What RPM?

[weiser]

At what RPM do you typically operate your tractor? I know this varies according to task, but - when you need the power - where do you like to set it? Isn't 2150 the proper engine speed for a 540 PTO attachment??

Does anyone here often operate their machine at or near the 2600 or 2700 RPM speed ratings that are listed in typical performance specifications tables? - That seems pretty high to me...

Does anyone here know where we can get torque and power curves for these machines?

 

[Bob_Skurka]

Certainly it depends on what I am doing, but for mowing, tilling, etc I run at/near full RPMs. For loader work, I run a little slower, just to reduce the engine noise, probably closer to 2200 rpms. The little engines are designed to run at their rated speeds. You get lower performance when you run at lower speeds. Loaders and 3pts will lose capacity if you don't run at a high enough engine speed to properly pressure your hydraulics.

 

[Bob_Young]

Yep, everything's more efficient at 540 PTO RPM. Don't wanna lose none o' that efficiency, no sir. Everbody knows that.

Even rocks. They can sure do an efficient job of trashing your mower blades at 540 or banging heck out of your tiller. Hidden iron pipes and old fence posts know it. So do old stumps hidden in the grass and that overgrown coil of barbed wire and that log chain that fell off the wagon last year. Yep, the results are in. 540 PTO RPM is the absolute best.

But I've never been willing to push MY equipment that hard. When running PTO driven equipment, I'm typically anywhere from 10 to 25% below 540. On a tractor that delivers 540 @ 2600 engine RPM, that's anywhere from 1950 to 2350 RPM. I pick the lowest RPM that gets the job done without causing the engine or drive train to labor. You develop an ear for it. It just sounds like its running easy. And your mind will run easier too; knowing that those blade tips and tines are traveling at 10 to 25% below rated speed....and packing anywhere from 81% to 56% of the rated kinetic energy when they smack something you didn't know about.

Of course this is the old farmer's approach to setting RPM, cuz way back when, the old Johnny Poppers and Farmalls didn't have tachometers.

But if you're mowing, tilling or whatever in an area that has absolutely NO surprises, then have at it. Let 'er rip. You'll get the efficiency you paid for with no additional costs.

Same thing for loader work. When running at rated RPM, the loader can react scary fast due to the high flow rate of the hydraulic pump. When I'm in a tight area or maybe not so sure of what I'm doing, I throttle waaay back...sometimes right back to idle. I don't want or need the sudden moves. I'd rather have a little time to analyze the results of my inputs before continuing. I'd also rather not do $200 worth of damage trying to do $50 worth of good.

But if you know exactly what you're doing and how your machine and your load will react, then run at rated RPM. You might finish your work a few minutes earlier.

People on this site obsess about the ROPS and the seatbelt...THINGS THAT WOULD NEVER BE NEEDED...if they slowed down a bit and were careful to avoid getting into trouble to begin with.

The Throttle is a safety device too. There are an infinite number of RPM settings between idle and rated. You paid for them. Pick the one most appropriate for the work at hand and live long and prosper.
FWIW
Bob

 

[herringchoker]

Using the PTO for the snowblower or bushcutter, I run my B7800 where it gives 540 RPM at the PTO, which is about 2600 RPM. Like Bob, for loader work I run the engine at about 2100 to 2200 RPM. ( I don't really know why, maybe I just got used to lower RPM's on bigger engines over the years...hard to teach an old dog new tricks )

 

[Glowplug]

When I'm mowing with my rotary cutter I run it at an engine speed that allows the PTO to turn at 540 RPMs which is about 2200 RPMs. For loader work I like 1500. Not a lot of noise but usually gives enough speed and power to get the job done. If I'm doing some delicate tight maneuvering (ie, trying to avoid tearing something up) I usually throttle down to about 1,000 RPMs. I have NEVER run it at wide-open throttle.

I'm not sure where you can find the torque and horsepower curves. But often the peak torque is at a low RPM like 1,000 and peak horsepower is somewhere around the rated RPMs.

 

[Nickahawk]

Wow! Great responces! I've ran ole Green machines (gas) for years. My Kubota L4400 is the first diesel tractor I've owned. I'm often concerned that I'm running RPM's too high or too low with it. I've always ran tractor RPM's at what seemed most practical for the job, by hearing the "sounds", by listoning to the engine and equipment being operated. If it sounded like everything was in "harmony" then that was cool! With the diesel I'm not sure if I should run it by the book or by sound! Also, i'm not sure if I should let it idle for 10 - 20 minutes if I'm not using it or shut it off. With the gas engines I would let them run for several minutes. What is best for diesel engines? I need expert advise!

 

[art]

Most engines sweet spot is around three quarters throttle gas or diesel. That is where the fuel consumpution to power produced is optimum for performance is achieved.

To run them at full throttle will produce more power but at a rate of high fuel consumption for the return. Diesels need to be keep warm or at operating temp more then anyting as to the way they run. The engine will not burn all the fuel when run cool so it is a matter of overall temps as to being better to let idle but normall five minutes is all that would be advisable.

 

[montelatici]

All the numbers are ok for most tractors, but the BX series produce full power at an unusually high RPM for a diesel. After coming from a Kubota B series the high RPM rating of the BX is a little annoying, but I guess I will get used to it.

 

[jimntex]

So what would the be the best RPM range to operate the BX in while operating the loader or backhoe?

 

[Jdengr]

Set your RPM so that you are comfortable with the SPEED at which your backhoe/loader operates.
In hydraulic systems, force is proportional to system Pressure and speed is proportional to flow. Your system pressure is NOT affected by RPM, only the relief valve setting controls that. The hydraulic pump takes a small fraction of the engines HP to run. These small tractors have an open center hydraulic system with a constant displacement pump. Every reveloution of the pump moves a fixed volume of fluid. Pumps do not make pressure, they make flow. Restrictions or loads make pressure. At idle you can bottom/top a cylinder out, forcing ALL hydraulic flow through the relief valve and the engine RPM won't slow much if any. Try it. With the engine at idle, dump your loader bucket and hold the contol in the dump position after the bucket stops. If you have a guage in the system it will read (or very close to 'cause of internal leakage) the relief valve setting. You may not even hear the sound of the fluid as it goes through the relief valve. Do the same thing with high engine RPM and the hissing/squeeling sound is the higher amount of flow through the relief, but a guage would show the same pressure as before.
PTO work is a different story. As the replies above state, run enough RPM to produce the power/speed to do the job.

 

[weiser]

great info there - thanks to all!!

Here's my reason for asking: I am looking at buying my first tractor, and - as I read up on the specs and judge cost with performance - I see the HP rating step up (around 5HP per model iteration) and (of course) cost steps up also. Often, other features or ratings step up as well, but sometimes not.

RPM rating also changes from model to model - giving me the impression that that this is a marketing strategy to design and market clear levels of increasing cost and value. Not to sound cynical here - that's just the way capitalism works.

But - what is the difference between 2600 and 2700 RPM? (I know: 100 RPM, you say!) But how often will I operate at 2600 or 2700 RPM? If the answer is "rarely," then the improved performance from 2600 to 2700 RPM is nearly meaningless...

Example: L4330 vs. L4630 - the 4630 is basically THE SAME TRACTOR, only rated to 2700 RPM. Because Horsepower is torque x RPM, the L4630 generates more Horsepower (at the 2700 RPM level). Why would I pay more for the L4630 - if everything else is the same, and IF I will rarely operate at or over 2600 RPM anyway?

I certainly don't mean to criticize those who manufacture the L4630, or those who have bought it. I am just trying to compare apples to apples...

 

[MadDogDriver]

But - what is the difference between 2600 and 2700 RPM? (I know: 100 RPM, you say!) But how often will I operate at 2600 or 2700 RPM? If the answer is "rarely," then the improved performance from 2600 to 2700 RPM is nearly meaningless...
I am just trying to compare apples to apples...

If you have a chance to look at torque perfomance vs. engine RPM data on diesel engines you'll notice that the torque will increase as RPM increases up to a point and will flat line beyond that RPM. Increasing your RPM beyond that point will not achieve any increased torque performance and just adds fatigue to the engine. Tractor manufacturers match that max torque engine RPM to achieve a 540 PTO RPM so you're getting max torque at 540 PTO RPM. Depending upon each individual engines specs that RPM will be different; 2475, 2600, 2700, 2200 etc. Granted that your HP will continue to increase with a higher RPM, but that does nothing for you in gaining performance out of your tractor. This has nothing to do with marketing, but simple engineering data, and not abusing your engine.

The previous posts are correct about setting your RPM at some nominal amount for the job you're doing. But if you need max torque, like when plowing or tilling for example, then you should set the RPM to the recommended 540 mark and not beyond it.

 

[rdsaustintx]

So what would the be the best RPM range to operate the BX in while operating the loader or backhoe?

All WOT, all the time.

 

[weiser]

Does anyone out there know the 540 PTO setting for the current Kubota models? Where can I get this? Even better would be the max torque value and the RPM at which that occurs.

Here are the models I am looking at:

L3400 Hydro

L3830 Hydro
L4330 Hydro
L4630 Hydro

L3940 Hydro
L4240 Hydro
L4740 Hydro

 

[Stackwood]

O.K., we've got an MX5000, which has a 50 hp, 4 cylinder diesel engine. As I recall one of the brochures on it showed the torque and power curves. Max torque was at about 1500 rpm. Max power was at about 3000 rpm. PTO speed is at about 2700 rpm, and it's plenty loud at that speed.

A few notes about engines:

You can do as much, or more, damage to an engine overloading it at low speed as you can overrevving it at high speed. I'm not sure it's possible to overrev these engines. Surely the valves aren't going to start floating at 3500 rpm, assuming it would rev that high! (never ran mine wide open). The head mechanic at our local dealership said that when Kubotas get brought in for a rebuild, it's due to low compression, causing them to not start. Everything else is solid. Makes sense to me. For longevity then, barring abuse, lower revs are better than higher revs for the same speed. Just don't bog down the engine.

One of the reasons diesels are more efficient than gas engines is that they have no throttle valve. That's right, they have access to all the air they can get all the time. Throttle settings are governed strictly by fuel input. Because of this a diesel can be more fuel efficient at low throttle settings than its gasoline counterpart. That said, it's my understanding that internal combustion engines are most efficient at maximum torque, assuming you're extracting maximum available power at that speed.

Here's how I run my tractor. At light loading, such as traveling to a destination, I run at low rpms, 1000-1500. I also run at low rpms for delicate loader work at low speeds, since I typically run out of traction long before I run out of power. These are approximations because I use the foot throttle a lot for both applications. For more demanding loader work, seeding, fertilizer spreading and the like, 1800 rpms is excellent on my tractor because it provides a nice buffer under load. If the load goes up and engine speed drops, my max available torque will actually be increasing. In other words, it's a sweet spot. For bush hogging, I run 2200-2500 rpms. Better to gear down if the going gets tough. I very rarely run at PTO speed. I haven't done any real ground engagement yet, but I think I'd stick with 2200-2500 rpms and just gear down if it wasn't enough, though time will tell.