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Here is a question and response on a question of Torque at Ask.Cars.com:
Q:I know horsepower relates to how powerful a car is versus another, but what is torque? Why is it different than horsepower? Should I consider torque numbers when researching new cars? Is it more important for different types of vehicles?
A: As you know, an engine’s output is rated in horsepower and torque. Torque is pulling power, and it’s best demonstrated as the grunt that gets you moving, while horsepower is what keeps you going. Without sounding like your high-school physics teacher, torque is the twisting force created in an engine by rotating parts; horsepower is the measurement of how fast torque is being used. Horsepower and torque work hand-in-hand, as horsepower is calculated from torque. For the average buyer, torque shouldn’t be a deciding factor unless you know you’ll be towing or hauling heavy loads. And that’s where high-torque vehicles will thrive, driving while towing a trailer or maxing out cargo capacity. It will be easier to accelerate and sustain speed with a high-torque car in any situation, but especially with heavy loads. High-performance cars can also produce gobs of torque that greatly aid in acceleration. That feeling of your eyeballs being sucked into the back of your head in a fast car during heavy right-foot pounding is an example of excessive torque.
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Another explanation of torque is the use of a transmission.
If you are driving and approach a very steep gradiant and put your foot down. The gradient is so steep that your maximum power cannot maintain speed and your speed drops. You downshift to a lower gear and then are able to accelerate. Your speed is less, but you can maintain that speed at the same RPM and load of the engine that you were previously at.
So what has happened? Power is the same, the same work is being done. A transmission takes that power and changes the RPM and torque values ie. Lower RPM output, and higher torque. Nothing has changed in Power.
A transmission is a torque multiplier, not a power multiplier.
Given a particular given top power rating, if an engine produces higher torque at a lower RPM then it reduces the need to gear down. Extra torque also reduces the throttle opening required to overcome the extra load given a certain speed. Lower throttle opening reduces engine breathing which reduces fuel consumption.
Here is a dyno graph of our X4v2 engine which provides this...
[IMG]http://www.revetec.com/images/dev_dynograph_x4v2.jpg[/IMG]
Note: We have 90% of peak torque at 1,300RPM, Peak torque at 3,000RPM
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This engine provides [B]almost uniform acceleration[/B] from 1,300RPM to 3,500RPM (+/-10%). [B]Power ranges from 25kW to 68kW[/B]
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[quote=revetec]Well start a topic on the BMW Turbosteamer then and I will be active in it.[/quote] Done :p Here is the [ame="http://www.ultimatecarpage.com/forum/showthread.php?t=42083"]thread.[/ame]
BTW the answer from the ask.cars.com article is exactly the type of incorrect information that I positively loath!
The second sentence: [quote=ask.cars.com answer]Torque is pulling power, and it’s best demonstrated as the grunt that gets you moving, while horsepower is what keeps you going.[/quote]is complete non-sense! The anecdotal response that implies that engine torque is the deciding factor for determining towing capacity is absolute rubbish! The whole answer is utterly incorrect in so many ways that it isn't even close to funny. The answer was apparently given by one Joe Bruzek who AFAIK is only an expert journalist, and not an actual engineering expert in any way or form.
[quote=henk4]If they are that irrelevant, why would manufacturers quote them in the first place? Just to pamper what you call illusions?[/quote]Unfortunately just because a company talks about it doesn't actually mean that it is important in any way. You will notice that power is shown much more often than torque values. So by your own logic power must be more important :rolleyes: Also you should give yourself more credit. Having graduated as an economist and having more than 30 years of life experience after that, you are more than able to read the article and share your interpretation.
Alastor: Thank you for your effort. I have made another thread for discussing the turbosteamer if you are interested in continuing.
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In vehicle testing, the engine did not provide 175% increase in acceleration at 3,500RPM as it did at 1,200RPM, it was almost constant. The vehicle accelerated at the same rate as the torque curve. No doubt that the power increased, which created more speed and more work done, but it's the torque curve which determined the acceleration rate.
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Hightower99: Power and Torque will always be debated, but they have different characteristics in operation. It depends on your driving style, load of your vehicle, operational conditions, and whether or not you are looking for performance or economy.
Like I said, they are as important as each other.
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[quote=revetec;945311]So what has happened? Power is the same, the same work is being done. A transmission takes that power and changes the RPM and torque values ie. Lower RPM output, and higher torque. Nothing has changed in Power.
A transmission is a torque multiplier, not a power multiplier.
[/quote]
This is exactly why torque at the engine is irrelevant. When I talk, and I am assuming this applies to hightower99 as well, is that torque at the wheel is what matters.
Torque at the engine is irrelevant because it can be multiplied as much as is desired using a transmission. So a small engine producing a small amount of torque can be geared to produce huge amounts of torque via a transmission at the 'wheel'.
However, power must always be conserved and thus is a more useful measure.
I think much of your augment has been for the value of understanding torque at the engine. Which certainly has merits in terms of IC engine design, but once you start talking about vehicle performance it become less important because of the transmission.
[quote=revetec]The vehicle accelerated at the same rate as the torque curve. No doubt that the power increased, which created more speed and more work done, but it's the torque curve which determined the acceleration rate.[/quote]
This should be always true when using fixed gear ratios because the torque at the wheels is directly proportional to the torque at the engine. However, when you 'de-couple' the engine and wheel so that you can use a varying gear ratio (as opposed to a fixed gear ratio) the value of power becomes much more clear. Now instead of talking about [b]torque&power[/b] and [b]RPM[/b] we are talking about [b]torque&power[/b] and [b]road speed[/b]. Once you put things in terms of road speed it turns the 'traditional' view of torque and power upside down.
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[quote=revetec]If you are driving and approach a very steep gradiant and put your foot down. The gradient is so steep that your maximum power cannot maintain speed and your speed drops.[/quote]So far so good...
[quote=revetec]You downshift to a lower gear and then are able to accelerate. Your speed is less, but you can maintain that speed at the same RPM and load of the engine that you were previously at.[/quote]This is somewhat confusing. If you are able to accelerate then you would have been able to maintain your previous speed in the previous gear, but your example said that the maximum power was not enough for that particular speed. In which case you have slowed down and changed gears so that maximum power now occurs at a slower speed.
[quote=revetec]So what has happened? Power is the same,[/quote]Yes it is. It is the maximum that the engine can produce (peak power).
[quote=revetec]the same work is being done.[/quote]Yes but the rate of work has changed. You said that the car is now moving more slowly up the gradient hence a lower rate of work. Guess what the term for rate of work is???
[quote=revetec]Given a particular given top power rating, if an engine produces higher torque at a lower RPM then it reduces the need to gear down.[/quote]Only because it is making more power at the lower RPM.
[quote=revetec]This engine provides almost uniform acceleration from 1,300RPM to 3,500RPM (+/-10%). Power ranges from 25kW to 68kW[/quote]Look at it like this: From 1300RPM to 3500RPM is a factor 2.7 difference in speed for any given gear ratio. Guess what, the power increases by a factor 2.7 as well...
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Also in engine development and testing we don't use Inertia Dynamometers, as Inertia dynos work properly under load only. It will not calculate your horsepower while holding steady at a fixed RPM. The barrels of an Inertia Dynamometer are spun as the vehicle accelerates, and the time that it takes to go from a set range of speeds determines the horsepower of the vehicle.
Because the hydraulic dyno has the ability to provide variable loads, it is able to provide a closer to "real-world" atmosphere for the vehicle than the inertial style dyno. The hydraulic dyno can also, as a result of its braking system, allow a vehicle to stay at a fixed RPM and still accurately measure the torque. This is critical for fuel and ignition tuning and fuel consumption measurement.
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[quote=Alastor;945317]This is exactly why torque at the engine is irrelevant. When I talk, and I am assuming this applies to hightower99 as well, is that torque at the wheel is what matters. [/quote]
You need torque at the flywheel so it can be applied at the rear wheels!
[quote=Alastor;945317]Torque at the engine is irrelevant because it can be multiplied as much as is desired using a transmission. So a small engine producing a small amount of torque can be geared to produce huge amounts of torque via a transmission at the 'wheel'. [/quote]
You need torque in the first place to multiply it? If you multiply it too much, you don't have speed.
[quote=Alastor;945317]I think much of your augment has been for the value of understanding torque at the engine. Which certainly has merits in terms of IC engine design, but once you start talking about vehicle performance it become less important because of the transmission.[/quote]
It really depends how fast you want to go. A tractor has low power, high ratio gearing providing high torque, but has a low top speed. So it does matter. If you can provide higher torque, you don't have to use such high ratio gearing, so provides higher speed.
[quote=Alastor;945317]This should be always true when using fixed gear ratios because the torque at the wheels is directly proportional to the torque at the engine. However, when you 'de-couple' the engine and wheel so that you can use a varying gear ratio (as opposed to a fixed gear ratio) the value of power becomes much more clear. [/quote]
The torque curve is the same at the flywheel, just multiplied at the wheels.
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[quote=revetec;945316]Hightower99: Power and Torque will always be debated, but they have different characteristics in operation. It depends on your driving style, load of your vehicle, operational conditions, and whether or not you are looking for performance or economy.[/quote]No... there is really no debate about what torque or power is.
The discussion is about how each effects a vehicle. All properly educated engineers I have ever talked to (not nearly enough IMO) have never had to have this discussion. They simply see it in the same way, and that way happens to be the way I see it as well. I only ever encounter this apparent "debate" when talking to laymen or people who just haven't had any proper physics education. This is why I find it frustrating that I should have this debate with you. I thought you had a university engineering degree?
All of the characteristics you mentioned are contingent on engine power output.
BTW: Alastor I completely agree with what you write. It is all about torque at the wheels which is determined by power and the particular road speed.
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[quote=hightower99;945318]Only because it is making more power at the lower RPM.[/quote]
[B]No its not, it's making more torque at the lower RPM.[/B] You know dropping the RPM reduces power (unless you were already over peak Power RPM)
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[quote=revetec;945320]You need torque at the flywheel so it can be applied at the rear wheels![/quote]Yes of course you do but what is important is the power which determines how much you can multiply it for any given speed. Do some simple math if you don't believe me.
[quote=revetec]You need torque in the first place to multiply it? If you multiply it too much, you don't have speed.[/quote]Exactly and the ratio of torque to speed is determined by power!!!
[quote=revetec]It really depends how fast you want to go. A tractor has low power, high ratio gearing providing high torque, but has a low top speed. So it does matter. If you can provide higher torque, you don't have to use such high ratio gearing, so provides higher speed.[/quote]Again the ratio of torque to speed is determined by power. The more power the more torque you can make at any given speed.
[quote=revetec]No its not, it's making more torque at the lower RPM.[/quote]If it is making more torque then it is making more power at that given RPM. More Torque = More Power.
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[quote=hightower99;945321]The discussion is about how each effects a vehicle. All properly educated engineers I have ever talked to (not nearly enough IMO) have never had to have this discussion. They simply see it in the same way, and that way happens to be the way I see it as well. I only ever encounter this apparent "debate" when talking to laymen or people who just haven't had any proper physics education. at the wheels which is determined by power and the particular road speed.[/quote]
Go and build yourself an F1 engine with high kW and no torque down low. Stick it in a heavy vehicle. See if you can drive it, and see how economical it is to drive.
F1 engines have heaps of kW and are lightweight. So why do they have problems taking off from a standing start, when my car which is twice as heavy does it with ease and using a fraction of the power? Answer: Torque!
Welcome to the real world!
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[quote=revetec;945324]Go and build yourself an F1 engine with high kW and no torque down low. Stick it in a heavy vehicle. See if you can drive it, and see how economical it is to drive.[/quote]If it has more power than the given truck engine and proper gearing it will outperform the original truck. It will use significantly more fuel as F1 engines aren't that efficient being designed for maximum specific power as opposed to efficiency. On the same token why don't you take a high torque truck engine and put it in a lightweight car. Shouldn't it out accelerate any equivalently powered small petrol engine?
[quote=revetec]F1 engines have heaps of kW and are lightweight. So why do they have problems taking off from a standing start, when my car which is twice as heavy does it with ease and using a fraction of the power? Answer: Torque![/quote]No you got this completely wrong. 1st gear in a F1 car is significantly higher than first gear in your heavy car. An F1 car has no trouble starting if you give it the beans but you end up leaving massive black stripes all over the road. The problem is easing away gracefully. This is hard to do in an F1 car because the clutches are very on/off in their operation, the first gear is much taller (think starting in 3rd in your car) and finally the engines have such little inertia due to the ridiculously light weight that there is no "wiggle room" when engaging the clutch. Either the engine is revving high enough and making enough power to move, or it isn't. Their is very little inertia to "save" you if you get it wrong. Add on top of this the fact that F1 engines are very free revving and very difficult to control and it is easy to see why it would be hard to start.
BTW: Welcome to the truly accurate real world :p