hp ? ... torque ... hmm

[Henro]

I think BeeX was the first to bring up the torque curve being different between gas and diesel engines. But I do not think he specifically addressed the rising torque curve of many diesel engines as compared to the falling torque curve of many gasoline engines.

Given the two engine types, if both were connected to identical gear trains doing identical work at rated PTO speed, and the load increased, with nothing else changing, they both would tend to slow down. BUT the characteristic of the diesel engine, that torque increases with RPM loss, wins out, as the load will end up causing less RPM drop on the system using the diesel engine, as compared to the gasoline engine.

For me, in practical terms this means that worst case the diesel may slow down and chug through the task at hand, where the gasoline engine may just slow down and stall out. Granted, in the VERY WORST case, BOTH would stall out. I have proven that time and again, when getting overly aggressive with my loader...

But in my mind, for tractor work, the diesel is the winner on average.

 

[Tornado]

So in your opinion, the 2501 hst has ~19 pto hp. Your saying a 4' rotary cutter would be the best bet?

Just wanted to clarify that the L2501 manual specifies that for rotary cutters, the max recommended cutting width is 60" and max weight for a rotary cutter is 770Lbs.

Ive seen people run light duty 6' cutters on the L2501 and it ran it fine. If you take it easy and use common sense. Personally id let 5' be my max on a mower with my L2501. That would put the mower and the same width as the rear tires and is just a better situation all around.

With that said, I will add, that while it doesnt require any PTO power, I regularly use a disc harrow that is over the recommended rating for the L2501. Disc Harrow max size recommendation for L2501 is 60", and 660 LBS. I pull a 76" 705LB harrow and have had no issues. In all but the worst of conditions I can pull it in 2wd with both front and rear tines in the 2nd to most aggressive setting. If I go to the absolute most aggressive settings, It will spin the tires in 2wd a lot - Going into 4wd alleviates that and I can pull it fine at most aggressive. I like to pull it in 2wd so stay in the slightly lesser aggressive setting. The point is, all of this stuff is situational and dependent on many variables. If youre just mowing bahia grass in a cow pasture you could pull a 6 foot cutter just fine on an L2501 and have no issue. Its all in what youre doing. I like to look at these tractors as having I call a soft cap rather than a hard cap on what a limit is. 5 foot rotary cutter would be my soft cap.

 

[beex]

I think BeeX was the first to bring up the torque curve being different between gas and diesel engines. But I do not think he specifically addressed the rising torque curve of many diesel engines as compared to the falling torque curve of many gasoline engines.

Given the two engine types, if both were connected to identical gear trains doing identical work at rated PTO speed, and the load increased, with nothing else changing, they both would tend to slow down. BUT the characteristic of the diesel engine, that torque increases with RPM loss, wins out, as the load will end up causing less RPM drop on the system using the diesel engine, as compared to the gasoline engine.

For me, in practical terms this means that worst case the diesel may slow down and chug through the task at hand, where the gasoline engine may just slow down and stall out. Granted, in the VERY WORST case, BOTH would stall out. I have proven that time and again, when getting overly aggressive with my loader...

But in my mind, for tractor work, the diesel is the winner on average.

Right I didn’t specifically say the torque curve rises as the rpms slow, but it all cases, even though the torque rises, as rpms drop, the combination of the 2 is a drop in power. But the drop in power of a ‘high torque low rpm motor’ is small compared a low torque high rpm. So it doesn’t stall.

Even within diesel you have that trade off as pointed out in the OP.

Also it’s a not really true that gas motors cannot be torquey, it’s just they are not typically designed to be as torquey because you’re giving up a lot of HP doing that. Gas gives you a lot more hp/displacement therefore more hp / $ than diesel, so that’s what they design them that way. But didn’t used to be that way.

For example an 1970 IH 140 gas tractor WOT was 1400 rpms, about 26 hp, very torquey. idle was about 500. There’s no diesel tractor today in that power range with that much torque to run at 1400 rpm pto speed. It was a 2L in-line 4. Small bore and very long stroke. compression ratio only 7:1, it would run on garbage.

At the same time you can get a 26 hp v twin Kawasaki that runs at 3600 rpms, about 750 cc, much cheaper and smaller motor, fits in a zero turn.

The 140 2L won’t cut grass any faster than the Kawasaki.


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[Dunbar]

My HST L2501 works much harder running my RCR1860 60" rotary cutter than it does running my FDR1672 72" finish mower. Of course I'm cutting pasture grass with the finish mower and emerging jungle with the rotary cutter. I was surprised looking at the owners manual specs that the rotary cutter weighs less that the finish mower. Even though it cuts a foot less in width it is a much beefier unit. It weighs in at 599lbs where the 72" finish mower is 619lbs.



For anyone considering a finish mower for their L2501 I would definitely get a 72" unit unless you are using it on really rough vegetation. I can really move running it. I have the optional floating top link on my QH15 and use my float valve on the Tilt of my TnT hydraulics so the unit really follows the contours well and rarely scalps going through swales and dips.


I am happy that I upgraded my rotary cutter from the RCR12xx series. The 1260 is 478lbs so over 120lbs lighter than the 1860 but more important than the extra armor, the 1860 has a slip clutch rather than a shear pin. I know I would have gone through a dozen shear pins by now cutting jungle and hitting short hidden stumps. Hogging is a violent task.

Just wanted to clarify that the L2501 manual specifies that for rotary cutters, the max recommended cutting width is 60" and max weight for a rotary cutter is 770Lbs.

Ive seen people run light duty 6' cutters on the L2501 and it ran it fine. If you take it easy and use common sense. Personally id let 5' be my max on a mower with my L2501. That would put the mower and the same width as the rear tires and is just a better situation all around.

With that said, I will add, that while it doesnt require any PTO power, I regularly use a disc harrow that is over the recommended rating for the L2501. Disc Harrow max size recommendation for L2501 is 60", and 660 LBS. I pull a 76" 705LB harrow and have had no issues. In all but the worst of conditions I can pull it in 2wd with both front and rear tines in the 2nd to most aggressive setting. If I go to the absolute most aggressive settings, It will spin the tires in 2wd a lot - Going into 4wd alleviates that and I can pull it fine at most aggressive. I like to pull it in 2wd so stay in the slightly lesser aggressive setting. The point is, all of this stuff is situational and dependent on many variables. If youre just mowing bahia grass in a cow pasture you could pull a 6 foot cutter just fine on an L2501 and have no issue. Its all in what youre doing. I like to look at these tractors as having I call a soft cap rather than a hard cap on what a limit is. 5 foot rotary cutter would be my soft cap.