backpressure

[UncleBob]

Originally Posted by Moppie

Is that a royal "we"?
Because I have blue telephone box in the garage that can get around a few time related issues.

let me guess....to use this box requires hooking up electrodes to your scrodum sack...?

[2.2 Straight six]

Originally Posted by Moppie

Is that a royal "we"?
Because I have blue telephone box in the garage that can get around a few time related issues.

if you're reffering to Dr. Who, it wasn't a telephone box, it was a police call box.

British patriotism strikes again...

[Steel]

Originally Posted by UncleBob

torque is a really handy measurement in a plane of existance without time.

Since we don't exist in such a plane.....

?? If i'm trying to turn a wrench on a stuck bolt but it's not going anywhere, im still exerting torque on the bolt.
Just the same, you can only measure the torque produced on a dyno, the horsepower is then derived (and only if the computer knows the speed of the engine!)

[curtis73]

Actually many dynos measure HP and calculate TQ. Many chassis dynos measure the amount of time and speed at which the engine is capable of accelerating the dyno's brake which can be extrapolated to HP.

HP (although mathematically linked to torque) is its own thing. It can be felt if you've ever driven an older porsche. The 2.0L engine makes about 200 lb-ft at 3000 rpms and 200 hp at 6000 rpms. Trust me, the 200 hp puts you back in your seat more than the 200 lb-ft does. Although its a tough concept to grasp, HP is its own force, not just a mathematical derivative of torque.

[UncleBob]

Originally Posted by Steel

?? If i'm trying to turn a wrench on a stuck bolt but it's not going anywhere, im still exerting torque on the bolt.
Just the same, you can only measure the torque produced on a dyno, the horsepower is then derived (and only if the computer knows the speed of the engine!)

a torque wrench isn't a good example. No work is being done with a torque wrench.

When work is wanted (moving something from A to B) time is a factor. Not much work gets done if you apply torque to object and it doesn't move with that amount of torque. Thats called infinity

[UncleBob]

Originally Posted by curtis73

Actually many dynos measure HP and calculate TQ. Many chassis dynos measure the amount of time and speed at which the engine is capable of accelerating the dyno's brake which can be extrapolated to HP.

HP (although mathematically linked to torque) is its own thing. It can be felt if you've ever driven an older porsche. The 2.0L engine makes about 200 lb-ft at 3000 rpms and 200 hp at 6000 rpms. Trust me, the 200 hp puts you back in your seat more than the 200 lb-ft does. Although its a tough concept to grasp, HP is its own force, not just a mathematical derivative of torque.

any vehicle that is high revving will show how true this is. Modern 600cc sport bikes only make 40 ft/lb's. On paper, they look quite pathetic. But at 15K RPM's, that 40 ft/lb's is making over 100hp. The bike is "gutless" (even though it has a fairly flat torque curve) until you get it over 10K RPM's.

[Alastor187]

Originally Posted by UncleBob

a torque wrench isn't a good example. No work is being done with a torque wrench.

When work is wanted (moving something from A to B) time is a factor. Not much work gets done if you apply torque to object and it doesn't move with that amount of torque. Thats called infinity

Actually it is a good example…

It is a good example how torque is not equal to work.

Torque is more akin to force, even if it is not a force in the true sense. There is only work done when there is torque and revolutions. Power comes into play when there is torque and revolutions per unit time.

As well, if you move something from point A to B then you have done work. If you want to know how fast the work is done, then power is of concern.

[UncleBob]

Originally Posted by Alastor187

Torque is more akin to force, even if it is not a force in the true sense. There is only work done when there is torque and revolutions. Power comes into play when there is torque and revolutions per unit time.

As well, if you move something from point A to B then you have done work. If you want to know how fast the work is done, then power is of concern.

If there is work, then there is time. You may or may not be concerned with the time factor, but its always there.

If you are not concerned about the time, then you aren't concerned with the power. They are directly related to each other. Since torque, when involved in a rotational device, is so easily increased or decreased through gear multiplication, there is no limitation to how much torque you create for such a device. You can easily make 1,000,000 ft/lb's of rear wheel torque on any vehicle, but it won't be going anywhere quickly.

As soon as something revolves, there is a time table if you so desire to use it for anything. Since work is usually time sensitive, its more than a minor data point.

[Steel]

Ah, i think we are agreeing with each other but in different ways... again.

[UncleBob]

Originally Posted by Steel

Just the same, you can only measure the torque produced on a dyno, the horsepower is then derived (and only if the computer knows the speed of the engine!)

yah, I'm bored, I wanted to go back to this

No dyno knows what torque an engine is producing until you tell the computer what RPM the engine is at.

All dyno's involved measuring energy. For a drum inertia dyno, all the machine knows is the mass of the drum. When you turn the drum, it calculates the acceleration of the mass OVER TIME and calculates the amount of work being done.

In other words, it first finds the energy being applied to the drum, you could say that its deriving this from the rear wheel torque (torque to the drum shaft) and then finding the energy level, but it can't calculate that until it has the TIME factor.

So the order of calculations: First find the amount of energy, acceleration of mass over time, which is then converted to HP, and THEN...assuming you have an RPM lead to the engine, you can calculate the torque of the engine.

If you have no RPM pickup, then the engines torque is unknown. But the HP is.

[KiwiBacon]

Originally Posted by curtis73

Actually many dynos measure HP and calculate TQ. Many chassis dynos measure the amount of time and speed at which the engine is capable of accelerating the dyno's brake which can be extrapolated to HP.

HP (although mathematically linked to torque) is its own thing. It can be felt if you've ever driven an older porsche. The 2.0L engine makes about 200 lb-ft at 3000 rpms and 200 hp at 6000 rpms. Trust me, the 200 hp puts you back in your seat more than the 200 lb-ft does. Although its a tough concept to grasp, HP is its own force, not just a mathematical derivative of torque.

You have that backwards.

Dyno's measure the reaction torque and the rotating speed. Power is calculated from those two values.

Power (kilowatts) = torque (Nm) x rotating speed (radians per second).

It's only you backwards folk in america who need funny conversion factors to make up for imperial units.


The conversion from power to torque is equivalent to converting force to power.
Power (kilowatts) = Force (N) x Velocity (m/s)

Most people can comprehend force better than torque.



For example, a chair provides force (it holds things up) but produces no power as it's not moving.

[Alastor187]

Originally Posted by UncleBob

If there is work, then there is time.

Technically speaking work is independent of time. Regardless of whether or not time is always present, when calculating work time is irrelevant.

Originally Posted by KiwiBacon

Power (kilowatts) = torque (Nm) x rotating speed (radians per second).

It's only you backwards folk in america who need funny conversion factors to make up for imperial units.

One of the benefit of being a backwards American engineer is learning two system of units

I assuming the you are calling the following equation funny:

• Power (Horspower) = torque (lbf-ft) x rotating speed (RPM) / 5252

For your equation to be correct it should actually be:

• Power (kilowatts) = torque (Nm) x rotating speed (radians per second) / 1000

And to be fair I doubt tachometers oversea actually read rad/s, so:

• Power (kilowatts) = torque (Nm) x rotating speed (RPM) / 9549

[UncleBob]

Originally Posted by Alastor187

Technically speaking work is independent of time. Regardless of whether or not time is always present, when calculating work time is irrelevant.

explain please. The very definition of 1 HP is raising an object X distance within X time. Are you refering to a different unit of work?

[curtis73]

Originally Posted by UncleBob

explain please. The very definition of 1 HP is raising an object X distance within X time. Are you refering to a different unit of work?

Its a bit complex, since the common units like the watt, hp, and btu, originally were defined by time, they exist irrelevant of time.

You can do 100 watts of work over a period of 10 seconds or 10 years but it doesn't change the fact that 100 watts of work was done. What you're describing is watt-hours or watt-minutes.

The net result is that time has passed, but the amount of work done is existent regardless of time. Its basically a drag racers scenario. It takes 900 hp to move a 2000-lb car down the 1/4 mile in 9 seconds. The 900 hp exists regardless of the 9 seconds it took. That same 900 hp also means 5.6 seconds in the 1/8th mile, or 16 seconds in the mile, but we don't define the engine's output by its 1/4 mile time, we define it by its work done.

HP is measured in... well, HP. Not 33,000lb-ft/min. Once you take that 33,000lfm number and call it HP, you've defined the work done regardless of the time.

[Alastor187]

Originally Posted by UncleBob

explain please. The very definition of 1 HP is raising an object X distance within X time. Are you refering to a different unit of work?

Horsepower is a unit of power, not work. The definition you provided is a correct definition of power.

The equivalent definition of work would be:

raising object X distance

The SI unit would be joules (J), and the U.S Customary unit would be inch-pound-force (in-lbf) or feet-pound-force (ft-lbf).

Note: the subtle difference in the equivalent units of torque which would be N-m, lbf-in, or lbf-ft, respectively.