Power vs Torque Questionnaire -RESULTS

[Stradivarius]

Watt produced stationary steam engines, not motor vehicles - AFAIR,
& anyhow steam recip' mills, - like electric motors - produce max torque from the get go (straight from stall),
- quite unlike a hi-po ICE..

Why is it significant that Watt produced stationary steam engines? Is there any fundamental difference in terms of performance between a stationary and a unstationary engine? Is there any fundamental difference between lifting an object, working against gravity, and accelerating an object, working against the inertia? I believe Einstein (whom you refered to earlier) eagerly pointed out that there wasn't, ref. his famous elevator thought experiment.

It is true that a combustion engine does not produce any torque or power at all from the get go, as it is not even able to start without help. It basically feeds itself when it is running, but can't start that proces without external help. But why does that matter as long as we are discussing running engines?

[Richard]

See this link for '5252' explanation: http://www.epi-eng.com/piston_engine_te ... torque.htm

As that link quote rightly explains, two engines with the same power at different RPM will have the same acceleration. In contrast, two engines with the same torque at different RPM will have different acceleration.

In cars of equal weight, a 2-liter twin-cam engine that makes 300 HP at 8000 RPM (197 lb-ft) and 400 HP at 10,000 RPM (210 lb-ft) will get you out of a corner just as well as a 5-liter engine that makes 300 HP at 4000 RPM (394 lb-ft) and 400 HP at 5000 RPM (420 lb-ft).

So:

• A 300hp engine has the same acceleration as the same as a 300h engine.
• A 197lb-ft engine at 8000rpm has the same acceleration as a 394lb-ft engine at 4000rpm.

The second bullet is long winded way of saying the same thing as the first.

If you want more torque you simply change the gearing. That's why a hamster on a wheel (given suitable gearing) can generate the same torque as any steam recip' mills, Kawasaki 750/3 or a creamy long-legged petrol mill. Of course the hamster will rapidly run out of steam because it doesn't have the same amount of power even though it has the same torque.

Given your extensive experience, I suspect you know all this already. I wonder if you are being deliberately obtuse or playing word games. If not, what is your point that we've all missed?

[J.A.W.]

Actually R, I had noted earlier that even the ancients had worked out the rope/pulley - block & tackle - gearing solution..

But the hamster example is surely fictional, since if tried, the transmission losses would make it impracticable..
( & even a hypothetical hamster's power output is due to gearing, not to a - per se - high torque value).

The point is, all the input values affect the equation outcome.. but torque is the root of all shaft power..

[J.A.W.]

Watt produced stationary steam engines, not motor vehicles - AFAIR,
& anyhow steam recip' mills, - like electric motors - produce max torque from the get go (straight from stall),
- quite unlike a hi-po ICE..

Why is it significant that Watt produced stationary steam engines? Is there any fundamental difference in terms of performance between a stationary and a unstationary engine? Is there any fundamental difference between lifting an object, working against gravity, and accelerating an object, working against the inertia? I believe Einstein (whom you refered to earlier) eagerly pointed out that there wasn't, ref. his famous elevator thought experiment.

It is true that a combustion engine does not produce any torque or power at all from the get go, as it is not even able to start without help. It basically feeds itself when it is running, but can't start that proces without external help. But why does that matter as long as we are discussing running engines?

The discussion is actually about the effect of torque curve characteristics - on motor vehicle performance - no?

[machin]

torque is the root of all shaft power..

Who cares though; it can be argued either way which is more fundamental, but at the end of the day I don't need to know whether the chicken or the egg came first to enjoy an omelette...

[J.A.W.]

Because.. it is a fundamental root cause matter..

The power output measured by a dyno - is a mathematical plot - of what work the torque is doing..

Zero torque produced = zero power output..

[xxChrisxx]

Oh J.A.W you must have no power. You are all torque and no action.

[J.A.W.]

Oh J.A.W you must have no power. You are all torque and no action.

"That does not compute." L.O.L...

[mrluke]

If you know the peak power of 2 cars (with the same weights) you can tell which is quicker. If you know the peak torque of each car but not the power then you have no idea which is quicker.

[Stradivarius]

Because.. it is a fundamental root cause matter..

The power output measured by a dyno - is a mathematical plot - of what work the torque is doing..

Zero torque produced = zero power output..

And zero rpm also means zero power output. And since it was recently pointed out, I could mention that for a combustion engine, zero rpm also means zero torque, since the engine needs to run in order to feed itself and keep itself alive. So I am yet to see a valid argument that torque is more fundamental than angular velocity.

I would argue that the combustion where chemical energy stored in the fuel is released and turned into heat (which is considered an energy loss in this context) and work is even more fundamental. So if you want to be fundamental, you should look at the rate at which fuel is burned in the engine. And that tells you nothing what so ever about the torque, but it says a lot about the power. If the engine burns 10 grams of fuel per second, that is equivalent to roughly 450 kJ per second (depending on the type of fuel), which means the power input is around 450 kW. Let's say that roughly two thirds of the energy is lost to heat, giving an efficiency of 1/3, and that leaves us with a power output of roughly 150 kW or 200 hp.

The efficiency between combustion engines does not vary much, so if you are considering two cars with similar mass, the car that burns fuel at the highest rate is generally the one that accelerates fastest and has the highest top speed.

[J.A.W.]

I suggest it might be illustrative to have another look at the dyno charts - in that oft linked Superbike comparison test..

http://www.kawtriple.com/mraxl/articles ... bikes2.htm

Compare the two 3 cylinder 750cc machines (Kawasaki & Trident), 2T VS 4T, the motive torque measurements
( & calculated power output, in train, naturally)
- give a clear picture of what the fuel burn energy is doing - in terms of shaft spinning/machine performance ability..

.. & - by utilizing X2 (or 1/2) unit impulse inputs per crankshaft revolution - due to differing ICE design principles..

[J.A.W.]

A conceptual 'shadow' analogy - may be of assistance for those finding difficulty with the torque-hp continuum..

Examination of those dyno charts - which graph actual tests of Superbike engines - clearly shows..

The dynamic range (over the 'powerband'/rpm) of functional motive torque production.. which is.. then..
.. 'shadowed' .. graphically.. by the hp..
.. the hp is - mathematically calculated - from the - actual/primary - torque figures..

The torque output is the physical measure, & the hp figure shown - is its 'shadow' - as a 'fictional' mathematical construct..
..since the hp is in fact - simply an extrapolated 'artefact' of the physical/real torque curve..

[J.A.W.]

& if of interest/for contrast, included here is an automotive-use, geared shaft, gas-turbine dyno chart..
( Curiously enough, it is also an example of an - ICE design - that gives max torque from the 'get go').

http://www.turbinecar.com/turbook/pg02b.htm

[hollus]

J.A.W. , (nobody but you and now me) is discussing that there is a hard mathematical relationship between torque and power nor which is more fundamental from a physical point of view. By the way, neither is, all forces are created linear in an instantaneous view of the universe and torque only appears once you apply constrains and consider the distance to an arbitrary axis, while power only appears once you add distance and time (aka speed) to your force.
To design the materials in the vehicle or to measure its properties, by all means, use the force!
But the discussion (lesson?) was about which is more useful to evaluate vehicle performance. If you are convinced that torque is the important one there, go ahead, gear your racing vehicles for maximum torque.

[J.A.W.]

If you read the results of the empirical examples of Superbike performance testing, you will note a couple of things..

It is the "twisting force" that motivates the machines, & the hp ratings are merely a secondary extrapolation..
&, the gearing/gear shifting for best performance - is also interrelated with the characteristic shape of the torque curve..

Many max /~flat torque output electric motor powered vehicles forgo multiple gear ratio transmissions altogether.