Think you understand the relationship of torque and power?

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yoshimitsuspeed
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Think you understand the relationship of torque and power?

Postby yoshimitsuspeed » Tue Feb 24, 2015 2:39 pm

I made up a little quiz to test peoples understanding of torque and power.
I am hoping this breaks down the math and science behind it in a way that can help people understand the theory without creating the reactive environment that always happens when trying to discuss the science.
The math and fundamental principals have been given the thumbs up by several engineers and several others who have a good understanding of the physics behind this so if you have a problem with any of the questions, answers or anything else address it with math, physics, and fundamental principals otherwise your complaint will be ignored.

I am always looking for ways to improve this and making it clear and understandable as possible so if you do have any educated suggestions please to post up. This is still a beta.

http://matrixgarage.com/content/think-y ... -and-power

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Re: Think you understand the relationship of torque and powe

Postby jondee86 » Tue Feb 24, 2015 5:53 pm

I fully support your efforts, so please understand the following comments
are intended to be constructive :)

Your intent for the first graphical question is too obscure for the average
punter... and I place myself in that category. This question will inevitably
generate a very high percentage of random selections as people simply
guess and move on to the next question.

The second to last question is a bit awkward. If you calculate hp from
the torque and rpm given, the answer is above 200, but if you back
calculate torque from the hp and rpm the answer is under 200. It would
require the same knowledge, but with less ambiguity, to select the correct
answer from a multiple choice of say...
How much torque will it make...
1. 225 ft-lb
2. 200 ft-lb
3. 175 ft-lb
4. Not enough information

Cheers... jondee86
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Re: Think you understand the relationship of torque and powe

Postby yoshimitsuspeed » Tue Feb 24, 2015 6:21 pm

jondee86 wrote:I fully support your efforts, so please understand the following comments
are intended to be constructive :)

Your intent for the first graphical question is too obscure for the average
punter... and I place myself in that category. This question will inevitably
generate a very high percentage of random selections as people simply
guess and move on to the next question.

The second to last question is a bit awkward. If you calculate hp from
the torque and rpm given, the answer is above 200, but if you back
calculate torque from the hp and rpm the answer is under 200. It would
require the same knowledge, but with less ambiguity, to select the correct
answer from a multiple choice of say...
How much torque will it make...
1. 225 ft-lb
2. 200 ft-lb
3. 175 ft-lb
4. Not enough information

Cheers... jondee86


I am always looking for input so yours is welcome.

The point of the graphical question is to try to get people to realize that torque without RPM means nothing. Anyone who thinks that torque wins races will automatically select the motor that makes the most torque and I specifically made this question to bust those people. If you have any suggestions on ways to accomplish the same goal while while being less ambiguous I would love to hear it.

For the other question what do you think about this?
If a motor makes 200 horsepower at 6000 RPM will it make more or less than 200 lb ft of torque at the same RPM?


I have been kind of trying to minimize actual mathematical calculation because a lot of people really seem to loose interest as soon as you bring that into play.
To answer this question all you need to know is that the formula is based around 5252 and before that torque is higher and after torque will be lower than power.
This is mostly meant to get people thinking about the fact that torque will read higher in the lower RPM purely because of the formula that this relationship is based on.

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Re: Think you understand the relationship of torque and powe

Postby jondee86 » Tue Feb 24, 2015 8:54 pm

I prefer to build up to the big one, kind of like this....

An engine makes 200hp at 3000rpm, but the throttle is too small, and power
drops off after 5000rpm so that the engine only makes 200hp at 6000rpm. At
6000rpm does the engine make...
1. Twice the torque that it made at 3000rpm
2. Half the torque that it made at 3000rpm
3. The same torque it made at 3000rpm

After fitting a larger throttle, the engine makes 200hp at 3000rpm and 400hp
at 6000rpm. At 6000rpm does the engine make...
1. Twice the torque that it made at 3000rpm
2. Half the torque that it made at 3000rpm
3. The same torque it made at 3000rpm

Following some adjustments to fuel and ignition timing, the engine makes peak
power of 420hp at 6600rpm. At 6600rpm does the engine make...
1. More torque than it made before at 6000rpm
2. The same torque it made before at 6000rpm
3. Less torque than it made before at 6000rpm
4. The same torque it made before at 3000rpm

Something along these lines :)

Cheers... jondee86
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Re: Think you understand the relationship of torque and powe

Postby Clouds » Wed Feb 25, 2015 7:12 am

Oh, this is probably gonna make me feel dumber than when I read Oldskewltoy's build threads. :lol:

Edit 1: Sitrep. Could not open quiz because the internet where I am is going really slowly. Will try again later.

Edit 2: Status Report. I got one right. :? :oops:
There shouldn't be a day that goes by where you don't learn something new.

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Re: Think you understand the relationship of torque and powe

Postby ae90tuner » Wed Feb 25, 2015 6:00 pm

So would an engine that produces more torque exit a corner faster than a higher strung engine? all else being equal.

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Re: Think you understand the relationship of torque and powe

Postby jondee86 » Wed Feb 25, 2015 7:28 pm

ae90tuner wrote:So would an engine that produces more torque exit a corner faster
than a higher strung engine? all else being equal.

The car that puts most torque to the ground at any particular road
speed, will accelerate more rapidly out of a corner. So you need to
take into account overall gearing (gearbox ratio, diff ratio and tire
size) plus where the engine is on its torque curve at that moment.

As the road speed increases, the engine moves up its torque curve,
and the torque to the ground changes. Where you notice this is a
race between two similar cars with different overall gearing. Off the
line one car will get the jump, but as they are not changing gear at
the same time, the lead may change more than once.

The car geared to hit the limiter right on the finish line will be the
winner if the other car is 2000rpm short of redline. This is why
most serious competitors in any form of racing, will have a
selection of rear end ratios that they can change at the track.

However, to answer your question, if you had two identical cars
with identical engines, except that one had 10ft-lbs of torque more
than the other right across its torque curve, the car with the higher
torque engine would be faster. But as soon as you change anything
in the equation...... refer the long answer above :D

Cheers... jondee86
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Re: Think you understand the relationship of torque and powe

Postby yoshimitsuspeed » Wed Feb 25, 2015 7:41 pm

ae90tuner wrote:So would an engine that produces more torque exit a corner faster than a higher strung engine? all else being equal.


The problem is that people misuse the word torque to mean low end power. This is a huge part of the reason for making this quiz is trying to get people thinking about this terminology properly.

You say an engine that produces more torque but it all depends on where it makes more torque.
People have been using this terminology wrong for decades. There are amazingly capable engine builders who can get 400 hp per liter out of a motor yet still don't use torque and power properly.

This all started a long time ago when manufacturers and others when they couldn't be bothered to show a complete dyno or if they didn't have one available would list peak power and peak torque on a motor.
This is actually handy if you know the RPM of the peak torque because you could then have two datapoints to create a crude dyno graph. Two data points are far from ideal but better than one.
Without the RPM that figure is practically useless. This is similar to the third question in the quiz. Torque is a useless figure until you have an RPM. At that point you can measure how much work it can do. This is called power.
Due to the formula for HP as we measure it in the US HP = Torque x RPM ÷ 5252 torque will always be higher than power below that RPM and lower than power above that RPM.
These two things combined give people the impression that torque = acceleration at lower RPM. After all if you increase peak torque on a dyno graph you will tend to see an increase in the lower RPM because motors tend to make peak torque at a lower RPM than peak power.
The truth is that as you increase torque at that RPM you also increase power at that RPM.
This is why it's inaccurate to say that you will have better low RPM acceleration if you increase torque. If you increase torque at 8000 RPM you will gain power at 8000 RPM and accelerate faster at 8000 RPM.
If you increase torque at 3000 RPM you will increase power at 3000 RPM and will therefore accelerate faster. How fast you can accelerate cannot be determined with torque alone. You need RPM to calculate how much work the motor can do over time. That is power.

The other thing to remember is that cars have transmissions for a reason. What is a transmission? A torque multiplier.
So the motor that produces the most power at the RPM you are exiting the corner will accelerate the fastest out of it.
For a better understanding of this pay attention to question 4 on the quiz and the detailed explanation of that question after the quiz.

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Re: Think you understand the relationship of torque and powe

Postby yoshimitsuspeed » Wed Feb 25, 2015 8:05 pm

jondee86 wrote:
As the road speed increases, the engine moves up its torque curve,
and the torque to the ground changes. Where you notice this is a
race between two similar cars with different overall gearing. Off the
line one car will get the jump, but as they are not changing gear at
the same time, the lead may change more than once.

The car geared to hit the limiter right on the finish line will be the
winner if the other car is 2000rpm short of redline.


There are so many variables in racing that I have stopped using it to try to explain these principals and prefer to stick to more controlled situations.

For example your explanation above isn't universally true.

This stock NA AW11 will be able to do more work/time at 6000 RPM than it will at 7500.
This means that if two cars running this motor were geared to go the same speed but one was at 6000 RPM and the other was at 7000 RPM the car at 6000 RPM would be accelerating slightly faster. More importantly if they are accelerating the car at lower RPM is gaining power and therefore rate of acceleration while the car at 7000 RPM is loosing power and rate of acceleration.
But in racing it doesn't all come down to power. The car at 7000 RPM would be better off downshifting to 6000 RPM in terms of acceleration but they will loose time in the shift so the driver needs to make the judgement call as to whether they will loose less time by shifting or by taking it to the rev limiter.

This is why I find it way more important to pay attention to power.
Like you say what is really important is the amount of torque at the wheels but it would take a lot of math to figure out what section of the torque curve and what gearing would accomplish that.
On the other hand you can look at the power curve and know that at the point of peak power will be where the motor will be able to apply the most energy to acceleration. As long as it's geared to hit that RPM at the speed you are going you will apply the maximum possible torque to the wheels and therefore have the greatest acceleration.

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Re: Think you understand the relationship of torque and powe

Postby oldeskewltoy » Thu Feb 26, 2015 8:19 am

yoshimitsuspeed wrote:
For example your explanation above isn't universally true.



jondee... take it from me.... back away... don't take the bait :lol:
OST Cyl head porting, - viewtopic.php?f=22&t=300

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Re: Think you understand the relationship of torque and powe

Postby yoshimitsuspeed » Thu Feb 26, 2015 11:17 am

oldeskewltoy wrote:
yoshimitsuspeed wrote:
For example your explanation above isn't universally true.



jondee... take it from me.... back away... don't take the bait :lol:


So what did you score?

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Re: Think you understand the relationship of torque and powe

Postby jondee86 » Thu Feb 26, 2015 2:22 pm

oldeskewltoy wrote:jondee... take it from me.... back away... don't take the bait :lol:

Oh, I know that my off the cuff example is not a universal truth :)

I was trying to offer something up that would emphasise the importance
of optimising the power and torque that you have available. My engine is
going to (hopefully) make peak power around 7600rpm and peak torque
around 5400rpm. I call 8000rpm redline and set my fuel cut at 8200rpm.

So with these numbers in mind, hitting the finish at redline would near
enough be using all the potential of the engine. A little bit of over-rev
past peak power is not going to hurt anything like an extra gear change.

Of course, if another engine makes peak torque early and falls over early,
then revving to a high redline while power is falling is a losing strategy.

Cheers... jondee86
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Re: Think you understand the relationship of torque and powe

Postby oldeskewltoy » Thu Feb 26, 2015 4:00 pm

yoshimitsuspeed wrote:
oldeskewltoy wrote:
yoshimitsuspeed wrote:
For example your explanation above isn't universally true.



jondee... take it from me.... back away... don't take the bait :lol:


So what did you score?



score?

I haven't even looked yet... figured I'd see what others thought of them first. Also figured any criticism I made wouldn't be received well, so I've tried to stay away - jondee seemed to have a few... nothing glaring just different frames of mind
OST Cyl head porting, - viewtopic.php?f=22&t=300

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Re: Think you understand the relationship of torque and powe

Postby yoshimitsuspeed » Thu Feb 26, 2015 5:23 pm

oldeskewltoy wrote:
score?

I haven't even looked yet... figured I'd see what others thought of them first. Also figured any criticism I made wouldn't be received well, so I've tried to stay away - jondee seemed to have a few... nothing glaring just different frames of mind


The test has already gotten thumbs up by a number of engineers and everyone who knows what they are talking about seems to have mostly positive things to say about it so criticism doesn't mean much to me at this point.

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Re: Think you understand the relationship of torque and powe

Postby ae90tuner » Thu Feb 26, 2015 7:46 pm

I guess to be more specific i'm talking about an engine that makes 20lb more torque at 3,000-4,000 rpm than one that makes 20lb less. When I say an engine that produce more torque I guess I was assuming how most people identify torque as low end power, and horsepower as high end power, although hp is just torque measurements x rpm. Sure you can be more specific but I think the execution and results are more than enough even IF its not technically correct.

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Re: Think you understand the relationship of torque and powe

Postby jondee86 » Thu Feb 26, 2015 8:23 pm

yoshimitsuspeed wrote:... and everyone who knows what they are talking about seems to have
mostly positive things to say about it...

In some circles this is know as "preaching to the converted" :)

... so criticism doesn't mean much to me at this point.

I had assumed from your going to the trouble of preparing this test, that
you had some positive intention in mind. That you were perhaps trying to
raise an awareness of the relationship between power and torque in the
minds of those who may be struggling with the concepts.

If this is the case, then rather than seeking the approval of your fellow
engineers, maybe you should be seeking feedback from your target audience ?
Identifying the areas in which understanding is lacking should help guide you
in formulating questions that lead to increased understanding. However, if
your goal is to engage in learned debate with industry professionals, then
maybe this is the wrong forum ?

You can ignore this if you want ;)

Cheers... jondee86
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Re: Think you understand the relationship of torque and powe

Postby yoshimitsuspeed » Thu Feb 26, 2015 9:36 pm

ae90tuner wrote:I guess to be more specific i'm talking about an engine that makes 20lb more torque at 3,000-4,000 rpm than one that makes 20lb less. When I say an engine that produce more torque I guess I was assuming how most people identify torque as low end power, and horsepower as high end power, although hp is just torque measurements x rpm. Sure you can be more specific but I think the execution and results are more than enough even IF its not technically correct.


An engine that makes 20 lb ft more torque at say 3500 RPM will do more work than a motor than the motor that makes 20 less. So yes at that RPM it would accelerate out of a corner faster, lift more weight faster, etc.
Much of the point of this is trying to get people to understand it correctly and use proper terminology and understand what those terms really need.
It's not about being specific it's about being correct or incorrect. The problem with saying incorrect is good enough if others understand what you mean is that it will lead others who are trying to learn what is correct to believe that it is. On the other hand a little effort to try to point out what is correct may just influence a few others to see another side and try to point it out to others spreading more knowledge and correct understanding.

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Re: Think you understand the relationship of torque and powe

Postby yoshimitsuspeed » Thu Feb 26, 2015 9:48 pm

jondee86 wrote:
yoshimitsuspeed wrote:... and everyone who knows what they are talking about seems to have
mostly positive things to say about it...

In some circles this is know as "preaching to the converted" :)

... so criticism doesn't mean much to me at this point.

I had assumed from your going to the trouble of preparing this test, that
you had some positive intention in mind. That you were perhaps trying to
raise an awareness of the relationship between power and torque in the
minds of those who may be struggling with the concepts.

If this is the case, then rather than seeking the approval of your fellow
engineers, maybe you should be seeking feedback from your target audience ?
Identifying the areas in which understanding is lacking should help guide you
in formulating questions that lead to increased understanding. However, if
your goal is to engage in learned debate with industry professionals, then
maybe this is the wrong forum ?

You can ignore this if you want ;)

Cheers... jondee86


It does have a positive intention in mind but there are still going to be those who are too closed off or committed to their beliefs to be open to other suggestions. I am not trying to change their mind. I am hoping to catch those people on the fence or the ones who have this strange feeling that what they have been taught just doesn't seem quite right.
The test is designed to get people thinking about these things in a different light and based around the simple formulas that makes it all work.
The input I was looking for from engineers and other technically minded people was on it's technical accuracy, not it's ability to educate. I have tried dozens of different angles trying to educate people on this subject and it never ends well unless they are the ones approaching you with curiosity.
This quiz is designed to test peoples technical knowledge on the subject. If they do poorly it's up to them to decide they want to learn about it. This is why there are links to educational information at the end of the test. At the very least maybe it will make them think twice about being qualified to argue with others about the subject.

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