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ROAD TEST: MACK'S MP7 ENGINE


Despite the MP7's small size, it's still got that Mack grunt.

Mack Trucks raised a few eyebrows last year when it announced that they were tapping into a "new family of Volvo Group engines" to meet the EPA 2007 regulations. The basic architecture of the engines 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.

I 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?

Honestly, the only difference I could tell in what one would expect from a Mack engine was the sound, and the fact that the revs drop considerably faster than one would expect when upshifting – a nuance that caught me off guard more than once on the drive.
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.

The Motor
Back in 1967, Mack's Walter May and Win Pelizzoni co-designed the Maxidyne constant-power profile, incorporating high torque at low rpm, and smooth transition to higher horsepower (relatively speaking: 237 hp, 860 lb ft at the time). That profile is successfully maintained in the MP7 by Mack's V-MAC IV electronic engine controls.
Mack's camshaft is integral to the way the engine works and feels – valve timing, etc, – making a huge contribution to the performance and personality of the engine.
And being a new engine, it comes with none of the baggage customers might be concerned about, such as coolant burping back through the rad cap and out of the surge tank, and of course the failing turbocharger vanes.

"If anything," notes Dave McKenna, Mack 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.

"We've gone with a stepped-vane variable geometry turbo – entirely different from the old one – knowing that design would provide extraordinary life, as well as improved engine brake performance."

The coolant issues 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.

In fact, you'll be seeing a fresh new cooling package from Mack as it moves into 2007. Pinnacle models will incorporate a 1,380 sq-in. rad 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.

There will be 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. As well, under-hood airflow has been optimized for better circulation.

Three Power Profiles
Mack has historically offered its engines in three power profiles, or performance options. Econodyne (1,200 rpm - 1,800 rpm) is ideal for typical interstate and less-than-full load applications where fuel economy is a priority; MaxiCruise (1,200 rpm - 1,950 rpm) provides performance that's needed for rolling interstate and full-load applications; and Maxidyne (1,200 rpm - 2,100 rpm) provides the power for high-performance, severe-duty conditions – especially off-road applications.

The engine I drove was configured with the Econodyne profile, which McKenna admits isn't the engine he'd recommend for the hills of West Virginia. "But if it performs well there," he says, "we're doing something right." The Maxicruise profile would have been a better choice for the application we drove in, given its even broader power band, but that's not to take anything away from the way the Econodyne performed. It did a splendid job.


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 participate in this particular test drive, allowing me to do as much driving as I wanted on a regular day's work for the truck. We moved two loads of wood chips at 77,000 lb, and a load of saw dust at a legal 82,400 lb, 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, flat pavement to be found anywhere. The Appalachian Mountains provided dozens of 8-12-percent grades, and more hairpin turns than you'd find in a James Bond movie. In short, it's a terrific place to test an engine, and a very exciting and challenging driving environment.

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. He says it's quieter, easier to shift, and burns five gallons less fuel on the same run as the larger displacement four-twenty-seven.
It's worth noting that throughout the day, there may have been three opportunities to hit a controlled 60 mph on flat ground, making the higher horsepower of the ASET engine more or less redundant. Hills need torque, and the smaller MP7 out-performed the ASET by a significant margin (ASET's 1,460 peak torque at 1,300 rpm vs MP7's 1,560 peak torque at 1,100 rpm).

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

To its credit, the MP7 managed most of the hills 6th-over or 7th-direct through the Maxitorque ES T313 13-speed. Often, acceleration was possible in the climb, but an upshift wasn't, which tells me the engine is well suited to the terrain it was working in.
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. We were on the brakes a lot that day, but mostly with light applications.
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.
Torque really is king these days. Horsepower is just another word for high fuel consumption, so forget it. The 1,560-ft lb MP7 did a fine job in the Appalachians and I believe, geared properly, will do an equal if not better job out on the Interstate. Don't let the small package fool you.

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Mack MP7 engine Powerleash Econodyne Maxidyne Maxicruise