Torque and power quiz 4

[yoshimitsuspeed]

I spend a lot of time in the automotive community and a lot of time on car forums and groups.
Ever since I started to learn the actual relationship of torque and power it drove me crazy how few others in the automotive world actually understood this basic formula. People capable of building motors that make 500 hp per liter and who still think that torque is low end power.
I have gotten into enough arguments with people to learn that most would rather argue relentlessly cause that's what theys daddy taught them than sit down and think about the simplicity of the formula long enough to understand the relationship of the two.
I have decided to try a different tact and make a little quiz that gets people thinking about this from a different angle and maybe hoping they will get the point that torque and power can't be compared, and that torque does not mean low end power.
I just started on this tonight and it's 3AM. I want to do more to improve it but I also would love some input from others on ways I could improve it.
I would like it to be as detailed and informative as possible while still being interesting and keeping the person engaged and interested.

Tell me what you think of what I have so far.
What could I do better?
What are other questions I could ask or ways I could put things to get people thinking about the relationship without getting too bogged down in the math to loose too many people?
On that note should I focus more on the math or stay more with the basic relationship and principles?

http://matrixgarage.com/content/think-you-understand-torque-and-power

 

[FennLane]

Why do you believe that torque and horsepower cannot be compared?

They are simply two sides of the same coin and how you view the result depends entirely on the objective you are trying to fulfil. As you have stated the relationship between the two units is fixed and easily defined.

If your only objective is to accelerate a car at a maximum rate and you have complete control of gearing then it is clear that horsepower wins.

If you have huge weight and accel doesn't matter torque will probably win.

Look at the 10 HP Steam Roller which weighs 40 Tonnes and compare this to a 750 HP F1 car that used to go at 20000 rpm and only develop 300Nm of torque which is 'better'?

If you want to win a GP then clearly the F1 car. If you want to roll the tarmac on a 4:1 hill then the F1 car would look a bit silly.

The arguments in the Automotive world always start with the often quoted statement ' that Horsepower Sells cars and torque wins races'.

The weakness of the discussion that result are that they never state any basic cases of interest and are normally framed by a complete lack of understanding of the basic Physics.

It should also be clear that Tractive Effort would also be helpful in comparing two vehicles as gearing is taken into account.

Your quiz seems to start without any basic definition of what you are trying to prove.

Surely it is better to start with explanations of force, work, energy etc, etc and ensure that the basic groundwork has been covered thoroughly.

 

[yoshimitsuspeed]

They cannot be compared and they are definitely not two sides of the same coin. That insinuates the general misconception of what torque and power are.
200 lb ft of torque cannot be compared to 200 hp because they are completely different things. As far as moving a vehicle is concerned that 200 lb ft of torque means nothing until you determine the amount of work it can do over time.
The point of the quiz is trying to get people to understand the relationship of torque and power in regards to work. In the case of the steam roller I don't feel it's practical to compare a 10 hp motor to a 750 hp motor as that power isn't needed to do the job.
To illustrate a point like this I would have a tendency to compare something like the two motors in my horsepower graph.

The red line is a 1.6 liter 4AGE turbo.
The blue line is a detroit diesel.
In an ideal world I would like to find a smaller motor that had a little more low end power because in this example the detroit does have an advantage in the low end over the 4AGE but it still shows that the advantage is not directly connected to how much more torque the detroit makes.

http://matrixgarage.com/pictures/tq-power/torque-graph.png

Despite only having 30% as much average torque in the short term the 4AGE would do almost as well as the detroit at a job like hauling a semi truck as long as it had the proper gearing to take advantage of it's power curve.
The Detroit would be chosen not because it's torque is particularly important but because
1. it would suck needing to spin the 4AGE to 4000 RPM to get started.
2. The high RPMs would wear out the clutch and drivetrain much faster.
3. The 4AGE would probably need to be rebuilt every 20k to 50k miles when the Detroit would likely make it 200k to 500k miles.

In your example You could compare something of a similar capability but at another extreme. For example with the right gearing a 10 hp nitro RC motor would properl the steam roller just as well but all the above issues would make it a less ideal option. The 80 lb 1400 RPM diesel motor is not the choice directly because it makes more torque but because it will be quieter and last much longer.

I hate sayings like that and it's exactly that mentality that I am trying to get rid of. That saying is so flawed that it should be easily thrown by the waysaide yet people are so invested in this myth that torque wins races that in the automotive world torque means something completely different than it does in the world of science and physics.
You can sit down with someone and explain to them that a gearbox will multiply torque of a higher hp motor to apply more torque to the ground but they will never accept it even if you throw all the math and science available to them. They believe that automotive torque exists outside of math and physics and that is what I want to make people understand.
I want people to realize the stupid truck commericals that advertise "the most torque in it's class" are 100% sales propaganda to sell suckers on their car when it has nothing to do with how the vehicle will perform it's job.

I have been trying to decide what I want to do about more information.
I don't really want to get into the definitions before the test because that is what seems to get people defensive or disinterested in the first place.
I will probably do a brief intro along the lines of
Most people think they understand the relationship of torque and power but very few actually do. Do you?

I am open to suggestions on what the intro could be.

I would like to have more at the end though. I would like to show the math and or theory that supports the answer. Still haven't figured out how to do that in this program.
That way anyone who is actually interested in why they got a question wrong can have at least enough basic information to point them in the right direction and give them some understanding of why.

At the end I would also be tempted to post a link to something like this where someone has already taken the time to explain it better and in more detail than I would.

http://www.epi-eng.com/mechanical_engineering_basics/energy_and_work.htm

http://www.epi-eng.com/mechanical_engineering_basics/power_and_torque.htm

I appreciate your input and would love to see what others think about this.
I know that this is something that doesn't bother most people and the few others it does would rather not get into it with people who would rather remain in ignorant bliss than learn something new but this really is a major pet peeve of mine and does drive me crazy enough that I would like to do anything I can to try to get people to think about these things a little bit differently.
I am not the best at trying to teach or explain things so any input to improve would be very welcome.

 

[dgallup]

Well I got 7 out of 7, do I get a star?

While I agree the general population is confused about the difference between torque and power, I have given up trying to spread my knowledge to the great unwashed internet masses. I used to try to correct some of the bigger errors promulgated on internet forums only to find that the ignorant prefer to remain ignorant and are hostile toward anyone trying to point out the errors of their ways. It's like trying to teach a pig to sing, it's a waste of time and irritates the pig. Fortunately this forum, for the most part is different, and we can engage in educated discourse.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[yoshimitsuspeed]

dgallup
Gold star for you

I agree with everything you have said.
Unfortunately those same people are perfectly happy to spread that information to others.
I have for the most part stopped trying to change their mind but instead provide as much math and facts as I can hoping that I may sway someone with two brain cells to rub together to not just accept the other sides view just because it's the belief of the majority.

 

[yoshimitsuspeed]

Just added a few new questions and got more detailed answers at the end.
I wish I could get them to show up after the grading but you take what you can get I guess.

 

[Compositepro]

Taking this quiz reminded me of elementary school multiple choice science tests where the questions were written by "educators" that did not now much about science. I don't mean any insult. You need to start by clearly defining terms. If words have different interpretations to different people there can be no communication.

Work is mechanical energy and often the words are interchangeable. Power is energy produced per unit time. My ex-wife was somewhat technical with a degree in biology, but never really grasped what a unit of energy was or how that was different from power. Without understanding the concept of energy and being able to quantify it, there really cannot be any further useful discussion. The pig analogy is very appropriate.

Presenting data as a function of percentage of red line rpm without knowing what that red line rpm actually is, is meaningless.

When speaking of torque, is that at the flywheel, after the gearbox, or at the wheels. Is it max torque (at what rpm)? I do not think your quiz will help anyone.

 

[BrianPetersen]

The confusion often comes from the shape of the torque curve and the gearing that is conventionally applied.

In most automotive applications, a gasoline engine will often be geared so tall in the highway cruising gears, in the interest of economy, that at normal highway speed, it is running well below its torque peak. It will be necessary to downshift in order to get anywhere, but diesel engines are often geared right near their torque peak at normal highway speed.

VW gasoline versus diesel are like this; YES the gasoline engine version will outrun the diesel in a drag race, but the TDI will usually be more fuss-free in daily driving and not demanding of so many downshifts.

While the theoretical possibility might exist that you could use a F1 car engine to haul an 80,000 lb tractor-trailer with suitable gearing, in reality you don't want to do that.

 

[gruntguru]

Hi Yoshi. Looks good so far. I will try to think of some constructive suggestions. In the meantime a couple of nit-picks.
- Power is a measure of "work rate".
- Work is Energy, so power is also a measure of "energy rate" i.e. there are two correct answers for Q2
- It may be instructive to tell the examinees that Q3 and Q6 are the same three engines.

My summary of the torque/power debate.
1. The peak torque value for an engine (without rpm info) is useless.
2. The peak power value for an engine is useful.
3. Sure - the "torque curve" tells you everything, but if you have the torque curve, you know the power curve. As you point out, a torque curve drawn with a dimensionless speed scale (0% - 100% rpm) is useless. The equivalent power curve tells you (almost) everything you need to know.

je suis charlie

 

[yoshimitsuspeed]

Compositepro

The reason I am posting here is for input on how to improve it.

How would you suggest I change the wordage to look better and be more accurate?
My biggest issue is how do I bridge the gap and make these principles easily understandable by the common person who didn't go to school for physics or engineering. I want to use simple yet accurate and clear wording and explanations.
I had thought about putting something like power is a measurement of work over time. Would this sound better?

As for the percentage of RPM I agree with gruntguru and that was my point for doing it like this. In relation to torque that graph tells you nothing. People like to think that because their truck makes 1000 lb ft of torque that it will do magical things. They don't understand that this figure is meaningless until you add RPM. The whole point of the torque graph is to bust these people who will look at that graph and assume that the motor that makes the most torque will do the most work.
The question with the power graph does tell you a lot. Not as much as it would with units of RPM but you can clearly see which motor can do more work over time.

When I say X engine makes X torque I expect that it is pretty clear that is at the crank. Any time I am talking about a transmission or other point of measuring torque I feel I made it pretty clear. If you can point out a specific spot that stands out to you I can take a look at it.

BrianPeterse

Thanks for your input and those are the exact kind of points I am trying to make here.
You are right that various motors have pros and cons. Otherwise there would only be one type. I am trying to get people to understand that the reason for having a Powerstroke in your pickup is not that having 600 lb ft of torque is necessary to haul a heavy load and that the actual benefits are things like low average RPM, long life and less wear on the drivetrain.

gruntguru

Thanks, I think you summarized what I am trying to accomplish very well.

Do you think it would be better to clarify that power is work/time making that more technically accurate than saying it's just energy?
Or would it be better to give both a more accurate designation of work rate and energy rate and make them both acceptable? I would lean towards the former.

Im not sure if you saw it but I figured out how to add a detailed explanation of each of the questions after the quiz. If you haven't seen it yet I would love any input on that as well.
In there I pointed out that they are the same engines.
I went out of my way not to point this out in the quiz because in question 3 I just want people to see that fatty torque graph of the Detroit and assume that it must obviously be the most impressive motor.

 

[LionelHutz]

The scaling of the rpm is just plain confusing and it makes the quiz become more theoretical vs practical. I would provide the power and torque curves with real rpm for 2 engines, a low rpm diesel and a high rpm gas and then pose questions using that real data, such as which one would accelerate a 40,000lb semi truck faster? or why is the diesel more suited for use in a semi truck?

The simplest definitions/explanations of torque and hp to apply to vehicles I have come up with are as follows;

HP tells you how fast your engine can accelerate your car. The HP at the wheels is the HP at the engine minus the drivetrain losses. Put more average HP to the wheels and your car will accelerate faster.

Torque just tells you the twisting force your engine applies to the transmission input shaft. The torque is meaningless for telling you anything about how fast your car can accelerate without knowing the engine rpm. Once you start using both the torque and the rpm, you are really using the HP information, since HP is proportional to torque times rpm.

I believe that people are mostly stuck on the idea that the torque is higher below 5250rpm so it must be the more important number.

 

[gruntguru]

I think the dimensionless rpm scaling removes the ability to calculate to compare and makes a person think about the concepts of power and torque. So - a good thing.

je suis charlie

 

[Tmoose]

http://www.motortrend.com/roadtests...50_vs_ram_1500_chevrolet_silverado/specs.html

2.7 l 2015 EcoBoost Ford F150 - 325 hp @ 5,750 rpm, 375 lb-ft @ 3,000 rpm , 6 speed auto

3.0 l TurboDiesel Ram 1500, 240 hp @ 3,600 rpm and 420 lb-ft @ 2,000 rpm, "unflappable" 8 speed auto,
note 240 HP at 3600 rpm = 350 lb ft , so the diesel is making at most few % less torque than the eco boost around 3600 rpm.

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Compare all the acceleration tests, including DAVIS DAM "FRUSTRATION"** 50-70-mph passing acceleration with 1,000 pounds of payload

"The EcoDiesel's torque comes on quickly and makes it feel quicker than the Chevy around town. Part of that is due to its exclusive eight-speed automatic transmission, which we agreed was the best here by far. "It's unflappable," said Seabaugh. "It's never caught in the wrong gear. It makes the Ford's and especially the Chevy's six-speed transmissions feel like they're from an entirely different era."

 

[gruntguru]

Interesting set of numbers. One thing is for sure - the Ecoboost engine has a LOT more power than the other two - somebody's power claims are wrong. Not that I am a fan of turbochaged SI engines in trucks. Sounds like a recipe for reliability problems to me.

je suis charlie

 

[dgallup]

Interesting that they did the towing comparison with 7,000 lb trailers but the Ford towing capacity is only 5,000 lb.

Last year I bought a Ram 1500 with the 5.7 l Hemi mainly because of the ZF 8 speed transmission. Ford & GM were way behind on transmissions although GM is introducing an 8 speed this year and Ford is working on a 10 speed.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[yoshimitsuspeed]

Some stats from the first few days.
Every time I make changes to the quiz it makes a new revision so this is probably about 30% of the total test takers but all previous revisions had similar numbers.
The earlier ones had a little lower percentage above 40% and 5% to 6% passed. I believe some people may be taking the test multiple times. Another possibility is that some of the revisions have made the test a little clearer to some.
One interesting thing is that the 40-60% range is always the lowest. Right now it is tied with the 80% to 100% range but that's the highest it's gotten.
The incomplete tests are included in the 0-20% graph

 

[yoshimitsuspeed]

Oh and passing grade is 75% just because that was the default.

It also made me pretty happy my fiance got 7/8 right hehe.
She is not mechanically minded, her eyes glaze over when I start talking cars or motors.
Goes to show that some basic math skills and a bit of a brain really should be all it takes.

 

[BigClive]

How many of the "regulars" on this forum would admit they got any questions wrong?

 

[BrianPetersen]

I got question 2 wrong but I blame poor wording.

 

[SomptingGuy]

I don't like the use of "work/time" or work over time for power. Power is an instantaneous quantity, not usually time-averaged. dWork/dTime as dTime->0. It minimally needs the word "rate" in there.

- Steve