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  1. #1

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    Default a tractor question.

    it true that a tractor engine makes much greater use of its power than a car engine? We all know that a car engine only uses its a lot of horsepower when accelerating only. This means most of the time the power demand is way below the capacity of the engine for car. This is not true for a tractor right?

    Let's say a 150 HP car only uses that much HP when it's floored, but most of the time during cruising, it may only require less than 20 HP, which is way below 150HP.

    But what about a 50HP tractor? I think a tractor will make much better use of the power than a car.

    Right?

  2. #2
    Super Star Member
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    Default Re: a tractor question.

    Seems related to the load in both cases.

    So, you are thinking the tractor is 'loaded' more than a car?

  3. #3
    Super Member Bob_Skurka's Avatar
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    Default Re: a tractor question.

    <font color="red">
    it true that a tractor engine makes much greater use of its power than a car engine? </font>

    The engines generate the horsepower, but the transmissions USE the horsepower and apply it to the task at hand. The two machines are geared for totally different purposes. A tractor simply cannot accelerate like a car due to its gearing. A car, conversely, cannot apply the power to the ground the way a tractor can. To effectively compare the two, you'd need to find a car and a tractor that had equal HP and equal weight. The car would be geared totally differently and apply the power differently than the tractor.


  4. #4
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    Default Re: a tractor question.

    IMHO, a tractor is a more specific use vehicle than the average car. Cars have to do stop and go, creeping driving. They also have to do high speed, up hill, down hill, and slow and fast curvies. Therefore, I think you are correct that a tractor is more efficient in applying horsepower because it is doing so in a very limited range - slow, strong, and steady. That is what it does and that is about all it does (in terms of translating power to action).

    Kind of an interesting question, really...but I'm not sure I needed to get this into my brain. ("Honey, did you take out the trash?" - "Uh, no, I was thinking, uh, about, oh, never mind, I've gotta take out the trash") [img]/forums/images/graemlins/grin.gif[/img]

  5. #5
    Veteran Member
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    Default Re: a tractor question.

    The concept of hp is lost in rpm. The tractor is more likely to out torque an engine in a car with the same hp. Think of what you tractor would do if it's engine was able to turn 5-7000 rpm. Keeping the plow in the ground probably wouldn't be too bad, it would be keeping the soil in the same field that would be difficult.

  6. #6

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    Default Re: a tractor question.

    Bob Shurka pretty well has it. The tractor has a transmission and a different gearing that makes it pull and use HP differently than a car. Of course, a tractor is not using all it's rated HP either unless you have the RPM up to rated speed, but the gearing allows the tractor to use the HP/torque for pulling heavy weights where the gearing and transmission of the car would not allow that. The HP would be wasted in spinning tires on the car. John

  7. #7
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    Default Re: a tractor question.

    Yes, the tractor uses much more of its 'rated' horsepower than a car. A tractor rated at 45HP @ 2600 RPM may also be rated at 37 PTO HP @ 2400 engine RPM. When running a PTO implement, the tractor engine is intended to be run continuously at that 2400 RPM....so, yes it's using a much higher percentage of its 'rated' horsepower. If needed it could operate continuously at 2600RPM without durability issues; though PTO operation at this higher RPM would probably cause issues with the implement.

    But notice; the so-called redline is much lower than you commonly find in an auto. In the tractor, the 45HP is being delivered by a 2.2 liter engine 'redlined' at 2600RPM. A 2.2 liter auto engine will commonly deliver around 140HP at 6000 RPM; which is at or close to it's own redline. The auto engine could easily run continuously at 2600RPM, probably delivering around 50HP, without any wear or durability issues; but not at 6000RPM. However the additional power that's available above 2600 RPM in an auto is available for intermittant use during acceleration.

    Power that's available from a tractor engine tends to be used continuously. Therefore, to keep it in one piece (among other reasons) it's rated at a much lower RPM/HP and governed to operate at or below the rated RPM.

    Piston aircraft engines are handled in much the same fashion because on takeoff and climbout the engine must deliver full power continuously for an extended period. Once at cruise altitude, only a modest power reduction is made and the remainder of the flight is conducted at 65 to 75 percent of maximum rated power.
    Bob

  8. #8

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    Default Re: a tractor question.

    There is also the issue of torque. Remember HP is just torque X time.
    A diesel produces much more torque at 2600 rpm then the equal size gas engine. This is how they get fairly good HP ratings at low RPM. I have a VW TDI and it red lines at 4300 rpm, very high for a diesel, but max torque is at 1900. You can feel the engine nose over above about 3300. My F350 red lines at 3300 and pulls all the way.

  9. #9
    Super Member Henro's Avatar
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    Default Re: a tractor question.

    unclehan,

    I think they are the same.

    A tractor transporting itself quickly across a field is like a car running down the highway, it is using a lot less than its maximum HP available while moving relatively fast.

    A car with a trailer that is heavily loaded, that is climbing a steep mountain grade, having to shift down to make it up, is similar to a tractor plowing a field, geared down and grunting to get the work done.

    I think the root, unanswered question is:

    At what point does a car become a tractor?

    [img]/forums/images/graemlins/grin.gif[/img] [img]/forums/images/graemlins/grin.gif[/img] [img]/forums/images/graemlins/grin.gif[/img]

  10. #10

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    Default Re: a tractor question.

    </font><font color="blue" class="small">( unclehan,

    I think they are the same.

    A tractor transporting itself quickly across a field is like a car running down the highway, it is using a lot less than its maximum HP available while moving relatively fast.

    A car with a trailer that is heavily loaded, that is climbing a steep mountain grade, having to shift down to make it up, is similar to a tractor plowing a field, geared down and grunting to get the work done.
    )</font>

    But I don't think tractors spend most of its operating life transporting itself acrossing fields. I think most of its time it's under load, doing some kind of task. But a car spend the great majority of time cruising. Only rarely do car have to tow a trailer or go up a steep hill.

    So yes while they both will encounter the same operating environment, the frequency is completely opposite.

    So I guess my orginal question is whether tractor tend to use a higher PERCENTAGE of its rated HP than a car.

    Let's say a 200 HP car only uses 200 HP when it's floored, but most of the time during cruising, it may only require less than 20 HP, which is way below 200HP. Say, it uses 10 seconds to accelerate up to speed (uses 200HP), then it spend the next 10 minutes cruising (uses 20HP). This means most of the time the engine is merely using 20 HP out of its available 200 HP. That's only 10%.

    But what about a 50HP tractor? I think a tractor will make much better use of the power than a car. It could possibily using only 10% of its rated power (which is 5HP in this case) like a car. I think the percentage will be much higher.


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