Tractor rpm's vs 540/750 pto

[cabinhollow]

First, I know if I do it wrong, I will destroy something. I do that all the time anyway, so no big deal. That is the reason I own a metal fabrication shop.
Have plenty of HP, so torque is no problem. 30-45 hp required equipment, 70+ hp tractor.
2100 rpm's = 540 pto
I should be able to put the pto in 750 and then run the tractor at 1500-1600 rpm's and have 540 pto output.
This will be for working in hay. I have 12 gears to play with, to get the right mph needed.
I have run the numbers 10 ways and they all = the 1500-1600 rpm range.
Less work for the engine, less fuel.
Is anyone doing this?

 

[ericm979]

(540/750)*2100=1512

The PTO transmission is after the PTO drive comes off the main shaft (on my current Branson and former Kubota), so the PTO gear won't affect ground speed.

If your tractor has DPF you may want to run it in the 540 pto gear anyhow for less soot accumulation.

 

[jenkinsph]

First, I know if I do it wrong, I will destroy something. I do that all the time anyway, so no big deal. That is the reason I own a metal fabrication shop.
Have plenty of HP, so torque is no problem. 30-45 hp required equipment, 70+ hp tractor.
2100 rpm's = 540 pto
I should be able to put the pto in 750 and then run the tractor at 1500-1600 rpm's and have 540 pto output.
This will be for working in hay. I have 12 gears to play with, to get the right mph needed.
I have run the numbers 10 ways and they all = the 1500-1600 rpm range.
Less work for the engine, less fuel.
Is anyone doing this?

Lots of tractors have this economy pto setting for reduced engine rpms. I say go for it if it does not bog down you should fine.

I use the 750 pto setting often on my tractor that is what it is for.

 

[CobyRupert]

How is this less work for the engine?
Work is work.

It's just less rpm's engine, but more torque-per revolution required.

 

[cabinhollow]

How is this less work for the engine?
Work is work.

It's just less rpm's engine, but more torque-per revolution required.

Less rpm's to do the job = less work/longer engine life/less fuel.
Same reason you have gears in you car/truck. Higher the gear, lower rpm's, less fuel need.
"As long as you have the hp/torque to do the job in that gear."
If I had a 45 hp tractor and did this, it would be more work for the engine, but I got 30-40 hp just setting there drinking fuel, not doing any work.
And on torque, while I have not seen the specs on this motor, the torque could be close to the same at 1600 and 2100 rpm's.

 

[CobyRupert]

So...
Consider: 2 trucks pulling a 10,000 lb load up the same hill, both are traveling at the same speed. - I think your saying the one in the higher gear does less work?
Nope, they BOTH pull 10,000 pounds up the same hill.
Just like your baler (say) going 2 mph (taking in x pounds of hay/second). The tractor is still providing the power required for a baler taking in x pounds of hay at 2 mph, no matter what the tractors engine rpms are.

Not sure what you mean by: "but I got 30-40 hp just setting there drinking fuel, not doing any work."

The truck in higher gear turns less rpms on it's crank (less wear) but is putting more torque into it's crank (more stress). Both trucks do the same work.

Now if you want to argue that the motors have different efficiencies at different rpms (i.e. what's the best spot on their rpm power curve) that's a whole other matter to be considered. Do you know that at 1500 rpm the motor is more efficient than at 2100 rpm?

 

[Deerherd]

I do it all the time to save fuel. Here is John Deere's explanation:

 

[ning]

The efficiency of an engine varies throughout its RPM range.

It's quite possible that an engine will require less fuel to do some amount of work at 1500rpm than at 2100rpm - obviously it's doing the same amount of work in both cases; it's just taking less fuel if it's being more efficient.

This is the idea behind cars with CVT transmissions - you run the engine where it's the most efficient for a given load, and you adjust the transmission to suit. In fact, it's the idea behind having a transmission, even geared ones. My motorcycle can do 60mph in first gear, but it's a **** of a lot more efficient to cruise in 5th or 6th gear at 60mph. Same amount of work done (at least, same amount of work put to the road - it's obviously generating a lot more engine and transmission friction along the way).

What the OP is doing is using the alternate PTO speed as a different gear; it's basically another transmission. The fact than many tractors consider 750/780/1080 rpm PTO speed as "econ" points directly at this. If you don't actually need the potentially higher power of 2100 (or whatever) RPM, use the lower speed range and save fuel.

My tractor's tach shows a range to use the "ECON" PTO setting, and another for using the normal 540 - the PTO will spin 540 in either case, if I've got the lever set right for the RPM range.

 

[cabinhollow]

Ran it today for 3+ hours, teddering hay.
PTO in 750, rpm's at 1650,
The gear that worked the best was just a little slow on ground speed.
About 1/4 less engine noise in the cab.
It was like cruise control on the road, just set and watch the wildlife.
This is SEKY hay ground, what we call level, most people call a big hill.
I'll see how it goes Fri with the sq hay baler.

 

[buickanddeere]

First, I know if I do it wrong, I will destroy something. I do that all the time anyway, so no big deal. That is the reason I own a metal fabrication shop.
Have plenty of HP, so torque is no problem. 30-45 hp required equipment, 70+ hp tractor.
2100 rpm's = 540 pto
I should be able to put the pto in 750 and then run the tractor at 1500-1600 rpm's and have 540 pto output.
This will be for working in hay. I have 12 gears to play with, to get the right mph needed.
I have run the numbers 10 ways and they all = the 1500-1600 rpm range.
Less work for the engine, less fuel.
Is anyone doing this?

Going to save thousands of dollars in fuel and tractor wear every day.