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 | RRagent
Join Date: Oct 2005 Posts: 56 North carolina 
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2005-11-28 119999
Just purchased a New Kobota, What is the ideal RPM range to operate in until it gets 50 hours on it. I don't want to damage the engine by over reving,
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 | Art White
Join Date: Jan 2000 Posts: 6898 Waterville New York 
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2005-11-28 120001
The most important thing is to get it warm or to operating temperature before asking it to perform any high torque or load situations. It is wise to vary the engine RPM during this time and you will see that the most performance is delivered about the 2/3 to 3/4 throttle mark. ....
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 | beagle
Join Date: Jan 2004 Posts: 1333 Michigan 
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2005-11-29 120078
You can get the performance curve for your engine from the Kubotaengine website. Look in the owners manual for the engine model number, and you can find the performance curve on the site.
You will see that the engine will torque out at about 70% of rated HP rpm, and then begin to fall off. You will loose about 10% of available engine torque at higher rpms. This is a clear indication that you are operating the engine at a lower efficiency. As Art mentioned, vary the rpm's during break-in, but for most uses, there really isn't any reason to go beyond 2100 rpm. If you are running a finish mower, sometimes higher rpms will give you a better cut. I never run our machine over 2100 rpm, even when doing mower work. We just go a little slower.
Horsepower has nothing to do with how much "work" an engine can do, only how fast it gets it done. ....
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| RRagent
Join Date: Oct 2005 Posts: 56 North carolina
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2005-11-29 120081
Thanks, I appreciate the information. ....
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 | Chief
Join Date: Jul 2003 Posts: 4297 Southwest MiddleTennessee
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2005-11-29 120088
When it comes to operating pto driven implements; I strongly recommend following the implement and tractor manufacturer's instructions and recommendations of operating the implement at full pto rpm. The exception being for PHD's, generators, hay balers, and other implements that require a lower pto rpm to function properly. Most mowers will not cut properly if operated below the 540 or 1,000 rpm called for. They will cut but not as well as at full pto rpm. For other non-pto tasks, I agree and use only the rpm needed to complete the task which is normally between 1,800 to 2,100 rpm. ....
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| Tim
Join Date: Posts: 1
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2006-01-22 123216
Beagle
With all do respect to you.
To quote your statement.
“Horsepower has nothing to do with how much "work" an engine can do, only how fast it gets it done.”
Your statement is a contradiction in terms.
That is precisely what Horsepower is. Horsepower is the work done in a given time. According to James Watt 550 ft-lb./sec. or 33000 ft-lb./min. = 1HP.
Respectfully
Tim
....
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 | Peters
Join Date: Feb 2002 Posts: 3034 Northern AL
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2006-01-22 123222
Agreed. Work over time is HP. There is a long discussion of this somewhere in the posts. Usable HP for a tractor relates to more to the Torque as the tractor is not shifting gears. In general you are running for example down the fence line with the mower and hit a patch of lush thick grass. With a standard tractor you can not easily shift with out stopping. You hear the motor load down. With a low reving engine with massive torque, you add a little fuel. The engine speeds up slightly and adds torque. Conversely with a high reving engine with the same HP you can add fuel but you will not necessarily increase power as you are beyond the torque maximum. You will need to stop and shift to another gear.
Naturally with a Hydrostat this changes as you can easily slow down a little to compensate for the increase in load. ....
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| beagle
Join Date: Jan 2004 Posts: 1333 Michigan
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2006-01-22 123226
Work is not Horsepower ( or Power). Horsepower is how fast "Work" gets done. If you look at the units of the 2 terms, "Power" by definition is how long it takes to accomplish the same amount of "Work". What the units of the 2 terms say is that a 5hp engine can do the same work as a 10 hp engine, but will take twice as long to get it done. In other words, a 2hp engine can move 550lbs 1 foot in half the time as a 1hp engine.
Terms:
Work=Mass x Length
Power=Mass x Length / Time
These terms are used universally in Static Mechanics and Physics. The exact relationship between the 2 engines gets more complicated since the actual Power formulas have to account for losses and efficiencies. But this is how work and power are defined and calculated.
The true measure of what work an engine can do is the torque output.
Tim, look at the formula you wrote in your post. It says the same thing as this post. Not sure what the difference is. ....
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| BrendonN
Join Date: May 2004 Posts: 89 Central Kansas
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2006-01-22 123236
Seems like this topic causes a lot of confusion. One of the problems with talking about torque as the measurement of an engine's ability to do work it that torque can be increased or decreased through gearing whereas power cannot. Add a 2:1 dropbox on the engine and torque output will double, but you have not increased the engine's capabilities at all since the speed is halved. Total power available remains the same (minus a little for gear losses, of course).
As another example, take a 540 rpm PTO shaft delivering 25hp. To the implement, it makes no difference what the torque output of the engine is since the PTO shaft is delivering 243 lb-ft (calculated using the hp=(lb-ft)(rpm)/5252 equation). The engine might be a 1500 rpm torquer or a 3000 rpm revver, but torque, and thus power, available at the PTO shaft ends up being the same. For these reasons, engines are always rated by their power output, not torque. Look at the ID tag on an engine and it will list rated power but rarely will say anything about torque because by itself, torque does nothing. Lots of torque at zero rpm does no work at all.
The "torque rise" of an engine is also important in that if torque increases as speed drops, the power output can remain the same. This is where diesels shine as the torque peak is often well below the rated power speed and horsepower does not fall off as the speed drops. And, the diesel's peak power is often at a lower speed than a gasoline engine. Compare pickup engines and you will find that the gas engine's peak power is often at 4500 rpm or more. I don't usually rev my pickup to 4500 rpm so I rarely make full use of the gasoline engine's capabilities. Diesel pickups, on the other hand, make max power at around 3000 rpm. So, at normal engine speeds, the diesel is putting out far more power than the gas engine even if the gasser is rated for more peak power. ....
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