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profi Tractor Test: Big and Mighty (2008)

August 25, 2008

The brawny MT865 is muscular and built to work

Challenger MT865
Data Sheet

The sheer size of the Challenger MT800 Series, launched with four models ranging from 340 hp to 500 hp, is impressive. The granddaddy of them all—the 500-hp MT865—stands more than 11.5' tall from the ground to the top of the cab. Access to the cab involves a bit of a climb—up seven steps and along a 22.9' catwalk that runs from the front to the back of the machine.

Under the hood, power for the test tractor was abundant thanks to a six-cylinder Caterpillar C16 engine, which boasts 15.8-liter piston displacement, four-valve technology, and a pump and nozzle injection system.

Since profi tested the MT865, it, along with the other tractors in the series, have received an engine upgrade. Power for the MT865B (notice the addition to the model name) now comes from a Tier 3, Caterpillar C18 ACERT engine. This engine uses 18.1-liter piston displacement, with a mechanical electric unit injector to opiti- mize fuel delivery. The B series gained a model, for a five model lineup ranging from 350 hp to 570 hp. Claimed PTO output at rated speed (2,100 rpm) is 425 hp with a gross engine output of 570 hp.

Back to the test tractor, the profi team was eager to verify the bold horsepower claims. However, the test station's PTO power kit couldn't handle this level of output.

On to plan B. In reality, only a limited number of customers choose the PTO option. With that in mind, the test team focused on what the MT865 is really about—lugging power. At rated speed, the test station's brake wagon recorded 380 drawbar hp of the tractor's claimed 500 engine hp; at maximum output, the same lugging power scaled to a notable 460 drawbar hp. (The Nebraska Tractor Test Lab tallied 444.1 PTO hp at rated speed and 523.6 PTO hp at 1,750 rpm.)

These drawbar results suggest AGCO's maximum engine rates are realistic and unexaggerated.

Translating these figures into useful power is key to the MT Series, hence, the reason for tracks, rather than wheels. The test tractor was outfitted with 27.5"-wide belts (9.8' runs along the ground). The result is a more-than-25-ton machine with massive output potential, minimal wheel slip and little power loss. All of this is achieved at a ground pressure of slightly more than 7.1 psi.

At 2,100 rpm rated speed, the MT865's specific fuel consumption at 0.472 lb./hp/hr drawbar power was on par with high-horsepower wheeled tractors. However, the more important parameter is fuel consumption at 1,700 rpm, the engine revolutions per minute at which the MT865 produces its maximum drawbar power. Here, consumption drops significantly to 0.411 lb./hp/hr, which suggests that there is little point in running this tractor at full throttle; not only does the operator go through more fuel, but he or she looses up to 80.5 hp of engine power, too.

To describe the MT865 as economical would be a little far-fetched; at maximum output, the engine drinks 26.4 gal. of diesel per hour from its 330-gal. tank. However, the tractor proved itself capable of accomplishing much in an hour.

The tractor's transmission offers a somewhat limited choice of 16F/4R speeds, which translates into a minimal seven gears in the primary 2.5 mph to 7.5 mph working band. This isn't a significant problem, though, because the gears are evenly spread, which allows the operator to comfortably work within the most economical 1,700 rev to 1,800 rev band, a task further simplified by the option of tapping into three auto modes:

Maximum output mode: The transmission automatically shifts to the gear that allows the engine to rev for maximum output. When the MT865 faces sticky soil, it downshifts; once through the conditions, it shifts up. The operator can program the highest gear to be selected automatically, so in easygoing conditions, the MT865 doesn't build up surplus speed. In summary, the electronic system automatically keeps engine speed between 1,500 rpm and 2,000 rpm.

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FEATURED IN: Farm Journal - December 2008

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