Power vs Torque Questionnaire -RESULTS

[J.A.W.]

No C, not for disagreement, but for being doctrinaire/dogmatic/purblind - perhaps?

But - I think whoever delivered the downvote ought really to provide their own reasoning..

I will comment that odd 'reputation' voting (& sometimes grumpy moderation) aside,
- this forum is a generally very open/fairly run, ideas tolerant operation.

[Charlatan]

Trying to explain natural laws is being doctrinaire/dogmatic/purblind on this forum?

[J.A.W.]

"Natural laws"? http://www.lesswrong.com/lw/ct3/natural ... not_rules/

Motor vehicular operation done for pleasure - is more involving than mere rote recitation/reiteration - of Newtonian physics..

[machin]

If you were to put a ratchet socket wrench on the Kawasaki crank when it was spinning at 6,000rpm
& lock the wrench while attempting to stall the engine by exerting your arm strength - what would be the result?

Now you are getting confused by talking about two different things: the effect that you note here is actually the effect of trying instantly to decelerate something from a high speed which has a very high amount of inertia... If you turned the engine "off" (i.e. cut all fuel to the cylinders) before attempting this "experiment" the engine would be producing no torque at all, but it would still be spinning bloody fast (for a short amount of time), hence have a lot of kinetic energy, and you trying to stop it using your arm is only going to result in one of very few outcomes: probably a broken arm.

A few posts back it was mentioned that torque curves can be used to discern the "nature" of an engine's output "Sporty" or "Tractor-like", but since a power curve is just "a more useful expression of the torque and RPM outputs of an engine" you can determine the same nature from an engine's equivalent power curve:-




So the "Rising torque curve" ("Sporty engine") is characterised by an exponentially increasing power curve, and the "falling torque curve" (Tractor Engine) is characterised by a bell-shaped or flat-ish power curve... As I said a few pages back; the advantage of the power curve is it allows you instantly to see what RPM you should be aiming for to get the most performance out of your engine (Where it makes most power): whether that engine is used to accelerate a car, lift weights, or do any other type of work.

[J.A.W.]

Rather than "getting confused" by fanciful/imaginary line plots on made up graphs, machin..
..why not actually refer the real examples of dyno charts presented in the linked data sets..

If you hit the kill switch on a low inertia mill - like the Kawasaki 750/3 - it stops pretty quickly..
..but powered up - it would indeed - likely rip your arm right out of its socket..

[autogyro]

Even accurate dyno data is insufficient to conclude anything meaningful.
You also need the characteristics of the vehicle or machine the engine is applied to and the environment it is designed to work in.
It is no use trying to simplify it down to a few lines on a graph.
It usually comes down to one question.
How small and how light can you make the gear train components.

[machin]

Rather than "getting confused" by fanciful/imaginary line plots on made up graphs, machin..
..why not actually refer the real examples of dyno charts presented in the linked data sets..

If you hit the kill switch on a low inertia mill - like the Kawasaki 750/3 - it stops pretty quickly..
..but powered up - it would indeed - likely rip your arm right out of its socket..

Try turning a bicycle upside down and spin up the front wheel, and then try stopping that with your hand... no power/torque is being applied to the wheel; it'll still bloody hurt when you try and stop it; it is all about the inertia in that instance, which is really nothing to do with what we're talking about here.

Please remind me again what you think Power and Torque are, because to be honest, it appears to have been lost within this thread, and I think it is better if you concisely say what you think the two are, so that we can try and figure out where the error is creeping in....???

For example, do you accept that an engine's power curve can be generated from its Torque curve?

[J.A.W.]

& if anyone would care to actually consider the (previously provided) real case/data set, here it is again..

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

Interestingly A-G, the built-up multiple rolling bearing element crankshaft of the 2T Kawasaki 750/3
& its discrete cylinder functions - allowed for fairly simple alterations in crankshaft angle configurations..

The standard machine featured an even firing interval 120 degree crank, & a 'tringle' ( all 3 firing together)
configuration was tried for dirt track ( an early attempt at 'big bang'), but the primary drive spur gear failed
- when tasked to take all three power impulses simultaneously - though the same gear teeth interface..
..which had been designed to accept 1/3 the power impulses, 120` apart..

[machin]

Below I attach one of those charts...



I've simply copied the torque curve (my version is shown in blue below the "official" graph).

For each point on that torque curve I've simply multiplied the Torque (lbft) by the Speed (RPM)...
(I've indicated one such point on the chart above: 7200 rpm and 45.5lbft = 327,600)

....and then plotted a curve of (lbftxRPM) against RPM.... which is shown in red...

Note that the result is a curve which has the EXACT SAME SHAPE AS the official power curve....

To convert from "lbft x RPM" to BHP, simply divide by 5252... and you'll now get a chart that is EXACTLY the same as the "official" power curve given above....

[Richard]

....

As many others have pointed out, power and torque are different ways of describing the same thing.

What is your point?

[Charlatan]

...
As many others have pointed out, power and torque are different ways of describing the same thing.
...

No it's not, not even close.

[machin]

It is correct to say that engine performance can be accurately described using EITHER

torque and RPM

Or

Power

And the result will be the same... Which I believe is the point Richard was making.

My argument is that "Power" is easier to understand as involves one number... Whereas torque and RPM needs two simultaneously.

[Richard]

My argument is that "Power" is easier to understand as involves one number... Whereas torque and RPM needs two simultaneously.

Indeed. Power = Torque x RPM and Torque = Power/RPM. So I'm puzzled why JAW and Charlatan are naysayers. We all know that they know that simple formula perfectly well?

Yes power is a useful metric and the only relevant one for vehicle performance as demonstrated by Machin et al. However torque is needed if you want to know the force in something. There's a clue in the name because we all know torque is force ... don't we?

You may also have situations where torque alone is an interesting parameter. If you are dimensioning the parts of the drive train, you need to make sure they are strong enough to handle the loads and that means you need to know the torque. But that is not related to performance.

In every vehicle model I have ever built, the engine/powertrain is defined using a torque curve. The traction control, engine control and differential control algorithms that I have seen and worked with all use engine torque to calculate wheel forces in their internal modelisation. When I want to calculate the yaw torque due to the differential locking I use torques/forces.

Anyway, next week on F1T: Which end should you crack your egg? Pointy or round end?

[machin]

We all know that they know that simple formula perfectly well?

The problem of course is that most magazines/websites talk about the two things as if they are completely unrelated.. so I think it is not correct to say that everyone knows that Power= Torque x Speed, or if they do know it they might not quite get what that actually means (i.e. that you can derive the power curve from the torque curve and vice versa) because of the aforementioned magazine articles...

????

[Charlatan]

...
However torque is needed if you want to know the force in something.
...

I think this is where you are missing the point; Power is Force times Speed, no reason to involve Torque to figure out the Force.