How do you increase Torque?

[Alastor]

I pose to you that a steam train has 5000Nm of torque but only 300kW. It can pull a 20 carriage train from a standing start quite easily. Put your 300kW car with 500Nm in front and try to pull it. You wont move it easily.

But if you mate a 10:1 transmission to the engine that makes 500Nm of torque, the output shaft of the transmission could generate 5000Nm at the same engine speed as the first engine.

Torque is all important at the lower rev ranges for acceleration while horsepower is low. You may have 300kW on tap, but at what RPM. If it is at 6,000rpm the power at 3,000rpm may be 150kW. So if the torque is higher at lower RPM then not only is your power going to be higher at this point but it will accelerate quicker to 6,000rpm. What I am trying to say is that if you provide higher torque at a lower RPM then your power curve will rise faster and be more flat through the midrange making it accelerate stronger through the rev range. So peak power is not as important as a wide flat power range provided by a good torque curve if you want the fastest time between A and B.

Similarly, if you are cruising in a high gear and you approach a hill. The lower torque engine will have to gear down to increase horsepower before the high torque engine has to. It's all about driveability and efficiency. A flat torque curve is most desirable in production cars as it gives a smooth even acceleration. People who like to drive harder may like the power peak feel. The heavier the vehicle, the more torque is desirable.

When you are talking about the torque curve you are talking about torque as a function of engine speed, which makes it equally as useful as the power curve. Both curves are useful, one is really not better than other.

However, when the curves are unknown knowing peak power alone is more useful than knowing peak torque alone.

[revetec]

But if you mate a 10:1 transmission to the engine that makes 500Nm of torque, the output shaft of the transmission could generate 5000Nm at the same engine speed as the first engine.

But then it would have no vehicle top speed.

When you are talking about the torque curve you are talking about torque as a function of engine speed, which makes it equally as useful as the power curve. Both curves are useful, one is really not better than other.

However, when the curves are unknown knowing peak power alone is more useful than knowing peak torque alone.

Power is calculated on a torque measurement, Not the other way around. Ask any dyno manufacturer. Dynos only measure torque. Power is then calculated from that reading and RPM.
A leading Japanese car manufacturer told me that torque was all important as when you have good torque, you automatically make good power economically. (Not the other way around)

[Alastor]

But then it would have no vehicle top speed.

The transmission output shaft would be spinning at the same speed as the first engine drive shaft. Since the first engine didn't require top speed, it shouldn't be required of the second engine for the same application.

Power is calculated on a torque measurement, Not the other way around. Ask any dyno manufacturer. Dynos only measure torque. Power is then calculated from that reading and RPM.

I think it depends on the type of dynamometer, but then again I am no dyno manufacture. Nevertheless, as far as I know torque is not typically measured directly either. The force is measured at a known moment arm, and the torque is calculated from there.

Not that it matters, just because the power is measured indirectly doesn’t invalidate it’s usefulness. It is the definition of power that is important not how it is measured.

[hightower99]

The torque of an engine is measured directly in a dyno. Basically the engine is forced to rotate a lever arm and at the end of the lever arm is a load sensor that measures the torque coming from the engine. To get the absolute torque rating at any RPM for any engine then the loading on the lever arm should be enough to hold the engine stable at the target RPM at WOT.

Now lets think about this: The torque of the engine is measured in full only when the system is standing still (and the RPM is totally stable). Now if you set a target RPM for every 100rpm in the operating range you could put together a nice torque curve. Then power is easily calculated. However this way of measuring engine output takes a long time and needs adjustable loads and a way to dissipate all the heat generated.


Now most dynos used for cars do not hold the engine at a stable RPM to measure torque. Instead most automotive dynos have a set work load and the engine is forced to do that work at WOT. The faster it can do the work (normally accelerating a rotating weight) the more power the engine is putting out. So in actual fact most dynos out there measure power directly.
A big hint is the fact that many dyno charts use speed instead of RPM to show the power curve. You cannot calculate the torque needed to accelerate to any speed but there is an easy to calculate minimum power requirement to accelerate to any speed. The computer normally does this simple calculation coupled with several adjusting factors to decide the actual power output of the engine.

I pose to you that a steam train has 5000Nm of torque but only 300kW. It can pull a 20 carriage train from a standing start quite easily. Put your 300kW car with 500Nm in front and try to pull it. You wont move it easily.

You would be wrong in every way. If both systems are allowed to maintain their respective outputs of 300kW and transfer that power 100% then you will find that the car will accelerate faster (because it is lugging the 20 carriage train and the 1000-2000kg of car in stead of the 10000-60000kg of engine train. In real life what helps the train is the immense weight of itself creating massive traction which allows it to output the 300kW at low speeds. Nothing to do with it's torque.

Torque is all important at the lower rev ranges for acceleration while horsepower is low. You may have 300kW on tap, but at what RPM. If it is at 6,000rpm the power at 3,000rpm may be 150kW. So if the torque is higher at lower RPM then not only is your power going to be higher at this point but it will accelerate quicker to 6,000rpm. What I am trying to say is that if you provide higher torque at a lower RPM then your power curve will rise faster and be more flat through the midrange making it accelerate stronger through the rev range. So peak power is not as important as a wide flat power range provided by a good torque curve if you want the fastest time between A and B.

I never said peak power is the be all end all. The power curve is. Torque on it's own means nothing however I agree that you should try to tune an engine to have a flat torque curve (more pratically a slightly rising one) as this will get the best power curve, which is what does all the wok. You are perpetuating the myth that at low rpm, torque mystically becomes more important than power. This is totally wrong. Higher torque at lower rpm is only beneficial because that means that you are making more power at low rpm. The power curve is everything. Instead of claiming that you engines make such great low rpm torque you will impress people much more if you claim that you can generate much more power at low rpm.

Similarly, if you are cruising in a high gear and you approach a hill. The lower torque engine will have to gear down to increase horsepower before the high torque engine has to. It's all about driveability and efficiency. A flat torque curve is most desirable in production cars as it gives a smooth even acceleration. People who like to drive harder may like the power peak feel. The heavier the vehicle, the more torque is desirable.

I partially agree with you. I would totally agree if you replaced the word torque with power. It is the power curve that dictates when you have to shift down a gear to continue up the hill. The heavier the vehicle the more you have to concentrate on creating the proper power curve.

[henk4]

You are perpetuating the myth that at low rpm, torque mystically becomes more important than power. This is totally wrong. Higher torque at lower rpm is only beneficial because that means that you are making more power at low rpm.

Compare the torque and power curves of diesel and petrol engines and then you will understand the all importance of low revs and high torque.

[henk4]

In real life what helps the train is the immense weight of itself creating massive traction which allows it to output the 300kW at low speeds.

on your way to the perpetuum mobile aren't you?

[Alastor]

The torque of an engine is measured directly in a dyno. Basically the engine is forced to rotate a lever arm and at the end of the lever arm is a load sensor that measures the torque coming from the engine.

If you are measuring force at a known moment arm you are measuring force directly and torque indirectly.

Even then I used a simple dynomometer is school that used a spring loaded scale to measure force. So in that case force wasn't even measured directly, it was actually the displacement of the spring that was being measured.

So to say power is some how not useful because it is 'calculated' from torque is silly, because the same line of reasoning would invalid torque and maybe even force.

[revetec]

You would be wrong in every way. If both systems are allowed to maintain their respective outputs of 300kW and transfer that power 100% then you will find that the car will accelerate faster (because it is lugging the 20 carriage train and the 1000-2000kg of car in stead of the 10000-60000kg of engine train. In real life what helps the train is the immense weight of itself creating massive traction which allows it to output the 300kW at low speeds. Nothing to do with it's torque.

I'm sorry but you are wrong. A steam engine can provide 5000Nm of torque from 0 RPM. This allows it to provide a huge lever to start moving the train. This is why there are diesel electric trains and not diesel trains. The electric drive can provide huge force from 0 RPM to move the mass. A transmission would have to have a ridiculously high ratio to do the same thing.

This does relate to a normal car. The higher the torque, the more force you have to provide a good acceleration. Of course the better the torque the more work can be done and this is power.

I'll give another example. An F1 car has very high power due to the high achievable RPM. What do they do to move the mass of the car from a standing start? They have to Rev the engine to about 10,000rpm and dump the clutch to even get the car rolling. I pose to you that this car may have over 100kW at 3,000rpm? Well and truly enough to get the car off the mark as a production car can move that mass with the same power. What happens? The engine bogs and dies if this is done. Another factor is also the way the breathing is setup, but there is still enough power to do it.

Now look at diesels. Lower power but higher torque. They pull heavy loads off the mark utilizing more torque.

Power is a product between Torque and RPM. They cannot be separated but the fact of the matter is that torque is what turns your shaft and power is how many times a minute you can rotate it at that torque.

A quote from REVSEARCH:
On modern day dynamometers horsepower is a calculated value. It's important to remember the dyno measures torque and rpm and then from these calculates horsepower. On the dyno it takes more water flow to the water brake to increase the load on the engine being tested. As the test engine's torque rises more water flow is needed. As the test engine's torque drops less water flow is needed. The dyno's water brake does not respond to Horsepower. Major adjustments to water flow are needed as an engine crosses its torque peak but none are needed as it crosses its horsepower peak. In other words the water flow to the brake during a dyno test follows the engines torque curve and not its horsepower curve. Torque is what twists the tire, prop, or pump. Horsepower helps us understand an amount or quantity of torque. (Torque + time and distance)



One other example I could give is that you have a car standing still on an incline and you are slipping the clutch to hold it there but the wheels are not turning. The torque at the wheels is holding the car there, but with no rotation the horsepower would be Zero at the wheels. As it rotates once the load is pulled a slight distance giving a very small horsepower even though a huge load may have been moved by the torque applied. The more horsepower required, the more fuel usage.

I think that last example was the best explanation.

BTW: I have my own Dyno Dynamics engine dyno right here. It is of an Eddy current variety and has a electronic torque load sensor.

[Slicks]

hightower99, sorry but it is torque that moves the car.
If your car is making 300ft.lbs of torque at 2000RPMs, and making the same 300ft.lbs of torque at 4000RPMs, the car will not be accelerating any harder at 4000RPMs although hp is doubled. Your cars acceleration follows the torque curve exactly.

[Alastor]

hightower99, sorry but it is torque that moves the car.
If your car is making 300ft.lbs of torque at 2000RPMs, and making the same 300ft.lbs of torque at 4000RPMs, the car will not be accelerating any harder at 4000RPMs although hp is doubled. Your cars acceleration follows the torque curve exactly.

All else being equal, the second car would have the same acceleration at twice the road speed. If you measured the acceleration at the same road speed the second car would have twice the acceleration. So at any road speed the second car will be faster.

[hightower99]

Compare the torque and power curves of diesel and petrol engines and then you will understand the all importance of low revs and high torque.

No actually when I look at diesel engine power curves I can appreciate the massive power they produce from low rpm. I love diesel engines, for there size they trump petrol engines for power up to about 4500-5000rpm then petrol really takes over.

on your way to the perpetuum mobile aren't you?

I have no idea what you are on about. My point was that the trains weight helped it get the traction needed to put the 300kW into the carriages behind it. If a car with 300kW tried to pull the carriages it would juist spin it's wheels due to much lower traction.

I'm sorry but you are wrong. A steam engine can provide 5000Nm of torque from 0 RPM. This allows it to provide a huge lever to start moving the train. This is why there are diesel electric trains and not diesel trains. The electric drive can provide huge force from 0 RPM to move the mass. A transmission would have to have a ridiculously high ratio to do the same thing.

5000Nm at 0rpm can't do any work it can only hold things still. As soon as you have 1rpm (or even 0.0001rpm) it is the power that is doing work. Having the high torque means you have good power even at low rpm. I am not saying that torque should be disregarded at all, simply that you shouldn't compare engines on peak torque values. The power curve is the only thing a tuner should be interested in because he would also indirectly be interested in the torque curve. See what I mean you can't do that backwards, you can't focus solely on torque because that excludes power (which is the important bit). Also the main reason why they have diesel electrics instead of pure diesels is because of the drivetrain needed to get mechanical power from the massive engine to all 8 wheels of the train would be overly complex and incurr rather large losses.

This does relate to a normal car. The higher the torque, the more force you have to provide a good acceleration. Of course the better the torque the more work can be done and this is power.

slightly wrong, more right. The more power you have the more work you can do the faster you can acccelerate. more torque doesn't mean you can do more work.

I'll give another example. An F1 car has very high power due to the high achievable RPM. What do they do to move the mass of the car from a standing start? They have to Rev the engine to about 10,000rpm and dump the clutch to even get the car rolling. I pose to you that this car may have over 100kW at 3,000rpm? Well and truly enough to get the car off the mark as a production car can move that mass with the same power. What happens? The engine bogs and dies if this is done. Another factor is also the way the breathing is setup, but there is still enough power to do it.

You are again making an example that leaves out several important factors. Firstly a F1 engine doesn't make 100kW at 3000rpm niether do they need to take off at 10 000rpm. Next the reason why an F1 engine is prone to stalling compared to a normal car engine of the same size, has alot more to do with the wraithlike inertial weight of the F1 engine internals (including the super-duper light fly wheel) compared to the heavy internals and heavy fly wheel of normal cars and the on/off high clamp force clutch that is used. But you would have trouble getting a F1 car to take off gently with only, say 2000rpm. The reason being that the design of the engine produces very little power at that rpm.

Now look at diesels. Lower power but higher torque. They pull heavy loads off the mark utilizing more torque.

Wrong they utilize more power at low rpm to pull heavy loads while burning less fuel due to higher thermal efficiency.

Power is a product between Torque and RPM. They cannot be separated but the fact of the matter is that torque is what turns your shaft and power is how many times a minute you can rotate it at that torque.

Correct power and torque can't be seperated but you can compare engines on there power curve, and not neccessarily on there torque curve and certainly not peak torque values. Power is what rotates the shaft, torque is an abstract value of force applied per shaft rotation. Do you really think that an engine that produces 500hp at 2000rpm can do any more work then an engine that makes 500hp at 6000rpm?

hightower99, sorry but it is torque that moves the car.
If your car is making 300ft.lbs of torque at 2000RPMs, and making the same 300ft.lbs of torque at 4000RPMs, the car will not be accelerating any harder at 4000RPMs although hp is doubled. Your cars acceleration follows the torque curve exactly.

Wrong, You obviously are mislead or not very intelligent because you are blatantly disregarding the fact that the kinetic energy required is equal to half the mass of the object times the square of the objects velocity. that means that if you double the speed, you need to add 4 times the energy. Power is energy per unit time so to continue a given rate of acceleration at twice the speed you would need to make 4 times the power. Since you only doubled power you would cut the acceleration in half even though your torque remained constant. I hope everyone else here can see this obvious flaw.

Acceleration follows the power curve exactly.

All else being equal, the second car would have the same acceleration at twice the road speed. If you measured the acceleration at the same road speed the second car would have twice the acceleration. So at any road speed the second car will be faster.

wrong the second car would accelerate at half the rate of the first one at twice the speed. Otherwise you are correct with twice the power it would accelerate faster at any given speed than the first car.

[henk4]

can you explain in technical terms why diesel powered cars have better in gear acceleration than petrol powered cars? (compare for instance a Golf GTI which comes either with a petrol engine or with a TDi, both about 170 BHP). In my humble opinion that is because the torque plays the decisive role...hence I prefer to look at torque curves rather than a power curves, because it tells me much more about the driveability of a car.

[henk4]

I have no idea what you are on about. My point was that the trains weight helped it get the traction needed to put the 300kW into the carriages behind it. If a car with 300kW tried to pull the carriages it would juist spin it's wheels due to much lower traction.

but the weight has to be put in motion first. So this is not about mechanics but about adhesion. (If there are autumn leaves on the railway track, the train will also not move....)

[Alastor]

wrong the second car would accelerate at half the rate of the first one at twice the speed. Otherwise you are correct with twice the power it would accelerate faster at any given speed than the first car.

Instantaneous acceleration is directly proportional to the torque at a given engine speed, correct?

So for the first car it creates some acceleration at an engine speed of 2000 RPM. If you double the engine speed, keeping the transmission, tires size, mass, etc the same, you double the road speed. So the second car makes the same torque at twice the engine speed (or road speed if you prefer) but experiences the same instantaneous acceleration.

I understand were you are coming from with the half acceleration, if you are thinking about kinetic energy. However, for that to be applicable don't you need an initial and final velocity as a apposed to an instantaneous measure?

[hightower99]

can you explain in technical terms why diesel powered cars have better in gear acceleration than petrol powered cars? (compare for instance a Golf GTI which comes either with a petrol engine or with a TDi, both about 170 BHP). In my humble opinion that is because the torque plays the decisive role...hence I prefer to look at torque curves rather than a power curves, because it tells me much more about the driveability of a car.

Yes indeed I can:

If the diesel accelerates faster then it produces more power at the low revs then the petrol version of the car. The only reliable graphs I could find compare '97 passats 1.8T against 1.9TDI and I can tell you that the TDI would pull harder in through the gears because it makes 10-15hp more up to 4000rpm. This means that it will pull noticably harder for 2000-2500rpm then change gears at 4500rpm. The petrol engine is behind until 4000rpm where it starts making more power.

So in the end the pertrol will win because it can hold on to the gear longer and put more power (as much as 35hp more) into it for the last 2000-2200rpm after 4000rpm.

Torque curves on there own do not tell you about the drivablity at all. The power curve tells you exactly how drivable the engine is.

but the weight has to be put in motion first. So this is not about mechanics but about adhesion. (If there are autumn leaves on the railway track, the train will also not move....)

I don't know what you mean. The weight gives the train much more traction standing still as well as when it is moving. I hope you realise that friction is an important consideration in almost all mechanical systems...

BTW autumn leaves don't stop trains. There is soo much weight on the miniscule contact patches on trains that they can smash nickels and dimes flat against the steel rails (both are relatively tough copper/nickel alloys) and turn granit stones into powder, not many cars can do that.