Oil & Fuel Diesel HP vs Gasoline HP

   / Diesel HP vs Gasoline HP #51  
This has sure been an interesting thread. Here's something that's been referred to, but not hit directly, unless I missed it (not unlikely...):

To simplify it as far as it can possibly be distilled to (by me - and all the old-timers here will tell you I'm not known for simplifying things!), torque is defined as a twisting force, while horsepower is defined as a specific amount of work over a specified amount of time. The key element here is the expression "over time". You can really only compare engines of different horsepower ratings if you're trying to compare the speed at which the work will get done. If you're trying to find out how much work they'll do, you better use torque, because it's the only one that measures what you want to know.

To repeat a story I've told here a few times: I was getting out of my '93 Dodge (Cummins, W250) in a WalMart parking lot a few years ago, just as a young (too young) guy was getting out of his jacked-up 350-powered Chevy with the obligatory performance-related stickers was getting out of his. I'm minding my own business and he says something like "Diesels!!! Good fuel economy, but if you want power you need a gas engine. I'll bet my 350 will blow the doors off your Cummins from a stop light any day." So I said, I'll take you up on that bet, if you'll back your gas engine up to my diesel, let me chain the hitches together. Then, if your hitch holds, after I drag your butt around the parking lot a few minutes, and rip the drivetrain out from under yours, I'll mosey on down to that stop light and be the only one in the race." He wasn't willing to accept the race on my terms, for some reason. But the conversation illustrates the point of this discussion. I have no doubt that his gas engine, with more hp, would take my diesel from a light. I also have no doubt whatsoever that my diesel with way more torque would drag his truck around backwards until it ran out of fuel (which would be long after his gas engine ran out, FWIW).

Another illustration of the same point: In '96 Edmunds (the car review and price guide people), did a "review" of the VW Passat. Their verdict (from an engine standpoint): the V6 was a very respectable performer, the 115hp gas engine barely adequate, but the 90hp diesel "woefully underpowered" (yes, those are quotation marks). Now, Car and Driver, more noted for Testarossa testing than VW diesel testing, also reviewed the 90hp TDI and said it easily ran away from the 115hp gas engine model and kept up with the V6 surprisingly well. In fact, if memory serves me correctly, they said it was only after the cars reached 70 or so mph that the V6 began to convincingly pull away. So, how did Edmunds blow it so badly? Simple: They didn't drive the diesel, and they forgot their basic physics. (I'm being charitable here by using the word "forgot" - privately I don't think the person who wrote the "review" ever knew the difference.) At any rate, confusion over the terms and what they mean is obviously very common, as this reviewer's huge mistake shows.

One last point: torque is always measured, while hp is always calculated (and no, I'm not forgetting that there are devices that "measure" hp and show it on a gauge - they're still calculating it). What's it calculated from? Why, torque, of course. And why is it calculated? Because time is the other half of the equation.
 
   / Diesel HP vs Gasoline HP #52  
</font><font color="blue" class="small">( One last point: torque is always measured, while hp is always calculated (and no, I'm not forgetting that there are devices that "measure" hp and show it on a gauge - they're still calculating it). )</font>

Neither HP (or Power) nor Torque can be measured directly. Even Force, Velocity/Speed/etc, Pressure, etc can't be measured directly. All these quantities are measured indirectly this way or that way. ACTUALLY, nothing on the earth can be measured directly. But there are basic quantities like Length, Time, Mass, Temperature which we can say they can be measured even though they are measured by using a "reference quantities." For ex., Greenwich in London sets the time Zero and the sun travel is taken as a reference period for one day and all times are measured according to this settings. So, except Length, Time, Mass, Temperature which use some references somewhere on the earth, all other quantities/parameters (velocity, pressure, force, torque, hp, heat, etc etc) are measured indirectly. or we can also say that they are "calculated automatically" in their measurement devices.

Having explained these; how is the torque measured? Remember that Torque = Force x Length = (Mass x Acceleration) x Length = Mass x (Velocity / Time) x Length = Mass x (Length / Time) / Time x Length = Mass x Length^2 / Time^2

Here, Mass uses a reference quantity kept at Paris - Length uses a certain amount of certain light wavelength and Time uses Greenwich zero set and Sun Travel.

So, Mass, Length and Time which are independent basical parameters/quantities are measured for a certain event and Torque is "calculated automatically" in the torque measurement device following this formula above. Another device can be made easily to measure HP or Power by dividing Torque by Time one more time (or in other words, multiplying Torque by RPM or Angular Velocity which has unit of 1/Time.)

Now, my question to those interested to learn;
You know the unit of Stress is PSI (or bar or pascal or etc)
Pressure units too are same, i.e. PSI, etc.
If so, then, whats the difference between them Pressure and Stress if same units are used for both of them?
Know this and have your lunch meal today on me;)
 
   / Diesel HP vs Gasoline HP #53  
Soundguy,
The main difference between say an old 20 hp tractor engine and a 20 hp briggs is the stroke length and the throw angle on the crank.
 
   / Diesel HP vs Gasoline HP #54  
The whole debate is not really about Gas versus Diesel. There are high torque Diesel engines and high speed Diesel Engines.
There are high torque Gas engines and High Speed Gas engines.
My Honda Van and my Ford truck both have 210 HP GAS engines.
The Van will take the truck any day of the week - Until I hook up the trailer with the tractor on it.
It comes down to Engine Design. Big Cylinders, Long Strokes, Heavy flywheels equal high torque.
Small Cylinders, and short strokes result in high revs. Light flywheels give fast throttle response.
1000 rpm @ 100 ft-lbs is the same HP as 10,000 RPM at 10 ft lbs.
Tractors need torque - therefore we use low RPM high torque engines with a wide power band.
HP sells lawn tractors, so they use higher revving, narrow powerband gas engines.
There are lots of high torque gas engines out there. Take a look at the old Gas Massey's. They'll out pull a lot of compact Diesels with more HP.
And there are a lot of 2 stroke dirt bikes out there with a lot more HP than any of our tractors, but unless they're spinning 7000rpm, they can't pull themselves. Now there's a narrow power band. Oh Oh - I just opened up the 2 stroke versus 4 stroke debate. Bye!
 
   / Diesel HP vs Gasoline HP #55  
At one of the pickup truck forums I learned this phrase and it stuck with me:

"You buy horsepower, but you drive torque"

I think the same philosophy applies to our tractors, no matter what the size. I have a JD335 with Kaw twin, 20HP and 54" deck. And a JD2210 with a 3-cyl Yanmar diesel with 17.7PTO HP and 62" deck. The 2210 will mow all day and never break a sweat. The 335 quickly lets you know when the going gets tough.
 
   / Diesel HP vs Gasoline HP #56  
</font><font color="blue" class="small">( "You buy horsepower, but you drive torque")</font>

Yes, if attachment behind your tractor has a gearbox or pulley which is powered/drived by PTO of tractor, then, it's very clear that there must be enough torque (not hp) to operate the attachment. But when pulling an attachment without a pulley or without a gearbox, then, the torque value applied by the tractor to the plow will be 0, yes, zero because tractor is pulling the plow in a linear motion with no-angle. How do you explain this?
 
   / Diesel HP vs Gasoline HP
  • Thread Starter
#57  
It really does not matter where the load on the machine comes from. It can be an attachment on the PTO, a plow on the 3pt, a hydraulic cylinder anywhere pulling power from the hydraulic pump, a road drag hooked to the drawbar, all 4 tires dragging the machine through mud, an A/C compressor, the left-hand turnung brake dragging, and is usually a combination of several of these examples and more. They all eventually pull their power off of the engines crank shaft. If there is not enough torque there for all their needs, it suddenly becomes much quieter.
 
   / Diesel HP vs Gasoline HP #59  
Dave, I'm not saying you are incorrect. Actually, everybodys telling correct. But I've got a feeling in this thread that people are confused about the terms. That was why I mentioned about zero-torque application on the plow. Indeed, the torque applied to the plow is zero - then, how comes the torque of tractor should be specified rather than the power? Remember the power will never be zero while the torque can be zero at some points/cases like in pulling. 2003Pilot's answer will clarify the things. Lets see;

2003Pilot said:
</font><font color="blue" class="small">( The torque is applied to the tractor wheels to make them turn and pull the implement.)</font>

You too are correct. (although the torque is still zero between the wheels and the plow) - Now, a new question arises; bigger size tractor wheels will be better than small size wheels to pull a plow or not?

Anyway, let me clarify the terms here-

Actually, rather than the torque, the FORCE is important as it does the work. Torque can sometimes be zero like in pulling the plow - but the force will not be zero.

I can put Power, Energy, Work, Torque, Moment, etc in the same category/group as all these are Force x Length in a certain time interval or in unit time interval. If that unit time interval is chosen as very small or infinitesimal, we call it as Power.

Remember;
Power = Torque x Angular Speed = Force x Speed

In pulling a plow, the Torque is zero. But, Power isn't zero (as angular speed in this case is at some infinite level) - so, you can't use the equation of Power = Torque x Angular Speed in linear motions like pulling a plow as infinity x zero = unknown.
In this case (in linear plow pulling), Power = Force x (linear) Speed is used.

As a conclusion, this is why Power HP is specified in tractors rather than the Torque which can be zero at some components of the engine. For ex., piston's motion is linear and the torque there is zero. However, the force on it the piston creates a torque, but it's created at the crank shaft. Force flows through the components sometimes creating a torque, sometimes doesn't create, but it still does Work (linear displacement) and if we take certain time interval, we can call it Power. Therefore, the Power is specified on tractor manuals. It's not for advertisement reasons. I prefer Power to be specified. But if we are really to chose another meaningful quantity, I'd chose Force rather than Torque.
 
   / Diesel HP vs Gasoline HP #60  
Nomad,
I am confused ?? here are a couple excerpts from your reply:

"Actually, rather than the torque, the FORCE is important as it does the work. Torque can sometimes be zero like in pulling the plow - but the force will not be zero."

Now this formula witch is the opposite or at least it appears that way to my feeble brain:

"Power = Torque x Angular Speed = Force x Speed"
 

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