Dyno mystery

[Corvus]

Ahm oot

/Bannatyne.

Shame.

All I need to know, with reference to Nike's graph is whether the power curve is rear wheel power?

All I need is yes or no.

[conkerman]

Have you looked at the pic?

The answer is yes by the way. So uncorrected for coastdown. Although it does look healthy for a blade so I prepare to be shot down.

Must be a Hoot!

[Corvus]

Have you looked at the pic?

The answer is yes by the way. So uncorrected for coastdown. Although it does look healthy for a blade so I prepare to be shot down.

Must be a Hoot!

Thanks. Yes of course I've looked. This brings me right back.

If you plot a torque curve at engine speed against power values obtained at rear wheel speed, with all the losses, then the torque curve is abstract. The power as shown will actually have happened but the torque won't have.

If you don't agree that's fine. It could be me that's wrong. But do you want me to try to prove what I'm saying? There's a chance I'll end up proving myself wrong!

How about it?

[Corvus]

The posted graph.

I don't know if there is additional information on another sheet, but the graph sheet is ambiguous as to whether the figures are crankshaft or rear wheel. The rpm is obviously crankshaft, but there is reference to "wheel" also.

My two posted links explain what is happening don't they?

Maybe we're not actually disagreeing, except it's only me who sees this ad abstract

[el-nicko]

Going back to Nick's curve. He hasn't answered my question. Is the graph showing rear wheel power? Just a yes or no please.

Well, it seems (the equivalent to) a thousand words is not enough and to be honest I must say, I don't know, and, that this discussion/theorizing has been going waaaaaay over my head all along.

The graph (I've posted) is not mine but one I scanned from another forum and simply illustrates, visually, for that particular customers edification, the effect on his bike engine, pre and post the fitting and calibrating of a Power Commander V (5) fuel management devise.

With respect, dare I say, I feel all this abstract chit-chat is, irrelevant to the average 'biker-in-the-street' since all we're interested in is a nice picture illustrating that, by comparison, some positive/perceived improvement to an engines characteristics has taken place. At bottom, it's of no consequence to most of us whether the 'units' displayed are horses, cabbages or Cowry shells as long as we're all singing from the same song-sheet so to speak, and the print-out confirms, (hopefully illustrated by way of a lovely, smooth parabolic curve) that we have more of them than before and, consequently haven't wasted any hard-earned cash chasing our tails.

Finally, having raised the subject of 'hard-earned-cash' and, purely out of idle curiosity, would it be too rude to ask 'Corvus' what he does for a living?

conkerman wrote:
Ahm oot!

Me too.

ATB, Nick.

Message Ends

[conkerman]

Maybe we're not actually disagreeing, except it's only me who sees this ad abstract

I thnk so.

If that dyno curve is as it appears. It is a plot of 'effective torque/power' making from the crank to the roller, normalising for the torque multiplication effect of the gearbox.

We could probably sort this out in 5 min in the pub, I suggest we leave it until we get the opportunity.

[Corvus]

Going back to Nick's curve. He hasn't answered my question. Is the graph showing rear wheel power? Just a yes or no please.

Well, it seems (the equivalent to) a thousand words is not enough and to be honest I must say, I don't know, and, that this discussion/theorizing has been going waaaaaay over my head all along.

The graph (I've posted) is not mine but one I scanned from another forum and simply illustrates, visually, for that particular customers edification, the effect on his bike engine, pre and post the fitting and calibrating of a Power Commander V (5) fuel management devise.

With respect, dare I say, I feel all this abstract chit-chat is, irrelevant to the average 'biker-in-the-street' since all we're interested in is a nice picture illustrating that, by comparison, some positive/perceived improvement to an engines characteristics has taken place. At bottom, it's of no consequence to most of us whether the 'units' displayed are horses, cabbages or Cowry shells as long as we're all singing from the same song-sheet so to speak, and the print-out confirms, (hopefully illustrated by way of a lovely, smooth parabolic curve) that we have more of them than before and, consequently haven't wasted any hard-earned cash chasing our tails.

Finally, having raised the subject of 'hard-earned-cash' and, purely out of idle curiosity, would it be too rude to ask 'Corvus' what he does for a living.

conkerman wrote:
Ahm oot!

Me too.

ATB, Nick.

Message Ends

Hi Nick!

Wish you'd have spoken earlier. I was worried in case you were in some way taking offence. I can see you're not.

That helps!

Fact is, I actually like thinking about all this stuff. Sorry!

[Corvus]

Ok, so we are back to dyno power curves being rear wheel. Fine, that's what I thought. Don't have a problem seeing why and how. But the moment you plot a torque curve against it, but at engine speed, you get an abstract torque value. The torque value, expressed thus, won't have actually occurred. I've never thought it wouldn't be of use or have some meaning. I can see how we are kind of forced into crunching the numbers this way. But that wasn't my point.

Actual crankshaft torque occurs before any losses, so it will be a higher figure than the one we get shown. The best description I can think to give the torque value in question is "effective crankshaft torque".

That is the crankshaft torque but with all the transmission losses about to happen pre removed. As the losses occur, unfortunately it is the gear meshes which cause them and of course this multiplies the torque. The torque value won't have actually occurred anywhere in the transmission. Doing this also plays havoc with the power curve. The power is accurate and "as measured" but unfortunately it wasn't measured at the speed shown on the curves. The speed shown on the curves is crankshaft speed. The rear wheel power will have occurred at rear wheel speed (to state the obvious), but that makes the speed abstract not the actual power value.

Think about the curve posted by nick. Pick any spot on the power curve and then add back an estimate of the losses. Use 10% for the sake of argument. Then use the hp formula to get a torque figure. This will be actual crankshaft torque. It will have occurred at that value on the crankshaft. The torque figure shown on the graph won't have. It won't have occurred anywhere.

I reckon.

[el-nicko]

.


This should keep you quite for a while mate. Especially the last bit.


http://www.mcnews.com/mcn/technical/2013JanPerfIndx.pdf

[Corvus]

.


This should keep you quite for a while mate. Especially the last bit.


http://www.mcnews.com/mcn/technical/2013JanPerfIndx.pdf

Ha ha. Just spotted what you mean. Yeah a field day! Like a kid in sweet shop.

Oo you are a tinker.

[Corvus]

Perhaps it has been worth it.

I've got at least one forum member looking at this in a slightly different context.

Admit it nick. You wouldn't have given those "rear wheel" torque figures a second thought a thousand words ago.

Who's gonna write in? Me or you?

[el-nicko]

Perhaps it has been worth it.

I've got at least one forum member looking at this in a slightly different context.

Admit it nick. You wouldn't have given those "rear wheel" torque figures a second thought a thousand words ago.

Who's gonna write in? Me or you?

[Corvus]

Perhaps it has been worth it.

I've got at least one forum member looking at this in a slightly different context.

Admit it nick. You wouldn't have given those "rear wheel" torque figures a second thought a thousand words ago.

Who's gonna write in? Me or you?

Ah. That's the same context you started with. Oh well.

Ya gotta larf.

[Corvus]

Came across these.

Make interesting reading.

http://wotid.com/dyno/content/view/18/34/

http://www.largiader.com/articles/torque.html

http://vettenet.org/torquehp.html

[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.