Comparison LS XG 3140 HP specs are wrong

polemidis · Mar 22, 2019

I am reading from the manual:
Maximum torque: 134Nm @1600rpm
Engine Rated Power: 29.88kW@2600rpm (39.96Hp@2600)

That simply does not make sense. Do they mis-advertise their product?

The formula for power/torque is Hp = Nm x rpm / 9550, so
torque= power * 9550/ rpm => 39.96Hp/2600rpm*9550= 146.77Nm

So either I am wrong in my simple calculation, or they advertise more Horsepower, or they advertise less max torque. Can you help me clear this out plz?

Jstpssng · Mar 22, 2019

Are both referring to engine horsepower, or is the first the rating at the PTO?

polemidis · Mar 22, 2019

Its clearly on the engine specs.

chim · Mar 22, 2019

One HP = 746 W

So in round numbers 40 HP x .746=29.8KW

George2615 · Mar 22, 2019

The difference is the RPM's. It makes max torque @ 1600 RPM but max HP @2600 RPM's. It doesn't make max HP and Torque at the same RPM.. At max torque of 1600 RPM it is only making 22.45HP based on the formulas in post 1.

finn1 · Mar 23, 2019

Peak torque always occurs at a lower rpm than peak power. That is, as the engine lugs down from rated speed /power under load, the torque increases.

Without this feature, called torque rise, the engine would fall on its face when the load increases under heavy load, such as pulling a ground engaging implement.

15% torque rise used to be considered a desirable torque rise target for farm equipment.

polemidis · Mar 23, 2019

Guys I think I didnt stated very clear the issue.
If what they rated the engine for is true, then the torque at 2600rpm is calculated at 146Nm which is more than the stated as MAX at 1600rpm as 134Nm

146 is more than 134! So either they overrated the HP at 2600rpm or the max torque at 1600rpm is underrated

TMGT · Mar 23, 2019

Do all your conversion first then calculate, less chance for errors. I noticed you mixed units of measure in your equation which gave you an inaccurate solution.

I came up with:
@ 1600RPM 30.1hp and 98.83 ft.lbs

@ 2600 rpm 39.96 hp and 80.7 ft.lbs

Sounds right to me

polemidis · Mar 23, 2019

TMGT said:
Do all your conversion first then calculate, less chance for errors.

I came up with:
@ 1600RPM 30.1hp and 98.83 ft.lbs

@ 2600 rpm 39.96 hp and 80.7 ft.lbs

Sounds right to me

wtf, I did the calculations in ft. lbs and it sounds good to me too. where am I screwing up? My calculations on my 1st post in Nm still look fine! argggg.

What I am really trying to find is the size/timings of the cylinders for a backhoe that I am designing. And I want to make a good estimation on the hp availabilty and if it worth to use a pto pump instead of the remotes.

TMGT · Mar 23, 2019

"HP=NM x RPM/9550" is wrong, that should be either "Kw=NM x RPM/9550" or "HP=Ft.Lb x RPM/5252"

polemidis · Mar 23, 2019

TMGT said:
"HP=NM x RPM/9550" is wrong, that should be either "Kw=NM x RPM/9550" or "HP=Ft.Lb x RPM/5252"

Ok thanks man, I know I am not loosing it yet. I got this formula online, obviously is a mistype https://getcalc.com/formula/electrical/horsepower-hp-torque.png

TheMadOne · Mar 23, 2019

polemidis said:
wtf, I did the calculations in ft. lbs and it sounds good to me too. where am I screwing up? My calculations on my 1st post in Nm still look fine! argggg.

What I am really trying to find is the size/timings of the cylinders for a backhoe that I am designing. And I want to make a good estimation on the hp availabilty and if it worth to use a pto pump instead of the remotes.

I'm not really sure what you mean by that. Listed pump flow for the XG3140 is 8.2GPM. Listed PTO HP is 32.

Here's a calculator that tells you how much HP you need to get a specific flow at a specific pressure:

Hydraulic Pump Calculations - Womack Machine Supply Company

Basically, you can get 16GPM to 2,700 PSI with 30.25HP. You would need a pump with 6.82ci displacement.

So you could have double the flow of the tractor outlets by using a PTO pump and still achieve a reasonable pressure...

Is that the info you were looking for?

They don't make 6.82ci pumps, at least not ones I could readily find.

Here's a 7.62ci one, which would be 17.81GPM at 2500psi.

7.62 cu in 16.6 GPM 54 RPM Dynamic GP-PTO-A-7-6-S Hydraulic PTO Pump | Dynamic | Brands | www.surpluscenter.com

TMGT · Mar 23, 2019

polemidis said:
Ok thanks man, I know I am not loosing it yet. I got this formula online, obviously is a mistype https://getcalc.com/formula/electrical/horsepower-hp-torque.png

That calculator is wrong on the bottom equation, it appears the P (power) should be Kw not HP.

I like online calculators for their speed but I won't trust one until I've done a full calculation to make sure they are accurate.

polemidis · Mar 23, 2019

TheMadOne said:
I'm not really sure what you mean by that. Listed pump flow for the XG3140 is 8.2GPM. Listed PTO HP is 32.

Here's a calculator that tells you how much HP you need to get a specific flow at a specific pressure:

Hydraulic Pump Calculations - Womack Machine Supply Company

Basically, you can get 16GPM to 2,700 PSI with 30.25HP. You would need a pump with 6.82ci displacement.

So you could have double the flow of the tractor outlets by using a PTO pump and still achieve a reasonable pressure...

Is that the info you were looking for?

They don't make 6.82ci pumps, at least not ones I could readily find.

Here's a 7.62ci one, which would be 17.81GPM at 2500psi.

7.62 cu in 16.6 GPM 54 RPM Dynamic GP-PTO-A-7-6-S Hydraulic PTO Pump | Dynamic | Brands | www.surpluscenter.com

You are exactly right!! But, the problem with these calculators is that they assume that the torque is constant as in a electric motor. With a gas or diesel engines thats not the case and one has to downsize the pump in order to actually handle the load. But another reason that I went deeper into this is because I do not want to run the tractor at the max power (at @2600 rpm) but at just above its max torque @1800, which conveniently will be more quiet too. I concluded that despite the fact that the 7.62ci is just above my tractor limits at 2600rpm(with a safety factor added) , its adequate to use at 1600 rpm, because the torque is higher (and hopefully at 1800rpm too.)
I am pretty sure that I will go with the 7.62ci. At 1800rpm I get 387rpm at the pto, 12gpm with the 7.62ci.
And the last reason is to see if I can make the backhoe stronger with wider cylinder bores. The stock LS backhoes are using 2.5" cylinders. If I can go with 3" without sacrifice speed, why not. I can also make longer backhoe.
Anyway it will take a while I just started a rough design 3 days ago

MHarryE · Mar 23, 2019

https://www.cm-labs.com/vortexstudi...tion/Content/Editor/editor_vs_torqueTable.png

You do realize that if you set your tractor to run at 1800 rpm with 2600 being high idle, you will be working on a different power curve as illustrated by this graph.

polemidis · Mar 24, 2019

MHarryE said:
https://www.cm-labs.com/vortexstudi...tion/Content/Editor/editor_vs_torqueTable.png

You do realize that if you set your tractor to run at 1800 rpm with 2600 being high idle, you will be working on a different power curve as illustrated by this graph.

No, I do not understand what you mean. I do not get what that graph shows. On my tractor, the top of the curve is at 1600rpm

NYCheese · Mar 25, 2019

MHarryE said:
https://www.cm-labs.com/vortexstudi...tion/Content/Editor/editor_vs_torqueTable.png

You do realize that if you set your tractor to run at 1800 rpm with 2600 being high idle, you will be working on a different power curve as illustrated by this graph.

Another thing to consider is that running a lot at 1800 rpm is going to cause way more regen cycles than running over 2k. When I bought my tractor last year, my first project was lots of backhoe work. I ran 16-1800 rpms for most of it, and hit my first regen at only 18hrs. I bumped up the throttle to 2200ish, and didn't trigger another regen until 63hrs. Just an example, and something else for you to consider.

polemidis · Mar 25, 2019

NYCheese said:
Another thing to consider is that running a lot at 1800 rpm is going to cause way more regen cycles than running over 2k. When I bought my tractor last year, my first project was lots of backhoe work. I ran 16-1800 rpms for most of it, and hit my first regen at only 18hrs. I bumped up the throttle to 2200ish, and didn't trigger another regen until 63hrs. Just an example, and something else for you to consider.

Thanx man! My regen periods are at about 50hrs, so far and I used the tractor mostly for log skidding or snow plowing. No standard rpm though. Maybe the contanst rpm on backhoe work makes it worse. Thank you , I will keep it in mind.