Torque RPM?

[geneP]

I see some engines have a "Torque RPM" in the specifications, some don't. I'm thinking, and correct me if I'm wrong, that this the the RPM that the engine develops it's max torque. The things that are bugging me: (1) are you harming the engine to work it below the advertised torque RPM as long as it isn't lugging? (2) Does anyone know the torque RPM on the Kubota 5-cylinder 2.7 (F2803-DI) engine? I can't find it anywhere.

The reason I'm concerned is that as I get acquainted with my tractor I find I can usually accomplish most jobs with 1000-1400 rpm and the tractor handling it fine. I usually run the 5' brush cutter about 1700 engine RPM cutting grass. The tractor likes this and the cutter does a good job. If I try to run it around the ~2200 rpm for 540 attachments the engine sounds like it is screaming. I have a full belly pan and this might be contributing by throwing the noise back up to me.

Do you other 5-cylinder owners find the engine noisy? Thanks for your comments.

 

[mkreitler]

On 540 attachments you run the engine at the specified RPM for 540 PTO revolutions regardless of the sound of the engine the engine is designed for this and that is why the manufacture species a certain engine RPM for the 540 RPM of the attachment whatever it may be. As long as nothing on the governed speed of the engine in question has NOT been changed from factory settings everything should be good to go. With it being a 5 cylinder it may sound a bit different than say a 3 or 4 cylinder.

 

[jaotguy]

1 ... as long as you are not lugging the engine , you can run it below the Torque RPM all day ..... it is when you are pushing the unit and need maximum torque that you run it in that range .... (any faster and you are just flogging the engine for no reason )

if 1000 -1400 works well , use that speed , as long as it gives a good result (but maybe 1200-1400 would be a better range ) ... being water cooled , you don't have to keep the RPM up to keep the engine cool with more airflow.

 

[rbargeron]

Hi Gene -

Torque ratings are generally stated at a specified RPM. Same goes for horsepower -an RPM is stated with it. Not familiar with the term "Torque RPM" by itself The usual form is "Max Torque (@ rpm)"

Regarding the F2803, the attached screen shot from the brochure shows the engine curves, indicating a max torque around 155 ft-lb at about 1650 rpm. The torque curve is relatively flat and early-peaking, good in a tractor engine.

The curve is given for rpm between 1200 and 2450. Below 1200 the governor response is vague, and above 2450 there's nothing to be gained. 1200-2450 is normal operating territory.

My F2803's are noisy too but at 1700 it's not bad (I use noise-cancelling headphones from John Deere ).

I converted my pto gearboxes to have 2 speeds, 540 and 750 with engine at 2200, but it's only the snow blowers that benefit much. The finish mowers go plenty fast enough at 1700 engine rpm, running pto low at 420 or high at 540

 

[geneP]

Thanks Dick, that chart has interesting information on it. I've printed it to place in the operator's manual.

The engine horsepower is low at 1200-1400 RPM but, as you said, the torque curve is relatively flat and is high at those RPMs.

You mentioned your two-speed PTO: I have no need for a snow blower, but my Land Pride brush hog has a gearbox with a ratio of ~1:1.85 as calculated by rotating the input shaft and counting the blade rotation. Most gearboxes I see advertised have a ratio of 1:1.47. This calculates to about a 25% increase in rotating speed on my cutter, so I think my blades are spinning at about the normal cutter spec when my engine RPMs are around 1700. It is a 5' cutter, so this tractor pulls it fine in 5th gear at 1700. My tires are R4s, so my speed is a little less than R1s at a given RPM.

You always provide great information, and I appreciate it.
Gene

Edit: I just looked up the specs on the Land Pride 1860 and the gearbox ratio is 1:1.93

 

[rbargeron]

......my Land Pride brush hog has a gearbox with a ratio of ~1:1.85 as calculated by rotating the input shaft and counting the blade rotation.......... I just looked up the specs on the Land Pride 1860 and the gearbox ratio is 1:1.93

You say I offer good info - but YOUR casual observation is within a factor of 0.04 - not too shabby yourself there, Bud !

 

[dodge man]

Just my opinion here, but people worry to much about reving an engine. They feel if they keep the rpms down they are saving the engine. Don't be afraid to rev it up, it's designed for it. It's obviously not needed to have the throttle wide open for light loader work but I'd think something barely above 1000 rpms sounds pretty low.

 

[rScotty]

I see some engines have a "Torque RPM" in the specifications, some don't. I'm thinking, and correct me if I'm wrong, that this the the RPM that the engine develops it's max torque. The things that are bugging me: (1) are you harming the engine to work it below the advertised torque RPM as long as it isn't lugging? (2) Does anyone know the torque RPM on the Kubota 5-cylinder 2.7 (F2803-DI) engine? I can't find it anywhere.

The reason I'm concerned is that as I get acquainted with my tractor I find I can usually accomplish most jobs with 1000-1400 rpm and the tractor handling it fine. I usually run the 5' brush cutter about 1700 engine RPM cutting grass. The tractor likes this and the cutter does a good job. If I try to run it around the ~2200 rpm for 540 attachments the engine sounds like it is screaming. I have a full belly pan and this might be contributing by throwing the noise back up to me.

I think "Torque RPM" is simply a different way of saying "Horsepower". By definition, Horsepower is simply equal to Torque multiplied by RPM, so most probably "Torque RPM" is just a different word for Horsepower.

I've worked on and around engines and engine design for over 50 years as a shop owner, machinist, and mechanical engineer. Personally, I rarely run an engine at it's full rated horsepower unless it's for brief spurts or in competition. Yes, I agree that any modern engine is designed to be run at close to max speed without damage.....but that's just considering damage to the engine. What about the poor operator? And what about his enjoyment of the job? IMHO, those are much more important.

Now I don't like to lug an engine anymore than I want to run it wide open. But I do like to run it where both of us are most happy...and that means I'll typically set the hand throttle to run it just far enough above idle that the governor can pick up the power in time to avoid lugging down too much when the situation calls for more power. Matching the load to the torque by changing fuel flow and RPM is exactly what a governor is designed to do. And I like to listen to the governor doing it's job; it's musical. On the M59 and JD310 we set the hand throttle at what we call a "high idle"..... and that tends to be somewhere between 1000 and 1500 rpm depending on the implement and the job. That's where we run everything.

Working that way is less tiring for us everyone, and in half a century of being around literally hundreds of engines I've never seen or heard of an engine being damaged by being run at a reasonable speed.
good luck to you all,
rScotty

 

[rbargeron]

.....Horsepower is simply equal to Torque multiplied by RPM......

HP = Torque X RPM / 5252. see link. The diagram above shows the F2803 engine making 155 ft-lb at 1650 rpm or about 49 hp, plenty for many jobs.

 

[buickanddeere]

It's not an irrigation pump, prime power generator or a marine propulsion system. Two lifetimes of work will make an insignificant difference to a CUT's wear and fuel consumption . Operate at reduced rpms if you wish but as soon as lugging occurs, nothing is being gained and wear is being increased by operating at peak torque and peak combustion chamber pressure..

 

[rScotty]

HP = Torque X RPM / 5252. see link. The diagram above shows the F2803 engine making 155 ft-lb at 1650 rpm or about 49 hp, plenty for many jobs.

Yes, I'd say both are correct in their own context. You wrote your definition as a formula using mathematical notation. When using such formal notation it is quite correct to include constants.
My goal was a little different. I wanted to use a conversational format to show in an informal and non-mathematical way how even an obscure term like "torque RPM" can still contain the basic things we need to consider for calculating horsepower.
thank you,
rScotty

 

[Baby Grand]

One thing to avoid for good engine health is bogging down/stalling. The journal bearings hate to run at low speed & high torque conditions, due to a breakdown in the hydrodynamic film thickness. As the film thickness is reduced, metal to metal contact between the high spots starts to occur, causing increased heat and wear.

Looking at the characteristic curves supplied by rbargeron, maybe try running the engine at a higher speed than you have - say 1800 - 2000 RPM, even if you don't need the HP or torque. My reasoning is twofold:

First, as jaotguy noted, the water pump will be doing a better job getting the heat out of the engine and into the radiator. A well cooled engine is a happy engine.

Second, as rbargeron notes, the engine torque curve has a peak at the low end. This can be used by an operator to good advantage by taking note of engine speed in response to increasing load. As engine speed starts to drop off, torque increases and the engine can maintain the load. After the engine passes the point of max torque, though, increasing load will rapidly bog down the engine. Running well above the peak gives you time to react to increasing load and decreasing engine speed before the engine bogs down or stalls. Your journal bearings will thank you.