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Tractor Engines Gain More Horsepower

AS PRODUCTIVITY in agriculture continues to climb, so does the demand for horsepower. But instead of going to larger engines to get more power, machinery makers are looking at how to make their current size engines more efficient.

They are playing with horsepower and packaging to find ways to get more power out of the same engine or chassis size. In engineering terms, they are increasing power density or the “power per unit of volume.”

“We're increasing the power within a chassis size,” says Jason Hoult, product manager for AGCO Corporation. “The same size tractor is going up in power to make it more efficient and productive. Farmers used to do that for years — buy a tractor, then turn the screw on the pump to get more horsepower from it. With modern electronic engines, we can efficiently deliver this same benefit from the factory.”

Density vs. displacement

So why the focus on power density as opposed to increasing engine size? Three reasons. It's easier. It's cheaper. And from a sizing standpoint, it's just more practical.

AGCO's Hoult says Tier 4 emissions standards are adding a significant cost to the price of tractors. The easiest way to add value to offset these additional costs to the consumer is to add more horsepower to the tractor.

“Farmers know the costs are going up because of emissions, and that is what's driving tractors to go higher horsepower in the same chassis,” Hoult says. “By taking a midsize row-crop tractor and putting 180 to 200 hp in it, we are making it a very useful and usable tractor. It helps us justify the cost.”

In addition, since horsepower is a function of mass, a larger engine would require a larger tractor. But a larger tractor size may not be practical for existing infrastructures.

“We've reached a point where the efficiency for size is starting to fall off,” Hoult says. “To put power to the ground you need 100 to 110 lbs./hp. Tractors need to be so much bigger physically and implements need to be so much bigger to use the power on the top end. But they still need to fit on our roads and bridges.

“Already we have the world's largest production tractor at 630 peak hp and we are finding implements that large are not feasible in most areas of the country,” Hoult continues. “As tractors grow, implements must be designed to fully utilize this much power, which is difficult.

“And the emission regulations make it tough,” Hoult adds. He says the bigger the engine, the harder it is to control its emissions on a mobile platform.

Mitch Kaiser, Case IH Steiger tractor marketing manager, says the company is providing more efficiency out of the same size engine. “What we are trying to do on our end is to stay within a given size engine to make it more efficient, burn less fuel, but give it the characteristics of high torque rise and also better load characteristics,” he says.

Methods to maximize

For these reasons, rather than increasing engine size (or displacement), manufacturers are researching ways to tweak their existing engines to get more power. AGCO, for example, increased the PTO horsepower by 35 with the introduction of its Massey Ferguson 8600 and Challenger MT600C tractors. At the same time it set a new world record in fuel efficiency by breaking the 20 hp-hr./gal. barrier, beating the previous record by more than 4%.

Deere achieved a similar power increase in its 8000 and 9000 series tractors. “For example, our top engine horsepower before in the 8030 series was 330 engine hp,” says Matt Arnold, senior marketing representative for John Deere Waterloo Tractor Marketing. “Now we are up to 345. We've increased it 15 hp over our previous model within the engine envelope itself, within that 9-liter displacement. And at the same time we were able to maintain or maximize fuel economy.”

He says the company was able to achieve that performance increase by leveraging existing engine technologies borrowed from other industries like trucking. These technologies include cooled exhaust gas recirculation, variable geometry turbochargers, high-pressure common rail fuel system, and engine controllers.

“Turbochargers have really evolved,” Arnold says. “While some manufacturers have stuck with the old waste gate turbo, we've gone to a variable geometry turbo in certain models to virtually eliminate turbo lag.” With this technology, engine controllers can sense the load, determine what is needed and then adjust the pitch of the veins for more boost to match the load on the engine.

Case IH recently ramped up its 12.9-liter tractor engine 10 to 15 hp. It also added a feature called the Diesel Saver Automatic Productivity Management system to make the engine work with the transmission for added efficiency. “It's much like cruise control in a car,” Kaiser says. “Drivers push a button and instead of field speed, the feature will automatically put the engine in the most economical mode to cover the most acres using the least amount of power.”

What's the limit?

At the Nebraska Tractor Test Lab on the University of Nebraska campus in Lincoln, engineers recently finished testing a 585 (635 peak) hp Challenger MT875 to verify manufacturer performance claims.

“It's fair to say horsepower is increasing,” says lab director Roger Hoy. At the lab is the first tractor ever tested there — a Waterloo Boy, rated at 25 hp.

Lab assistant Andrew Schumacher says horsepower has been increasing at a rate of 3% a year since 1950 (see chart). “Over the first 25 years, the average horsepower is fairly continuous,” Schumacher says. “But that mainly has to do with companies competing with the use of horses and trying to prove the efficiency of tractors. Around 1950 you start to see a defined increase, which still continues today.”

So just how much bigger can farm machinery get? Hoy says 4-wd tractors are at or near the physical limits for both weight and size for trucking. Further growth in size may require that tractors be shipped in pieces to be assembled on site or could warrant the need for escort vehicles, greatly increasing shipping costs.

AGCO's Jason Hoult predicts 700 peak hp will be a ceiling on horsepower for tractors. The largest engine in tractors is currently an 18 liter. Any increases beyond 10 to 15 hp would require a larger engine to maintain the performance we have today, Hoult says. “We would need to go to a 21- or 22-liter engine, and that is getting out of the realm of what you could drive around,” he says. “You'd be looking at a locomotive on wheels.”

T.C. Truesdell, marketing coordinator with Claas of America, says producers wanting to increase performance will continue to demand more power. As a result, he says, it is impossible to judge if there will be a maximum horsepower in combines, for example.

“Hybrid crops and evolving harvesting techniques [chopping corn heads] all demand more horsepower to get the job done,” Truesdell says. “As farming evolves, so will the machines to do the work.”

Role of hybrids

In order to arrive at more horsepower, manufacturers say we will likely see alternative forms of power. “With the costs skyrocketing for diesel engines to meet emission regulations, you will see alternatives,” says AGCO's Hoult. AGCO showed a prototype of an electric drive RoGator sprayer in January.

Other companies also have exhibited hybrid prototypes. These include John Deere's electric E model tractors and New Holland's T6000 series hydrogen-powered tractor.

Experts say diesel engines remain the most efficient, least-cost way to grow horsepower. As a result, alternative forms of power are not likely to replace the diesel engine but will be used in conjunction with engines to drive pumps, motors and fans on the machine.

“There are no hybrid tractors on the market,” says Case IH's Kaiser. “The efficiency isn't there yet.”

What is horsepower?

HORSEPOWER IS commonly perceived as a type of force, but it is actually a rate of doing work, according to Andrew Schumacher, lab assistant at the Nebraska Tractor Test Lab. It is arrived at through the following calculation:

horsepower = work/time = force × distance/time

To illustrate how much 1 hp is, Schumacher compares horsepower to manpower. He says manpower used to be the standard unit for power before horsepower and is the amount of power a typical man can exert over a certain time. It is figured to be 1/12 of 1 hp.

“For instance if you look at the highest-powered tractor that we have tested here at the Nebraska Tractor Test Lab, you could either say it has 585 hp or 7,020 manpower,” Schumacher says. “Said differently, one large tractor can do the same work that 7,020 men were required to do in former times.

“Today the price of these big machines may not seem very reasonable,” Schumacher adds. “But when you think about how many men you would have to pay to do the same amount of work, it might change your perspective.”

How much horsepower do you need?

AGRICULTURAL ECONOMIST William Edwards, Iowa State University, says sizing machinery is a lot like buying an insurance policy — how much coverage is enough? “I'm sure that after the very slow and late harvesting season we had in 2009, many producers will conclude that their harvesting, hauling and drying capacity is insufficient,” Edwards says. “Yet, is it really wise to gear up for an unusual year?”

To help farmers properly match tractor horsepower to machine size, Williams has devised a fact sheet that addresses the question of sizing machinery according to factors such as number of acres, crops grown and labor availability. For a copy of the publication, go to

Edwards says the horsepower needed to pull a certain implement depends on the width of the implement, the ground speed, draft requirement and soil condition. The general formula for estimating the required horsepower measured at the power takeoff is:

PTO hp = width (ft.) × speed (mph) × draft (lb./ft.) × soil factor/375

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