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

 

[140Airpower]

SomptingGuy, IMHO, work/time is a physics definition of power and should be used. After all "work", "force", "distance", "velocity", "time, "power", etc all have formal definitions and don't make any sense or don't have consistent meaning if not used correctly or if a correct usage is not accepted. dwork/dtime is also fine.

Yoshimitsu, do you really hear people say that torque IS power at the low end? or do they say that high torque MEANS more power at the low end? The latter makes sense with respect to how engines are built and tuned.

I think some confusion is inevitable due to the fact that the piston IC engine is a tuned system that does not even exist as a working system at zero rpm and that is usually used over a restricted range of rpm with its torque and power depending on tuning choices (cam timing, sizes of ports and valves and lengths of ports). Other engines of limited power, like steam and electric, have the more logical relationship between torque and power with torque being highest at zero rpm and steadily decreasing with rpm while power remains relatively constant. BTW, if we look at a road vehicle as an engine (with variable gearing), it more closely approximates the constant power, diminishing torque characteristic.

 

[inline6]

i work for a company that develops vehicles for moving stuff and lots of it, we develop a tractive effort vs speed curve for each vehicle

most people will never understand the difference between power and torque because they dont take the time to try and learn it.

 

[yoshimitsuspeed]

inline6
Spending a lot of time trying to communicate with car guys, tuners and the general car community I think that so much of it is the education that they get from that community clouding the facts.
The fundamental basics of torque and power are pretty simple. My fiancee has a better understanding of it than most car guys do because she hasn't been taught her whole life that it means things it doesn't She just looks at the formula and a brief description you can find anywhere on the internet and she gets the basics. What frustrates me is that these other theories are so deeply imbedded in the car community that it makes it almost impossible for someone to accept the basic formula and principle and therefore the only way to make their world work is to separate the engineering/physics meaning of torque and power and automotive meaning of torque and power.

Tying into that.
140Airpower

There is a huge range but there are many people who believe that torque is power at the low end.
For example I started a similar thread on one of the car forums I am heavily involved in.
One of the questions in that thread.
It is obvious that the poster assumes that torque is low end power.
I had to explain that what really matters is where in the power curve the motor is when it exits the corner and that a torque increase at X RPM equals a power increase at X RPM.
You can tell that this poster is not terribly knowledgeable and accepts and understands that and that is fine.

Worse than that are the people who can actually make 300+HP/liter and therefore must know everything.
If you hang out on speed talk or similar forums you will see incredibly capable engine builders saying torque to mean low end power.

I realize this comes a lot from dyno tuning where people will look at peak power and peak torque as well as the OEMs listing those two datapoints for motors but it has lead to a belief in the automotive community that has imbedded it's self so deeply that even fairly educated people severely misuse the terms without even realizing it.
You will see this in car commercials. In fact I always laugh at the people who bust out the old saying power sells cars and torque wins races when I hear one of these pickup commercials that brag about the most torque in it's class. Who gives a damn? All that number is doing is selling cars.

You see it in magazines with big reputations like Road and Track, Car and driver etc.
They will write about how the torque output of the car as though it is low end power.
At least top gear jokes about torques as though it's something they may not totally understand but they still use torque to define low end power and power to define high end power.

 

[dicer]

Dynamometers measure torque at X rpm, and HP is calculated from that. Its just that simple.

 

[GregLocock]

The hardest thing to understand was the english. 8/8

you confuse power and work in one question, I do not understand why you won't use power as a word. work/time could be taken to mean work and/or time, for example.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[SomptingGuy]

Had this discussion before around these parts...

I think the confusion between the terms "torque" and "power" in general (non technical) usage is that journos and other writers need to correlate things with basic human senses, which are instantaneous things. I would argue that we are led to think that (for an IC engine at least) torque can be felt, power can be heard. That's what I read anyway. It's why petrol-heads don't like powerful quiet cars (can't sense what they think is power), even though they love the torque (can actually still feel that).

These are the only two base engine numbers we are given by manufacturers, which is not the fault of the journos. They have tried using other numbers (in-gear acceleration times, standing-start acceleration times, top speed), but these are all application related, not base engine and always qualified and explained to the point of boredom.

I'm amused by the extra confusion added by electric motors that are current limited and virtually silent. The journos really haven't managed to accommodate them yet other than to note that they have a lot of low speed torque.

- Steve

 

[Deividas]

Pretty good video about torque and power:

https://www.youtube.com/watch?v=fgLNO3ThGD4

 

[SomptingGuy]

Maybe as engineers we should come up with some new quantities to throw around. How about dWork/dPosition? That kind of stirs in everything except time. How much kinetic energy can you add to your vehicle in a given distance?



- Steve

 

[Tmoose]

"Dynamometers measure torque at X rpm, and HP is calculated from that. Its just that simple."

But it looks like the inertia dyno industry does something a little different. Land and Sea is a former Massachusetts dyno company (now in Concord NH) that makes a bunch of products including stuff to instrument old dynos of different types.
They say this -

http://www.land-and-sea.com/dynamometer/dynamometer-comparison.htm

inertia-only "dynos" can not directly measure torque or maintain a steady state load (without also being equipped with some form of absorber and load cell or a parasitic drag source (e.g. a large fan or pump with a known loss curve).



This guy says it is common for inertia dyno software to monitor roller rpm over time, and for standard software to think of the energy at each rpm (after the operator enters all the inertias in the system.)

http://www.dtec.net.au/Inertia Dyno Design Guide.htm

"Calculate the energy of rotation for each of these angular velocity’s (sic) using the flywheels moment of inertia and then the change (Delta) in energy of rotation between these 2 points."

the "energy of rotation" has sissy metric units of Joules.
- One conversion is 1 joule = 0.74 pound-force foot. It is technically "work," not torque, even though the ft x lb units are mathematically the same ( work is force exerted through some distance, like a 216 pound Timberlake climbing up 40 feet of stairs at 5 Neponsett St. (pound-force is not pound-mass. High tech stuff that thinks of lbs as mass needs a correction factor and is confusing as heck)
- Another conversion is 1000 joule = 0.000372506 horsepower X hour, or 0.536 horsepower X second. So all we have to do is divide the energy change by the time increment in seconds and we do get HP directly.

 

[yoshimitsuspeed]

dicer
Like Tmoose said
Load based dynos such as a water brake like Land and Sea manufacture do measure torque and RPM but you are still measuring for power. Without both torque and RPM you have nothing. Once you have torque and RPM you have power.

In the automotive world most dynos are inertial dynos and they measure the rate of acceleration of the fixed mass.


GregLocock

You mean it was hard to understand the wording in the last question? 8/8?

In which question do I confuse power and work?

SomptingGuy
I do not think it's that complicated for the most part.
I am not trying to suggest using more complex terminology or concepts.
I just want to see small changes. Instead of the journalist saying you can really feel that torque in the corners of X car but the power that y car makes on the straights is much better for them to understand and express that x car makes better low end power and car y has stronger top end power.
The biggest problem for me is when people try to compare torque and power or use torque to mean low end power.

 

[GregLocock]

No, it was hard to understand (or at least not properly written) all the way through.


i don't know which question it was, you look for the one where you've confused power and work, and that's the one



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[yoshimitsuspeed]

Well that doesn't do me much good.
If you have any specific suggestions on how to improve it I would love to hear it.

At one point I did have the questions just stated as work but after several suggestions I changed it to work/time which most agree is equivalent to saying power without saying power.
The point of not using power is trying to remove the words that already have such deeply ingrained beliefs and use synonyms or technical descriptions to show the principles without the pre existing judgement. It's also trying to get people to see that the work/time is what is actually important when trying to figure out how much work a motor can do.
Unfortunately it even between engineers, physicists and the like it seems almost impossible to come to complete agreement on terminology.

Some say that work/time is not an accurate or acceptable term for power while many others and many sources give work/time as the textbook definition of power.
At this point I have given up on making everyone 100% happy but I am still open to suggestions that could make it more accurate and technically correct.

 

[gruntguru]

- Energy/time is certainly the definition of power. dE/dt is instantaneous power whereas E/t is average power.
- SOME (not all) dynamometers measure torque and speed, some measure Volts and Amps, some measure force and velocity.
- Power is a universal number which is constant and can be measured all the way from the fuel tank. Fuel flow rate can be expressed as power, and all the energy can be tracked to its final destinations eg work to propel the car, heat from the exhaust, heat from the cooling system, unburned fuel in the exhaust etc etc. All vehicles need power to accelerate, but torque is optional (ever seen a rocket car?)

je suis charlie

 

[140Airpower]

gruhtguru, torque is not optional if we are in a wheel-driven vehicle. Otherwise it is optional. Even force and displacement could be optional, but not for vehicles.

 

[140Airpower]

Yoshimitsu, you comment on a very interesting quote: "...For example I started a similar thread on one of the car forums I am heavily involved in.
One of the questions in that thread.
Quote (So would an engine that produces more torque exit a corner faster than a higher strung engine? all else being equal.)
It is obvious that the poster assumes that torque is low end power...".

Yes, I have often heard this kind of talk. But, I never thought of it as implying that torque IS power. I always visualize the torque and power curves of engines with "low end grunt" compared to engines with "high end power" and understood there was a trade off of better acceleration out of corners vs higher top speed. The idea is you can relate these engine characteristics with those torque and power charts. I assumed the speakers knew the difference and that their comments made sense. Maybe your quiz shows differently.

 

[140Airpower]

Tmoose, why do you say "sissy" metric system? Is it that it's a system for people who object to confusion, time wasting and error generation? If so, I agree. Real engineers should not flinch at "roughing it" with the good old avoirdupois, English, American jumble.

 

[yoshimitsuspeed]

140Airpower
You are right in that on a dyno graph the torque will be higher in the lower RPM and I believe this is part of what leads to this misconception but yeah there are a lot of people out there tho think that torque is low end power and many do not even equate the two being tied together by any formula but see them as two separate entities creating many misconceptions.
V8s make torque but 4 cylinders make power.
torque is better in the corners but power is better in the straights.
A 250 hp GSXR motor won't accelerate a car well because it doesn't make enough torque and you need torque to accelerate heavier vehicles.
Diesels are better for big trucks and towing because they make more torque.

If I ever get rich I am going to drop a high strung small displacement motor in a box truck, play with some gear ratios and a few other tweaks and race it up a pass against something like a 7.3 IDI such as the one sitting in my 26' Uhaul. Sure it would have a little more trouble getting off the line, sure it would go through clutches faster, sure it would need rebuilds more often but I just want to do it to see the look on peoples faces when some little sportbike motor or small built econobox motor beats the massive diesel to the top. There are a lot of people who's worlds would come completely undone. Many would believe that somehow you rigged or fixed it but oh well.

 

[BrianPetersen]

Just because the bike engine makes enough power doesn't mean it is the most suitable for the application.

 

[yoshimitsuspeed]

No I'm not saying it is by any means but not for the reasons that most people believe.

 

[gruntguru]

140Airpower "torque is not optional if we are in a wheel-driven vehicle. Otherwise it is optional. Even force and displacement could be optional, but not for vehicles."

True, but the question most people don't ask is "what is the ultimate purpose of that torque?" and the answer is "to generate linear force, tractive effort, whatever you want to call it".

A chassis dyno cannot measure torque, because a car does not apply torque to the road surface.

je suis charlie