Show of force

International’s new heavy-duty – but less than heavy – engines prove their stuff with strong, quiet rides.

Competition is a wonderful thing. For truckers, two recent products that best exemplify this claim are the 11- and 13-liter MaxxForce engines from International Truck and Engine Corp., first announced two years ago and formally introduced in late January.

The big bore MaxxForce duo, with a combined horsepower span of 330 to 475, offers users impressive fuel economy, solid low-end pulling power, quiet operation and, as if that weren’t enough, an overall package that weighs much less that comparable engines. As rising fuel prices drive engine makers to achieve greater levels of fuel economy, products that weigh several hundred pounds less than their competitors, as do the MaxxForce engines, will have a clear edge.

MaxxForce engines are the results of an alliance between International and MAN Nutzfahrzeuge, headquartered in Munich, Germany, to collaborate on design and manufacturing of components and systems for commercial trucks.

The benefits of this collaboration were demonstrated two months ago when International summoned trade press members to the Las Vegas Motor Speedway for a drive test. I selected a 2008 ProStar powered by a MaxxForce 13, set at 430 hp and 1,550 lb.-ft. of torque, and geared through a 10-speed Eaton transmission. The tractor was hitched to a loaded flatbed, for a combined weight of 61,000 pounds.

The initial thing first-time drivers will notice about the MaxxForce engine is its sound, or lack thereof. I wasn’t packing a decibel meter, but I could tell the engine was noticeably muted. International officials warned test drivers that they probably wouldn’t be able to “shift by ear” because of the lack of audible cues. That wasn’t quite the case for me, but I did need to listen more carefully.

Several factors help quell the noise, says Dave Schaller, senior program manager for International. “The high-pressure Bosch common rail fuel system [capable of an eye-poppin’ 26,000 psi] is one of the reasons the engine is quiet,” he says. Full pressure and maximum torque occur at very low rpm so there’s no need to rev up just to achieve more power. Also, in on-highway applications, all of the front-end accessories are turned with a single belt. The fan is gear driven. Fans in severe-service trucks, however, are belted to help dampen shock loading during clutch engagement.

Our test route was a mere 23 miles and didn’t include much terrain diversity. We ran north from the speedway on I-15 to U.S. 93 North, then returned. The only real display of the MaxxForce’s much-touted low-end torque occurred during the short climb up an interstate ramp. Accelerating up this brief (roughly 7 percent) climb, I was grabbing gears in reasonably rapid succession, and each time I did the engine dipped to about 1,100 rpm, then spooled steadily higher until the next shift point. This engine is operating in a zone once dominated by the frighteningly low-lugging Mack Maxidyne.

The Bosch fuel system is an integral part of this capability, but so, too, are the engine’s dual turbochargers – one for the low end, the other for high – which provide full boost across the rpm spectrum. This combination should satisfy the power needs of most on-highway operators, excluding heavy haulers and others who really need a full 15 or 16 liters under the hood. Equally important, though, the turbo and common rail systems are delivering good fuel economy, according to a few of the fleet managers who’ve been testing the engine for International.

“We started running a MaxxForce 13 last April, and it’s averaged about a half-mile per gallon better than the other engines we have, ” says Larry Mead, service manager for Cliff Viessman Inc. in Marshall, Minn., a 400-truck food-grade tank operation headquartered in Gary, S.D. “At first, we had it set at full power [475 hp and 1,700 lb.-ft. of torque], but we later cut back to 410 hp and 1,450 lb.-ft. of torque, and that really bumped the mileage.”

International officials attribute much of the engine’s reduction in poundage to compacted graphite iron from which the block is cast. CG iron reportedly is much stronger yet lighter than other metal used in heavy industrial forging. MaxxForce is the only large diesel made from the material, although “nearly all of the NASCAR race teams use it,” says Steve Perkins, big bore specialist for International. There are other benefits, too. “Because of the structural strength of CG iron, we were able to build a rear PTO drive right into the block,” Perkins says. “That adds to operating efficiency.”

My only issue with the MaxxForce was its engine brake. I activated it at full power on my descent to Speedway Boulevard, but found its slowing assistance to be minimal.

Asked about the engine brake later, officials said it isn’t a standard compression-type device. Rather, it’s a hybrid system that starts with an exhaust butterfly, gradually building enough backpressure to override exhaust valves, yielding something akin to compression braking. These tandem forces should generate up to 300 braking horsepower. Perhaps the unit in my test truck simply needed some tuning.

The big bore MaxxForce just went into production, so some adjustment can be expected. If internal-brake performance is the only nettlesome issue, International could be on the cusp of a huge product success story.

MAXXFORCE 11
DISPLACEMENT: 10.5 liters (641 cu. in.)
BORE AND STROKE: 120 mm x 155 mm (4.72 in. x 6.10 in.)
COMPRESSION RATIO: 17:1
ASPIRATION: Twin-series turbocharger, air/coolant intercooled
COMBUSTION: Direct injection
COOLING SYSTEM CAPACITY: 49 liters (52 U.S. quarts) (engine only)
LUBRICATING SYSTEM CAPACITY: 42 liters (44.5 U.S. quarts)
TOTAL ENGINE WEIGHT (DRY): 2,244 lbs. (1,018 kg)
VALVES: 4 per cylinder, overhead cam actuated
TORQUE RANGE: 1,250-1,450 lb.-ft. @ 1,000-1,200 rpm
CLUTCH ENGAGEMENT TORQUE: 660-830 lb.-ft. @ 800 rpm

MAXXFORCE 13
DISPLACEMENT: 12.4 liters (757 cu. in.)
BORE AND STROKE: 126 mm x 166 mm (4.96 in. x 6.54 in.)
COMPRESSION RATIO: 17:1
ASPIRATION: Twin-series turbocharger, air/liquid intercooled
COMBUSTION: Direct injection
COOLING SYSTEM CAPACITY: 49 liters (52 U.S. quarts) (engine only)
LUBRICATING SYSTEM CAPACITY: 42 liters (44.5 U.S. quarts)
TOTAL ENGINE WEIGHT (DRY): 2,244 lbs (1,018 kg)
VALVES: 4 per cylinder, overhead cam actuated
TORQUE RANGE: 1,450-1,700 lb.-ft. @ 1,000-1,200 rpm
CLUTCH ENGAGEMENT TORQUE: 830-960 lb.-ft. @ 800 rpm

MaxxForce engines are available now for Class 7 and 8 International trucks.

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