Dyno mystery

[Corvus]

My last word on this. Maybe I need to work on explaining?

A dynamometer measures torque. Power is calculated from torque and engine speed.

Wikipedia, encyclopedia Britannica and how stuff works agree with me on this.

...........

I've lifted this line from Wikipedia :

"A chassis dynamometer, sometimes referred to as a rolling road,[3] measures power delivered to the surface of the "drive roller" by the drive wheels. "


There are different types of dynamometer.

A traditional "brake" dynamometer measures torque directly.

My point was referring to graphs produced on inertia rolling road dynamometers.

Perhaps this is more lucid than the Wikipedia one?

http://www.ktrmotorsports.com/dyno_faqs.html

[Corvus]

This is sub linked from one I posted earlier, but is a very good article.


http://www.fjr1300.info/misc/torque-power.html

From it:

"It is also possible to measure power independently of torque on an inertial dynamometer that is equipped with an accelerometer. "

The plot thickens.

[Merecat]

Only because its Sat afternoon and Im at work and bored

As given in the KTR article
Force = Mass X Acceleration

Power = Force X Velocity

All done without the aid of torque and a safety net

[Corvus]

Only because its Sat afternoon and Im at work and bored

As given in the KTR article
Force = Mass X Acceleration

Power = Force X Velocity

All done without the aid of torque and a safety net

Hee Hee.

How do you feel about the notion of abstract torque values?

[Merecat]

How do you feel about the notion of abstract torque values?

I think its something that needs to be pondered over during the last few pints of a really good session.

[Corvus]

How do you feel about the notion of abstract torque values?

I think its something that needs to be pondered over during the last few pints of a really good session.

That's exactly what I did. Now look at the mess I'm in.

Chortle.

[Corvus]

http://www.thumperclub.com/smf/index.php?topic=7132.0

The dyno curve sheet, second post on link above, illustrates clearly what I'm saying, I believe.

The three power curves portray reality as does the top (red) torque curve. But the the two lower torque curves (blue and green) are abstract, in my view.

[Corvus]

?...........

I’d think engine rpm would be the best. It tells him something, as opposed to plot it to rear wheel rpm. What else relevant can you plot it at?

I guess you're right, but that doesn't stop the torque figure being abstract.

In essence, when they apply the 1:1 correction factor, what they are doing is giving the illusion that all the gears and chains in the transmission are 1:1 ratio. In other words all the losses are present, but no reduction in speed. If all the transmission ratios were 1:1 the torque figure wouldn't be abstract. But the transmission ratios are not 1:1.

So it is abstract.

See my point?

[Corvus]

Never mind my opinion. The hp formula should prove beyond doubt that the torque figures are abstract.

And it does. Apply the correct information and it disagrees with the graph.

Use the graph for the xbr500 I posted above as a test case.

[Tapio]

http://www.thumperclub.com/smf/index.php?topic=7132.0

The dyno curve sheet, second post on link above, illustrates clearly what I'm saying, I believe.

The three power curves portray reality as does the top (red) torque curve. But the the two lower torque curves (blue and green) are abstract, in my view.

Sorry, but I really don’t understand. Here’s how I see that dyno sheet:
First, you measure the torque at the rear wheel. This is the only thing that the dyno actually measures. This gives the green torque curve.

Then, using a correction factor to compensate for losses in FD and prop shaft hooke joints you get torque at gearbox output. This is the blue torque line.

Again, using another correction factor, you get torque at the crank. This is the red torque line.

From these, the corresponding power curves are calculated.

So, the only true curve in that sheet is the green torque curve. The rest is just math.

//T

[Corvus]

http://www.thumperclub.com/smf/index.php?topic=7132.0

The dyno curve sheet, second post on link above, illustrates clearly what I'm saying, I believe.

The three power curves portray reality as does the top (red) torque curve. But the the two lower torque curves (blue and green) are abstract, in my view.

Sorry, but I really don’t understand. Here’s how I see that dyno sheet:
First, you measure the torque at the rear wheel. This is the only thing that the dyno actually measures. This gives the green torque curve.

Then, using a correction factor to compensate for losses in FD and prop shaft hooke joints you get torque at gearbox output. This is the blue torque line.

Again, using another correction factor, you get torque at the crank. This is the red torque line.

From these, the corresponding power curves are calculated.

So, the only true curve in that sheet is the green torque curve. The rest is just math.

//T

Hi tapio, hope you are well. You probably won't be surprised to find that I disagree, with respect. The xbr500 graph is useful for the purpose of my point ,trying to prove the abstract nature of the torque curves, because it differs from a lot of others in that it prints out three sets of curve ( supposedly) representing crank, gearbox and rear wheel figures.

Here's how I see the dyno sheet:-

Tapio: "First, you measure the torque at the rear wheel. This is the only thing that the dyno actually measures. This gives the green torque curve."

I thought we'd seen that it is possible to measure power directly, without necessarily measuring torque, and that some dyno's are equipped to do this. But, anyway, this is not relevant to my point.

For those dynamometers that do measure rear wheel torque, the green torque curve is not it. No way. The green torque curve is abstract. It doesn't actually exist. The green power curve is real, but not the green torque curve. I think the green power curve has been produced from rear wheel torque measurements, but these values are not the ones we see on the green torque curve.

Tapio: "Then, using a correction factor to compensate for losses in FD and prop shaft hooke joints you get torque at gearbox output. This is the blue torque line."

No way. The losses are represented, real world, in the blue power curve, but not the blue torque curve.

Tapio: "Again, using another correction factor, you get torque at the crank. This is the red torque line."

Yes, I agree for the red torque curve. Because the speeds on the graph are clearly crankshaft speeds. The torque values shown here will actually have existed at the speeds shown.

Tapio: "From these, the corresponding power curves are calculated."

This is where I believe something subtle has happened. The power curve comes first. Not in what is "fealt" by the rollers, but what is actually used by the computer. It gathers information to produce a rear wheel power curve, the green one, but then a human comes along and "corrects" the torque figure to crankshaft speed. So, to be clear, that is rear wheel power with a torque curve produced from it at crankshaft speed. Clearly abstract. One of the links I posted at the beginning refers to this as "back calculating". I see that statement as confirmation that the torque curve we see is produced FROM the power curve. Not the other way around.

Tapio: "So, the only true curve in that sheet is the green torque curve. The rest is just math."

I disagree. The only true torque curve is the red one. True in that it represents reality, not in that it was directly measured.

The only torque curve, in our example, that stands up to testing with the hp formula is the red one. That's because it's the only one where the power and rpm figures represent what happened.

For the blue and green sets of curves, the power is real life but the torque doesn't fit into the hp formula because the rpm value is incorrect.

Put in the actual rpm values for the shafts concerned and you will get a very different torque value.

This is not an attack on any process or the way things are done. Just an observation at how abstract it is. It is fascinating.

[Herb]

Corvus, you think too much. Obviously you are not having enough alcohol in the evenings. Can I recommend Stowford Press. Things will be much clearer then.

[Corvus]

Corvus, you think too much. Obviously you are not having enough alcohol in the evenings. Can I recommend Stowford Press. Things will be much clearer then.

Bloody hell! Someone's watching.

Hee Hee.

Not tried that one. But I shall!

Come on, give us your thoughts on the magical mystery torque tour.

[el-nicko]

.

I'm getting one of my 'heads' again.

[Herb]

Corvus, you think too much. Obviously you are not having enough alcohol in the evenings. Can I recommend Stowford Press. Things will be much clearer then.

Bloody hell! Someone's watching.

Hee Hee.

Not tried that one. But I shall!

Come on, give us your thoughts on the magical mystery torque tour.

I am not going to go back over 5 pages of posts. I will say, the curves provided by a dyno are a representation of what the engine is doing, utilising various measurements and calculations to derive a dataset that can be compared to other datasets derived in the same manner.

That way, changes can be tracked and analysed and future changes planned. It's a tool. Ultimately what you get from the tool will depend on the skill and understanding of the person analysing the data.