.8 L). Torque-wise, its 1560-lb ft rating stands it 190 lb ft lighter than the Cat, and only 90 lb ft lighter than the MBE4000. For a medium-displacement engine, it’s a powerhouse, especially when you consider the highly misunderstood value of torque.

Torque really is king these days. Horsepower is just another word for high fuel consumption. The 1,560-ft lb MP7 did a fine job on the two-lane Appalachian trails where I drove it, and I believe — geared properly — will do an equal or better job out on the Interstate.

THE MOUNTAINS

The truck came courtesy of Burns Motor Freight, a relatively small general commodities carrier based in out-of-the-way Marlinton, WV. They agreed to let me drive as I wanted on a regular day’s work for the truck. We moved two loads of wood chips at about 77,000 lb, and an 82,400-lb load of sawdust from various sawmills in the area to a paper mill in Covington, Va.
Those familiar with the area — northeast of Beckley, WV/north of Roanoke, Va.-will be aware that it’s all narrow, twisty two-lane road with barely 500 consecutive meters of straight-and-level pavement to be found anywhere. The Appalachian Mountains provided dozens of 8 to 12-percent grades, and more hairpin turns than an old James Bond movie.

Mike Miller, the truck’s regular driver, has worked for Burns doing more or less the same job for more than 25 years. He’s as smooth and competent as drivers come, and earned my approval as one of the best drivers I’ve ever run with.

He loves the MP7, noting that it pulls better than the 427-hp Mack ASET AC engine he used to drive (MP7 out-performs the ASET by a significant margin: compare ASET’s 1,460 peak torque at 1,300 rpm to MP7’s 1,560 peak torque at 1,100 rpm). He says the MP7 is quieter, easier to shift, and burns five gallons less fuel on the same run as the larger-displacement 427.

From the driver’s seat, that means more pulling power across a broader rpm range. Countless times, we’d rounded a tight little turn and just started climbing. With no room to take a run at a hill, all you can do is stuff your foot into it and let it pull.

Over the course of the day, we turned 452 miles, and I’d say that engine was running at or close to peak torque 75 percent of the time — at a very reasonable 180-205 degrees F — except when coming down the hills. And that’s where Mack’s new PowerLeash engine brake shone.

Despite the relatively small 10.8 L displacement, PowerLeash still manages 400 retarding hp at 2,100 rpm. The fan was programmed to cut in as well, upping retarding capacity by about 50 hp.

Had I known what I was in for that day in terms of driving environment, and before driving the MP7, I might have thought the 395-hp engine was under-spec’d for the application. And I’m sure there will be others thinking along the same lines. It’s a testament to the wonders of electronics and the Holset variable geometry turbocharger that an 11-liter engine can very effectively manage 80,000-lb loads on eight percent grades. This smallish motor is up to more than you might want to throw at it.

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