Torque vs Horsepower

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Look folks, my first job was with Electro Dynamics (Division of General Motors). They made locomotives, generators and electric motors -Really big ones. All work was done at IITRI (Illinois Institute of Technology Railroad Institute).

First, there's a good indication that people on this thread do not fully read the posts. Please go back, read the posts and try to comprehend what is being said. -Not just the first couple words you see.


When an integrator purchases a general purpose motor (let's say a 16 cyl Caterpillar) and if it does not produce the horsepower at ANY given RPM shown on the horsepower/torque curve then, I can guarantee the motor will be returned and repaired, refunded or, be the exhibit in a lawsuit.

Maybe people here don't know how to read graphs. Pick an RPM on the x-axis, go up to either the HP or Torque line and get the value for that parameter. Take the engine and use a governor to hold the RPM at that chosen speed then test the motor's actual HP. It better be within a a few percent of what the graph says. If it's not then, the dyno test is wrong or the engine has a problem. -End Of Story.

BTW: There are many ways to actually/reliably read the HP of a engine. In the 2000 HP units I once worked on, the engines were connected to a massive electrical generator. The generator was connected to massive resistance load boxes (taking-up a good amount of the parking lot). The engine was set with a governor to a particular RPM (almost always 1800 RPM), the load was increased until it could no longer maintain the set RPM. Using Voltage, resistance and the known efficiency of the generator, the Wattage could be determined. Watts and Horsepower have a direct conversion. When engines were tested like this, data points would sometimes be taken at 100 RPM increments for the manufacturers stated range of operation. If your idea of a dyno graph is something other than this, then, you are not really talking about a dyno graph. I can assure you with absolute 100% certainty that from the perspective of electrical or mechanical engineering, real dynographs are produced in this way or, they use some other mechanism to waste energy and measure it's output.

If a company like Kubota (who makes diesel generators for AC units and gensets) provided dyno graphs that did not represent the engine's HP at any given RPM on the graph, they would be buying back a lot of engines.
 
Originally Posted by RayCJ
When an integrator purchases a general purpose motor (let's say a 16 cyl Caterpillar) and if it does not produce the horsepower at ANY given RPM shown on the horsepower/torque curve then, I can guarantee the motor will be returned and repaired, refunded or, be the exhibit in a lawsuit.

Maybe people here don't know how to read graphs. Pick an RPM on the x-axis, go up to either the HP or Torque line and get the value for that parameter. Take the engine and use a governor to hold the RPM at that chosen speed then test the motor's actual HP. It better be within a a few percent of what the graph says. If it's not then, the dyno test is wrong or the engine has a problem. -End Of Story.


If the "governor" is trying to maintain a specific RPM setpoint, then the throttle will continue to open until the load on the engine equals it's actual maximum HP output capability - which will always be at wide open throttle..

When you made the comment: "If you take any single point on that graph it means that if you held the engine at that RPM, it would be able supply that given amount of torque for the whole time you keep the engine at that RPM." it's not applicable to basically every HP/torque curve you see published - which shows HP and T at WOT conditions[ vs RPM - just as I originally commented. If you decrease the load, then the torque output will also decrease in order to keep the engine at a constant RPM. Therefore, at any given engine RPM, the HP and T output is total function of the load on the engine and the corresponding throttle opening to maintain a constant RPM.

Your statement is not true unless there are specific conditions involved, like a "governor" that changes the throttle potion to maintain a constant RPM as load increases. Making that comment without any caveats is not true as I explained. Do you think an engine makes the same HP and T at a constant 4000 RPM if the throttle is at 15% open vs 100% open?
 
Not sure what the hangup is about throttle position and WOT but I do know, in the world of big engines, nobody cares. Integrators look at an application such as drilling, hoisting, pumping etc and they determine what rotational speeds are needed and how much horsepower is needed to perform the desired work. Next, they look at the dyno graphs of many engines and find ones that provide the amount of needed HP at the desired RPM. Finally, they will look at the BSFC charts to see how much fuel it will burn. Of course, other factors such as duty cycle, service rating etc are considered; as such, you look for an engine such that it will operate near it's mid-point RPM rating.

Your question about 15% vs 100% throttle etc does not make sense. If the prime mover is a turbine it might well be at near 100% throttle. -As long as it's capable of providing the required HP at the stated RPM, life is good.

I'm done... I don't know what point you're trying to prove -and am tired of trying to figure it out. The OP of this thread asked about Horsepower and Torque -and I've covered everything I can without giving physics lessons.

It seems you want to talk about WOT vs partial throttle and the deficiencies of IC engines. ... Have at it but I don't think it will help the OP understand HP and torque.
 
Originally Posted by RayCJ

Not sure what the hangup is about throttle position and WOT but I do know, in the world of big engines, nobody cares. Integrators look at an application such as drilling, hoisting, pumping etc and they determine what rotational speeds are needed and how much horsepower is needed to perform the desired work. Next, they look at the dyno graphs of many engines and find ones that provide the amount of needed HP at the desired RPM. Finally, they will look at the BSFC charts to see how much fuel it will burn. Of course, other factors such as duty cycle, service rating etc are considered; as such, you look for an engine such that it will operate near it's mid-point RPM rating.

Your question about 15% vs 100% throttle etc does not make sense. If the prime mover is a turbine it might well be at near 100% throttle. -As long as it's capable of providing the required HP at the stated RPM, life is good.

I'm done... I don't know what point you're trying to prove -and am tired of trying to figure it out. The OP of this thread asked about Horsepower and Torque -and I've covered everything I can without giving physics lessons.

It seems you want to talk about WOT vs partial throttle and the deficiencies of IC engines. ... Have at it but I don't think it will help the OP understand HP and torque.


People like him (not the quoted person, but who you are talking to) is why there is so much confusion in this area. The correct explanation has been given in this thread a few times and i have seen the stupid "hp is how fast you hit the wall and tq is how far you go through it" saying 3 times. People just keep incorrect stuff about subjects they know nothing about, but this is the internet. It made people smarter for a few years because they could google the right answers anytime they needed. Now it is easier to get the wrong answer because people would rather keep posting their lack of knowledge than actually read and learn.
 
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This reminds me why when a spectator inevitably asks me how much horsepower a Top Fuel engine makes, I just say "a lot". I do get a kick out of overhearing some of their theories as to what 'torque' and 'horsepower' represent, though.
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Originally Posted by RayCJ
Your question about 15% vs 100% throttle etc does not make sense.


I simply asked if you think any IC engine makes the same T and HP at a constant 4000 RPM when at 15% throttle as it does at 100% throttle (wide open). That"s what it sounds like from your comments. Yes or no, and why? The throttle is on an engine for a reason.
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Originally Posted by RayCJ
It seems you want to talk about WOT vs partial throttle and the deficiencies of IC engines. ... Have at it but I don't think it will help the OP understand HP and torque.


I'm not resonding to the OP. I'm talking about WOT because of the comments you've made that makes it sound like you believe an IC engine makes the same T and HP at a constant RPM no matter what the throttle setting is at. It doesn't work that way. The T and HP made is a direct function of engine load (ie, throttle opening) and RPM. It's impossible for an engine to make 400 HP at 5000 RPM at 25% throttle when it makes a max of 400 HP at 5000 RPM at wide open throttle (ie, the data point on an engine manufacturer's engine dyno chart).
 
Originally Posted by ZeeOSix
Originally Posted by CR94
Originally Posted by ZeeOSix
... If the engine produces 400 peak HP at WOT at say 5000 RPM, then with no load on the engine it will have a cracked open throttle at 5000 RPM and be producing about 20 HP. As the load goes down, so does the required torque to spin the engine at 5000 RPM ... therefore the HP also goes way down. ....
Huh?! With no load, output (brake) power is zero by definition. If you're talking IHP, that's another matter.
... If you hold the RPM at 5000 in neutral there's still the load from the internal friction of the engine. It still takes a small amount of crank HP to make an engine rotate by itself.
Of course it does, but you're still confusing brake power output with indicated power.
Brake power is net output you can measure with a dynamometer. Indicated power is the power put into the pistons, based on integrating actual pressure in the cylinder during compression and expansion strokes. Think P vs. V plots. The difference between brake power (BHP) and indicated power (IHP) is (primarily) friction power---which is incidentally not likely as small you're assuming.
 
Originally Posted by ZeeOSix
Originally Posted by RayCJ
Your question about 15% vs 100% throttle etc does not make sense.


I simply asked if you think any IC engine makes the same T and HP at a constant 4000 RPM when at 15% throttle as it does at 100% throttle (wide open). That"s what it sounds like from your comments. Yes or no, and why? The throttle is on an engine for a reason.
grin2.gif


Originally Posted by RayCJ
It seems you want to talk about WOT vs partial throttle and the deficiencies of IC engines. ... Have at it but I don't think it will help the OP understand HP and torque.


I'm not resonding to the OP. I'm talking about WOT because of the comments you've made that makes it sound like you believe an IC engine makes the same T and HP at a constant RPM no matter what the throttle setting is at. It doesn't work that way. The T and HP made is a direct function of engine load (ie, throttle opening) and RPM. It's impossible for an engine to make 400 HP at 5000 RPM at 25% throttle when it makes a max of 400 HP at 5000 RPM at wide open throttle (ie, the data point on an engine manufacturer's engine dyno chart).


Of course it makes less power at less throttle. I never saw anywhere that he indicated otherwise. Most Dyno charts we see indicate max power at max effort. If you need less you use less throttle, if you need more you need a different engine.
 
Originally Posted by CR94
Originally Posted by ZeeOSix
Originally Posted by CR94
Originally Posted by ZeeOSix
... If the engine produces 400 peak HP at WOT at say 5000 RPM, then with no load on the engine it will have a cracked open throttle at 5000 RPM and be producing about 20 HP. As the load goes down, so does the required torque to spin the engine at 5000 RPM ... therefore the HP also goes way down. ....
Huh?! With no load, output (brake) power is zero by definition. If you're talking IHP, that's another matter.
... If you hold the RPM at 5000 in neutral there's still the load from the internal friction of the engine. It still takes a small amount of crank HP to make an engine rotate by itself.
Of course it does, but you're still confusing brake power output with indicated power.


I'm not confused about anything - you're trying to go off on a tangent from my original point of my comments. Go back to the original post where I mentioned WOT. I never once mentioned the words brake or indicated HP in any of my posts because I wasn't discussing them or how they differ.

I simply made a statement that an engine has internal friction and it still takes some power to make it run (overcome internal friction) at 4000 RPM in neutral with a small throttle opening. That was simply an example where the HP developed by the engine at 4000 RPM is not a constant regardless of throttle opening like some seem to believe, but in reality the HP and T is dependant on the throttle opening, which equates to engine load.
 
Originally Posted by 4x4le
Of course it makes less power at less throttle. I never saw anywhere that he indicated otherwise. Most Dyno charts we see indicate max power at max effort. If you need less you use less throttle, if you need more you need a different engine.


How do you explain the response of "No. At any point along the line - not necessarily at WOT." to the comment of "Only at wde open throttle of course." I take it he believes that no matter what the throttle is set at, an engine will always make the same HP at constant RPM point. Obviously it doesn't work like that as you know what a throttle is for - to regulate power output at any given RPM.

When was the last time you saw any manufacturer's engine dyno chart or a chassis dyno run chart done at less than WOT? If the discussion of HP and T curves deviates from the WOT case, then the discussion is a different animal.

https://www.bobistheoilguy.com/foru...6571/re-torque-vs-horsepower#Post5186571
 
The quote you had of him, he said it was capable of providing that power ect

You then added in only at wot

He said no
---

I can see how it can be read both ways. The capability is there wot or not but it wont be making it unless at max effort (wot, max fueling, full boost or whatever determining factors are required for the engine to be at max effort.)

How did he mean it? I cant be sure.

All i know is about 80% of the discussion of this thread has done nothing but make a relatively simple to understand yet widely misunderstood subject harder to understand from there being too much noise. The discussion could have been over by page 1 or 2 but here we are.
 
Originally Posted by 4x4le
The quote you had of him, he said it was capable of providing that power ect

You then added in only at wot

He said no
---

I can see how it can be read both ways. The capability is there wot or not but it wont be making it unless at max effort (wot, max fueling, full boost or whatever determining factors are required for the engine to be at max effort.)

How did he mean it? I cant be sure.

All i know is about 80% of the discussion of this thread has done nothing but make a relatively simple to understand yet widely misunderstood subject harder to understand from there being too much noise. The discussion could have been over by page 1 or 2 but here we are.


Well, the HP and T graph was certainly at WOT (they always are), yet the discussion went farther with clarifications and examples and still no agreement that it only happens ay WOT. Therefore, you can see why the conclusion. Oh well, yes I agree with you that these HP and T discussions are widely misunderstood - seen it on chat boards for decades. At least it's entertaining at times.
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Take an engine like I cited above that's connected to an electrical generator and load box. Assume the manufacturer says the effective RPM range is 300 to 2400 RPM.

1) Set the governor to 300 RPM.
2) Increase load until engine cannot maintain RPM.
3) Take measurements for load calculations.
4) Set governor 100 or 200 RPM higher.
5) Repeat step 2-4 until you hit the top range of the engine.
6) Perform calculations and plot data on a graph.

I can guarantee that at the lower RPM range of the engine, the "throttle" will be nowhere near wide open before it bogs down!!! The above procedure is representative of a REAL dyno test... the kind that will keep you out of litigation. [BTW: While the above tests are being completed, very precise fuel consumption tests are performed to calculate BSFC data].

If you are doing some sort of testing using a dynomometer that requires a constant wide open throttle then, I have no idea what you are really doing. -Do not call it a real dynomometer test because it is not! Maybe you are perverting some sort of procedure similar to a dyno test that simulates someone in a 1/8 or 1/4 mile dragstip run.... I don't know. Whatever, it is not a true dyno test.

... Oh how I wish I still had my notebooks from 40 years ago where all the results from many of these tests were logged. I can assure you, there were no annotations or the slightest bit of concern about the throttle position.

-Done!
 
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#2 is where I am getting confused. This is precisely how I tuned engines but I used eddy currents instead of a generator and load boxes. If the load increased at a rate that bogged the engine before the throttle was opened up then something in that test isnt right. Perhaps the engine isnt rated for those load levels at those rpms?
 
RayCJ...yes, when we were doing dyno testing at university, it was steady state, plot a curve.

The fact that modern chassis and engine dynos sweep through the RPM range either means that the true power isn't measured (some is used to accelerate for that couple of seconds), or there's fudges in there.
 
Originally Posted by RayCJ
... The OP of this thread asked about Horsepower and Torque -and I've covered everything I can without giving physics lessons. ...


Regarding the understanding of Tq and HP, and the concept of Force, I honestly think that a physics lesson would be helpful, and I tired to do that, but it pretty much went ignored.

It boils down to this in simple concepts:
- most prime movers (engines and motors) generate power in a rotational form; that rotation is converted to linear displacement via a vehicle drive-train (car, truck, motorcycle, train, tractor, etc)
- work is a concept of force applied to displace something from one location to another; it takes "force" to move (or stop) something
- torque is not a force; it is a product of force applied at a distance (the UoM are the same as "work", but it's not the same concept. It's not accurate to call torque "work" any more than it is to call it "force"; it is neither. Torque is applied at a distance; work is applied over a distance (aka displacement)).
- power is a concept of work per unit of time; the more powerful something is, the quicker the work gets done
- "horsepower" is an arbitrary term conjured up to attempt to put layman's understanding into a physical power condition; it merely speaks to a specific amount of torque at a specified rpm (for this conversation)
- acceleration is independent of displacement, although it can cause displacement; it is a concept of the rate of change of velocity and is a component of force, along with mass.

This is simple science, not rocket science. Yet it seems to be over the heads of many. Many whom live in the physical world, don't understand basic physics.
 
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Originally Posted by 4x4le
#2 is where I am getting confused. This is precisely how I tuned engines but I used eddy currents instead of a generator and load boxes. If the load increased at a rate that bogged the engine before the throttle was opened up then something in that test isnt right. Perhaps the engine isnt rated for those load levels at those rpms?


To add, in a setup with an engine on a brake dyno that holds the RPM constant, every engine I've ever seen is going to produce max power at that RPM when at wide open throttle. Torque and the corresponding HP produced at each RPM point is a direct function of cylinder air charging and optimum A/F ratio, and maximum air charging can only happen at WOT.

Max torque typically occurs at lower RPM than pesk HP on gasoline engines. Peak T coincides with the RPM of highest engine VE where the cylinders are getting max air charge.
 
Originally Posted by 4x4le
#2 is where I am getting confused. This is precisely how I tuned engines but I used eddy currents instead of a generator and load boxes. If the load increased at a rate that bogged the engine before the throttle was opened up then something in that test isnt right. Perhaps the engine isnt rated for those load levels at those rpms?


4x4le... Sorry for the slow reply. During the day, I do not have Internet access...

In many cases, the purpose of the tests I outlined was to establish the rating for the engine -not to test it against known values... The values were often not known. These devices were $pecial-purpo$e, to be used in places like the railroads, public utilities, mining industry etc. As such, the results had to be verified by at least 2 independent (and accredited) labs. In some cases, the reports were ultimately submitted to government agencies like the Dept of Transportation, Dept of Energy etc. That said, the goal was not to find-out if the engine was a perfect representation of the Otto cycle... the purpose was to test it under real conditions, not a 5 second zip through the RPM range.

Also, the steps I outlined were slightly simplified for the purpose of this discussion. In reality, a protocol, written and reviewed by the senior engineers (I was fresh out of college), was followed. This involved specified amounts of warm-up time, specified amounts of time under load at each RPM step etc... Significant effort went into fuel measurement. If any test could not be done according to protocol and schedule, all data was scrapped and re-done from scratch.

As for the WOT situation... There were many kinds of engines, most 4 stroke diesel, some 2 stroke diesel. Some turbocharged, some supercharged, some NA, some intercooled -and some engines were turboshafts (i.e. jet engine). All bets are off making assumptions about WOT and what the engine is supposed to be doing.


Originally Posted by Shannow
RayCJ...yes, when we were doing dyno testing at university, it was steady state, plot a curve.

The fact that modern chassis and engine dynos sweep through the RPM range either means that the true power isn't measured (some is used to accelerate for that couple of seconds), or there's fudges in there.


It's been a long time since I did this kind of work but, I'm pretty suspicious of these dyno-sweeps. I've also done a little investigation about the "inertia" dynos and they have me scratching my head.. You say there is a little fudging going on... I tend to think there's a whole chocolate factory's worth of fudge going on. I'm not seeing the light or feeling the love. Would love to tell you about a childhood story about "scratching heads" -but I think it might be over the top given the "complexity" of this thread.


Ray
 
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When I see a dyno chart that shows an engine makes more power with less then WOT then I'll believe it. Maybe I should be driving my car at only 75% throttle when going down the drag strip.
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Throttle position = amount of air ingested. More air = more power if the A/F ratio is optimum at all times for power production.
 
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