What RPM?

[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.