Gas vs Diesel Hp vs Torque

[workinallthetime]

Someone wrote in wanting us tractor guys to explain about horsepower and it got way out off track so I thought I would start this one.

I say if you working use a diesel and playing use gas burner. I justify my claims by cost of a diesel engine both up front and throughout its life, the diesel will last longer but maintenance is more expensive than a gas engine. I am talking about trucks here which pull your tractors around. If you dont need to pull over 10k then I dont see the need in buying a diesel, however if you do pull 10k and up buy a diesel or buy a pull truck built to pull.
I see no comparison in a 23 hp briggs engine (gas) and a 23 hp kubota diesel. both have 23 hp but one looks like it belongs on a lawnboy. I have owned a MF 175, JD 301a, and now a kubota bx23. My next puchase will be a kubota zd321 then maybe a larger 34-45 hp tlb.

bend to fit paint to match

 

[Doc_Bob]

What is the question?
Bob

 

[workinallthetime]

whats more important hp or torque
which is better gas or diesel

 

[art]

It takes torque to move things, so give me torque!

 

[MossRoad]

I have a 25HP Kohler gas engine in my little PT425. I'll bet your BX23 will pull me around all day. But I bet my PT425 will move a 20 yard pile of mulch or gravel 100 yards in half the time it takes your BX23 with less lawn damage.

Each tool has its use.

 

[GaryCrowell]

These torque vs. HP questions come up quite a bit and they always generate a bunch of misleading answers. You can't have "torque vs. HP", torque is a component of horsepower. Horsepower is essentially the rate at which torque is applied. The physics equation to calculate horsepower is: HP=torque x RPM/5252. In the end, horsepower is what counts, everything else is done through gear ratios. Go to a heavy equipment dealer and spec out a bulldozer, no where will you find the engine's torque mentioned unless you look in the maintenance manuals. The dozers are always catagorized by horsepower. Horsepower is what does work. Look at the gas turbine engine in a M1 abrams tank, it's pretty small and doesn't put out much torque, but it spins at about 13000 rpm's so it's got about 1500 HP and it gets that 30+ ton tank moving pretty well.

Compare your two 23 HP engines, the one in the lawnmower has the capacity to do as much work as the much bigger diesel in the tractor, that's just a physical fact. You could switch the lawnmower engine into the tractor and, for a few minutes anyway, it would do the same thing as the tractor's original motor. However, it certainly wouldn't be optimal for several reasons. First, you'd have a much more unforgiving power band. In order for the small gas engine to make the 23 horsepower it has to run at a high RPM, vary that RPM by more than a few hundred and now it's not putting out 23 HP. In other words, it's got a very peaky powerband and if it's not kept at the top of it's powerband through gearing then it won't put out the horsepower you need to do the job, certainly not optimal for a tractor because you'd be shifting gears all the time to try and keep it moving. A diesel engine that puts out more torque will produce the same horsepower at a slower engine speed and the horsepower band will be much flatter than the small gas motor. The flatter horsepower band is much more user friendly from an operator's perspective. Second is obviously longevity, a small gas engine running at peak RPM's all day just isn't going to last very long, it's not built for that.

I don't know that I've explained it very well, but maybe it'll help to put to rest the "HP vs. torque" argument. Argueing HP vs. torque is a lot like asking whether you like oranges or fruit better, one has a component of the other. When trying to find an answer you first have to ask a reasonable question, and HP vs torque is misleading from the start, that's why you have these long winded posts that you get from that question.

 

[Egon]

Lets not confuse the question with practicality!

 

[Oleozz]

For me at least, you explained it very well and what you are saying makes sense.

I don't know that I've explained it very well, but maybe it'll help to put to rest the "HP vs. torque" argument. Argueing HP vs. torque is a lot like asking whether you like oranges or fruit better, one has a component of the other. When trying to find an answer you first have to ask a reasonable question, and HP vs torque is misleading from the start, that's why you have these long winded posts that you get from that question.[/quote]

 

[john_bud]

I have a 25HP Kohler gas engine in my little PT425. I'll bet your BX23 will pull me around all day. But I bet my PT425 will move a 20 yard pile of mulch or gravel 100 yards in half the time it takes your BX23 with less lawn damage.

Each tool has its use.

Each tool has its use! Too true.



Still, give me big gobs of torque down low, peaking at 1400 rpm and dropping less than 5% thru 3000 rpm . That's where I want my 10,000 pound equipment to operate. I'd also like huge piles of rapidly increasing HP from 3000 to 7500 rpm in a 2600 pound '33 Ford Vicky. Heck, if you can give me both all in one reliable engine --> I'd take that too!!

jb

 

[Doc_Bob]

whats more important hp or torque
which is better gas or diesel

Torque and diesel, if price no object.
Bob

 

[kenmac]

If you are asking if I would rather have an engine with more hp than torque my answer would be no ! (examples) do I want 500 hp & 300 ft lb of torque ? NO . .I would want 300 hp & 500 ft lb of torque. Torque comes about by having larger pistions & longer stroke. I'll take more torque over hp any day.

It takes torque to move things

 

[workinallthetime]

I have a 25HP Kohler gas engine in my little PT425. I'll bet your BX23 will pull me around all day. But I bet my PT425 will move a 20 yard pile of mulch or gravel 100 yards in half the time it takes your BX23 with less lawn damage.

Each tool has its use.

thats a cute little thing but so is my bx. As for the challenge if both had the same tires id say it you get done right behind me. Of corse if the the ground was soaked and we had to clear a path through the brush id pull you out so you could bring me some cold lemonade, while i finished. That thing would be great for alot of stuff unfortunatly nothing i do.

ohh and A-MEN Gary.

 

[knute_m]

I'm not sure why I'm even posting this, but . . .

Gasoline engines hit their maximum rated horse power at fairly high RPMs. Diesel engine horse power is fairly consistent over a range of very low RPMs to high RPMs. My little 20 hp diesel tractor can just loaf along, while my lawn tractor 20 hp gas engine must scream to perform the same work.

Fuel efficiency and engine life are closely tied to RPMs also.

They both have their places in our lives. My 20 hp diesel tractor cost nearly 10 times what my 20 hp gasoline lawn tractor cost. I would hope my little diesel tractor engine will outlive my gas tractor's engine by far more than 10 times.

Knute

 

[gemini5362]

Ok if horsepower is the same thing no matter whether diesel or what then why is it that my 15 horsepower b6100 kubota diesel tractor with a 60 inch mower deck will cut through all kinds of high thick grass with no problems. My 20 horsepower riding mower with a 36 inch deck will bog down and die in grass half as tall or half as thick. both of them were 6 speed and I believe the top speeds in 6th gear was not that much different. My gass mower had only to run a mower deck that was almost half the size. Could it be that my diesel kubota has more torque than the gas riding lawn mower and since torgue is what actually turns things that might be more important than the horsepower rating.

 

[Volfandt]

I've got alittle over 4 acres that I mow regularly and I've mowed this same property over the yrs with several gas engine L&G tractors, a small gas utility tractor w/a bush hog and now a small diesel engine SCUT and the diesel wins out in both performance and power.
A breakdown if you will:
1) the single cylinder 8hp WheelHorse w/36" deck (that I've still got btw) would do all 4 acres but take ALL DAY. If I didn't keep up with the back it would take 3 passes to get it down to 3". But it would do the job.

2) the twin cylinder 18hp Craftsman GT6000 w/44" deck would power through the taller grass easier than the WH but would still take 3 passes to get the neglected back down to 3".

3) the twin cylinder 23hp JD L130 w/48" deck would power through tall grass that would bog both the WH & Craftsman down but would still take 3 passes to get the neglected back down to 3".

In each case upping the hp improved my performance in these air cooled machines.

4) the 4 cylinder 22hp Ferguson TE20 w/5' bushhog would power through the neglected back and bring it down to 3" in one pass. It would also work with implements the L&G tractors couldn't budge. Needless to say, even tho it had one less hp than the JD, it probably produced twice the torque via the gearing which enabled it to out work the much smaller machine.

5) the 3 cylinder 22hp BX23 w/60" MMM can also power through the neglected back and bring it down to 3" in one pass and do it faster. I attribute this to the HST more so than it being a diesel but it is good to note that the diesel is doing the same job with one less cylinder and useing at least HALF as much fuel as the TE20 cutting the same property.

So in my simple analysis, with all things being the same (or similar), the higher the hp, the more work can be performed and in gasoline engines the higher the number of cylinders the more torque can be obtained. And when comparing diesel powered machines of the same or similar hp, they can produce the same amount of torque as the similar hp rated gasoline engine that has more cylinders BUT do it with less cylinders and use less fuel to do the same work.
In my case the diesel powered tractor gives me my best bang for the $$$'s

 

[indianaEPH]

Ok if horsepower is the same thing no matter whether diesel or what then why is it that my 15 horsepower b6100 kubota diesel tractor with a 60 inch mower deck will cut through all kinds of high thick grass with no problems. My 20 horsepower riding mower with a 36 inch deck will bog down and die in grass half as tall or half as thick. both of them were 6 speed and I believe the top speeds in 6th gear was not that much different. My gass mower had only to run a mower deck that was almost half the size. Could it be that my diesel kubota has more torque than the gas riding lawn mower and since torgue is what actually turns things that might be more important than the horsepower rating.

As said before HP is HP, no matter what type of engine it is produced with. Torque is Torque no matter what engine produces it. However, I think part of the confusion with this discussion rests on the people comparing the peak HP numbers. In the case above the 20HP lawn mower makes it's HP at high RPM. As the load on the machine increase (tall grass) the RPM is reduced and the eninge power output is also reduced substaintially(but torque goes up a bit). For the Kubota, the same applies but the load increase (tall grass) only slows the engine down a small amount because it's engine torque increases substaintially with a decrease in engine speed. Yes, the gas engine also increases torque but not by much. The engine Torque Curve (as a function on speed) , not just the peak number, is very important in how useful the an engine will be for it's intended application.

 

[workinallthetime]

Oh this is fun isnt it, lol. Since its much easier to find hp and torque for trucks I continue to use them for examples, a 360 hp 520 ftlb torque diesel engine in a 3/4 ton will pull more EFFICENTLY and with less shifting up and down then a 367 hp 375 ftlb torque gas engine. Now the cost difference is great between the 2 engines but for an engine that will mostly be doing work where the large amounts of torque are needed then the diesel is the obvious choice. This thread was started due to the post on "edumacte me on hp" and how the topic got way off, and i was also looking a jd z turn at home depot for 4000.00 with a 23 hp engine and comparing it to a 23 hp kubota. to me there is no comparison. I wish i could find torque numbers on both machines but i dont want to spend that much time searching the net.

if i could only figure out a way to hunt coyotes on my bx23 with my ar-15,lol

 

[john_bud]

Oh this is fun isnt it, lol. Since its much easier to find hp and torque for trucks I continue to use them for examples, a 360 hp 520 ftlb torque diesel engine in a 3/4 ton will pull more EFFICENTLY and with less shifting up and down then a 367 hp 375 ftlb torque gas engine. Now the cost difference is great between the 2 engines but for an engine that will mostly be doing work where the large amounts of torque are needed then the diesel is the obvious choice. This thread was started due to the post on "edumacte me on hp" and how the topic got way off, and i was also looking a jd z turn at home depot for 4000.00 with a 23 hp engine and comparing it to a 23 hp kubota. to me there is no comparison. I wish i could find torque numbers on both machines but i dont want to spend that much time searching the net.

if i could only figure out a way to hunt coyotes on my bx23 with my ar-15,lol

Actually, you made a great point -- maybe without knowing it. HP is HP and torque is torque. But the rpms are different.

A 25 hp gas kohler may make its hp at 3600 rpm. Torque = hp*5252/rpm = 25*5252/3600 = 36.4722 ft-lb.

A 25 hp diesel kubota may make its hp at 2600 rpm. Torque = 25*5252/2600 = 50.5 ft-lb.

Seems obvious which one has more uumph, at least to me.


Speaking of obvious, you put the cross hair just behind the shoulder in the middle of body mass and slowly squeeze the trigger. Don't rest your elbow on the steering wheel as the engine vibrations will make it harder get a steady hold. ;-)

jb

 

[Egon]

And check the trees and grass to get the direction and strength of the wind!

 

[john_bud]

And check the trees and grass to get the direction and strength of the wind!

Don't work around here. No leaves and the snow is covering the grass. :-(

And at -20F like it was this AM, I ain't going out to see which way my breath is blowing!!

jb