Oil & Fuel Diesel lugging power vs RPM

simonmeridew · Jan 3, 2006

My question is more a theoretical question: I have a new(14 hours)Kubota L4400 gear drive, and also have an old(1951) Ford 8N (with a newly rebuilt engine), which I've owned for 28+ years.
The 8N, even though it's gasoline, not diesel, has tremendous low end (since the rebuild) lugging power and torque. I don't ever need to use it at a higher RPM than 1200 to 1250 RPM. I use it all summer to mow the lawn with a 5 foot pull behind mower. Red line is probably 2200 RPM.
Since I got the Kubota a couple of months ago, I was advised to operate at the 540 PTO RPM something in the neighborhood of 2600RPM, even when not using a PTO implement, like with the FEL. But for the uses I have right now, including using a heavy duty 3pth Farmi logging winch and front end loading work, even skidding out 2000+pounds of logs at a time, I find I have plenty of torque and speed/power at just above idle, which amounts to 1200-1300 RPM. Twice I almost stalled it out when I ran the loader into a pile of gravel too deep geared too high(I'm really new with a loader), but otherwise RPMs stay pretty well constant while working. Maybe my tractor is simply overpowered for the type of work I'm doing.
My question is: is there a difference in the type/amount of torque in some of the older gasoline/diesel engines like I've seen in for example old JD bulldozers and tractors like my 8N, compared to what is in my Kubota, where I am advised to use it at PTO speed? Is it a different kind of power? Does it have something to do with valve timing, bore and stroke with newer type engines? Do I need to keep the RPMs up even thought I don't need the power? Quite simply put I always thought diesel engines were supposed to lug way down and still have plenty of torque. (My Polaris 4 wheeler needs to scream in order to do any work, like 4-5000 RPM)
simonmeridew

GaryE · Jan 3, 2006

Do I need to keep the RPMs up even thought I don't need the power? 

In my opinion, no. I run my 3710 @ 2000 RPM or less for almost all of my work. With the only exception when using my RMM where I need to keep the blade speed up. I run my BH which has a PTO pump @ ~1800 RPM and pull my BB at about the same. FEL work is done @ ~ 1500 RPM unless I am in a hurry. Engine almost never lugs, if it does I just bump up the engine speed a couple hundred RPM. Never have any problems. I see no need to run at PTO speed unless you need to.

Hope this helps,

Gary

Toolguy · Jan 3, 2006

I don't think it is necessary to run any engine at WOT unless you are using the PTO and WOT is rated PTO speed. I would recommend that you run your engine at the minimum speed necessary to do the work without lugging the engine. Higher RPMs will make the hydraulics faster and allow the HST to work more efficiently. But, that does not mean you have to do that all the time, rather, only when needed. You will also save fuel and extend the life of the tractor as well.

Posterboy · Jan 4, 2006

My owner’s manual said among other things.
"Do not operate the Tractor at Full speed for the First 50 hours of operation".
"Do not run the engine at speeds faster than necessary".

My RPM’s top out at 2900 and PTO speed is at 2600 RPM.
Other than Transporting, I do not use full throttle.
Mowing, Bush-hogging and Shredding I will use PTO speed.
FEL work I run around 1600 to 2200 RPM depending on type of material and work being done. 1600 RPM works well flipping compost. If moving or spreading dirt or stone 2000 to 2200 gives plenty of power and speed to fill the bucket and move it to the target.

The amount of torque that an engine produces depends on many variables. Volume of cylinders, valve size and timing, fuel type and metering device, ignition source, compression ratio, supercharged or normally aspirated and many others.

Diesel engines can be lugged down more so than a gas engine and still have good torque. Diesel fuel burns slower than gas, this is one of the reasons that diesel engines have lower RPM lugging power than gas.

Bunk · Jan 4, 2006

This comment is more from practice than theory. I've had a new L4400 for about 10 hours that I've been using for yarding firewood in Maine. I'm generally running between 1200-1700 rpm's for most facets of the work, and the tractor has yet to break a sweat. I agree with the rest of the crew that it seems counter-intuitive to run rpm's up to 24-2600 if the job can be done successfully at lower rpms. Perhaps its the echo of my father's voice yelling "don't race the engine"! Good luck with the L4400. In my brief experience, it's a grat tractor.

btolle · Jan 5, 2006

With my B7510 I generally run about 1,700 RPM for loader work, sometimes if I am digging in hard material or traveling a long way with the load I will kick it up to 2,000 or so.

I go more by what "feels and sounds right" rather than the tachometer.

The only time I use PTO speed is when bush hogging and that is to keep the cutter speed up. Actually, I run a little below what the tach says even then.

As long as the machine is doing the job and not lugging you are probably using the right RPM's. If you are able to do most of your work at 1,200-1,300 then you are probably right about being overpowered but that is better than being underpowered.

Bill Tolle

ccsial · Jan 5, 2006

( I was advised to operate at the 540 PTO RPM something in the neighborhood of 2600RPM, even when not using a PTO implement ) 

I was advised by a Kubota rep to always run at PTO speed with the HST. That would not apply to a gear tractor. I usually run my 1910 around 1500 if I'm not using the PTO.

I always run my L3400 around 2000 if not using the PTO since the HST doesn't whine near as much as it does at 1500.