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International Truck and Engine's MaxxForce engines are ideal for severe-service vehicles. Photo: International Truck and Engine

The DD15 uses turbo-compounding for improved fuel economy and quick demand torque response. The technology uses an exhaust-driven turbine to capture waste heat from the exhaust and use it to boost power. Torque response is the time it takes for an engine to go from minimum to maximum torque. In 1.5 seconds, you can use full torque from the DD15, compared with only 35% from the old Series 60—which takes 4.4 seconds to reach maximum. Fuel economy is improved by 5% over comparable Series 60 engines.

QUIET, DURABLE ENGINE

International Truck and Engine Corp. launched the MaxxForce engines earlier this year. Both MaxxForce 11 (10.5 liters) and MaxxForce 13 (12.4 liters) are available in International WorkStar severe-service vehicles.

International developed the engines in conjunction with M.A.N. of Germany to meet current and future emissions standards. They're constructed of compacted graphite iron, which is 70% stronger and 40% stiffer than compacted grey iron competitive engines, with double the fatigue limit. The MaxxForce weighs only 2,244 pounds dry.

Power for the 11-liter model ranges from 330 hp to 390 hp with 1,250- to 1,400-foot-pounds torque. The larger engine produces 420 to 475 hp, with torque ratings from 1,450 to 1,700 foot-pounds.

Peak torque is steady from 1,000 to 1,200 rpm, with more than 90% available through most of the range. Although maximum power is at 1,900 rpm and vocational engines are rated to 2,100 rpm, the engine is most efficient at lower revolutions per minute.

I drove several variations on interstates and around a tight course similar to urban maneuvering. The engine is so quiet, it was difficult to shift by ear. Newer drivers will find it easier to adapt their driving style to the engine's characteristics than older ones like me who may have to unlearn old habits.

The engine is very forgiving. Several times, I missed shifts and managed to grab a gear at around 700 rpm. Each time the engine pulled slowly and steadily back into its torque range, getting me out of trouble without any shuddering or bucking. Of course, with an automated or an automatic transmission, that won't be a problem. For optimum performance and economy, operating at lower rpm is better.

— Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Association, a board member of Truck Writers of North America, and active in the Society of Automotive Engineers.