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HP ratings diffference

zipper Join Date: Mar 2006 Posts: 3 Canada

2003-02-28          50261

Is the 20 HP range engines in the garden series tractor the same one as in the 4000. My dealer told me that the engines are rated differently by the factory. I was asking him about why a used 455 garden tractor was rated the same horsepower as a used 4100. Are the engines different? I know they both are Yanmars.

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HP ratings diffference

Peters Join Date: Feb 2002 Posts: 3034 Northern AL   Pics

2003-02-28          50271

It depends if it is gross HP or at the wheels, but I would suspect that they are the same engine. The 4100 series is a 3 cylinder 61 cu in engine. The difference is the gearing and tractor mass. ....

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HP ratings diffference

johnson445 Join Date: Jul 2003 Posts: 19 mn

2003-02-28          50279

I believe the HP ratings are the same but at different RPM's. The 455 has the same HP but lower torque at a higher RPM than the 4100. Typically slower running higher torque diesel engines are more durable and longer lasting. I believe the 4100 is rated at about 2200rpms while the 455 is at 3200rpms. ....

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HP ratings diffference

TomG Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley

2003-03-01          50295

That's some interesting information. Higher rpm designs usually are used to get more work from smaller displacement engines. I think of HP as a measure of work and torque as a measure of force.

I'm not sure why the same engine would be tuned for a higher rpm (and presumably broader power curve) for a garden tractor. Maybe somebody has some ideas. One possibility is that the design produces more stable operation for what might be thought of as primarily a mowing machine. A broad power curve would mean the governor would be less active. However, a risk of the design is that if a load did lug the engine off it's peak torque, it could be more difficult to get the revs back.
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HP ratings diffference

Art White Join Date: Jan 2000 Posts: 6898 Waterville New York   Pics

2003-03-01          50299

It's been a long time since I looked at the horsepower and torque charts of engines. They raise the RPM to get more horsepower and to broaden the torque band. Rather than build the pump so it holds to a high torque rating at a lower rpm they allow the RPM band to be wider to keep a more modest torque overall allowing the engine to work less over a wider band and not produce major stress from the high torque load. ....

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HP ratings diffference

DRankin Join Date: Jan 2000 Posts: 5116 Northern Nevada   Pics

2003-03-02          50359

I don't have the numbers in front of me for the 400 series tractors, but the ones I remember get their max HP ratings at 3200 RPM's. The 4100 max's out about 2650. ....

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