The combination of a sophisticated integral full-flow and bypass oil filter and the efficient combustion produced by the ACRS means maximum oil change intervals up to 50,000 miles for on-highway engines.
International impressed the market with the 2008 introduction of its 11- and 13-liter MaxxForce Big Bore engines, featuring common-rail injection and a compacted graphite iron block. In 2010, the truck and engine maker declared it would use advanced EGR, rather than SCR, to meet the low 0.2 grams/horsepower/hour NOx standard for 2010.
Part of the recipe is International’s ability to burn credits, killing NOx down to about 0.5 grams per horsepower-hour while further development work proceeds. The result, claims International, is an engine that delivers fuel economy that is at least as good as its 2008 version. The combination of a relatively small 12.4-liter block of CG iron, and a vehicle that has no SCR catalyst or DEF tank, also helps ensure maximum payloads.
International says that because CG Iron is incredibly strong, castings don’t have to be as heavy, reducing weight by 500 pounds.
An important part of the design is the common-rail injection system. The fuel pressure is generated by a crankshaft-driven pump in which output can be adjusted for the conditions. It feeds a large pipe called a “common-rail” that is connected to all six injectors. It can generate maximum injection pressures even at 1,000 rpm. The company keeps raising the pressure to improve the system’s performance as it develops the engine.
Another secret is the engine’s “redesigned, double combustion bowl, which combines with the higher fuel injection pressure to break the fuel up into a finer mist spread evenly inside the cylinder,” says Tim Shick, director of marketing and field support in International’s big bore engine business.
MaxxForce Big Bore
Horsepower: 410, 430, 475
Torque:1,450, 1,550, 1,700, plus 1,750 multitorque
Bore and stroke: 4.96 in. by 6.54 in.
Displacement: 12.4 liters
Lube Oil capacity: 42 quarts
These features combined with cracked cap technology in the connecting rod bearings allow the engine to develop peak torque all the way down to 1,000 rpm.
The engine’s air handling system combines twin series turbochargers with an inter-stage cooler that uses low temperature coolant to remove the heat created by the primary turbocharger. This “increases air density to maintain peak power as speeds increase,” the company says. Also, “the smaller, primary turbo responds quickly for immediate takeoff at low engine speeds, and the larger, secondary turbo provides peak power at higher speeds and on steep grades.”
The exhaust entering the intake system is cooled to a low temperature in the final stage of the EGR cooler using low temperature coolant. Twin EGR circuits take advantage of exhaust pulses to help recirculate the exhaust with a minimum of backpressure, too.
2010 revisions include a Spinner centrifugal oil filter that increases change intervals for vehicles getting 6.5 mpg from 25,000 to 40,000 miles.
The Mack MaxiDyne engine of 1965 offered an unusual, flat power curve. Says David McKenna, Mack’s director of powertrain sales and marketing, “This was achieved with a broad expanse of torque at the bottom end. Where torque tapered as rpm rose, horsepower picked up the slack.”
Mack’s modern on-highway MaxiCruise engine, the 13-liter MP8, resembles the Maxidyne, though the curves are slightly different. “Customers always look for that bottom-end grunt that Mack engines offer,” McKenna says. “We had to maintain that.”