Dyno graphs

[chickenstrip]

Do they tell you all you need to know about how a bike will deliver it's power? Can you look at one and say, right, there'll be a noticeable "kick" at such-and-such revs that you'd feel when riding?

Or to put it another way, can you look at a dyno chart of a bike you've never ridden before and say, "this is how it will feel to ride?"

I'm dubious that you can, and what I've seen so far, going by the bike I'm most familiar with, bears me out. If I'm wrong, I'd like to understand why.
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[talkToTheHat]

Not with the one graph, they'll typically show what happens at WOT. Won't tell you anything about what happens as you roll on in terms of smoothness and controllability, or anything about part throttle or engine braking behaviour. For most usages, part and varied throttle performance and engine braking behaviour defines how the bike feels to ride, along with chassis characteristics that govern how the bike stops and goes. The same engine that causes a short high bike to rear up and punch you in the chest/face might feel much tamer in a longer and lower bike.

One can programmatically study a set of transitional behaviours on a decent research dyno where the test equipment receives engine rpm and can sent throttle inputs, but you will get much more data than a simple torque/power graph. This is done extensively durning modern engine development, usually in conjunction with data from the air intake, exhaust gas analysis and noise analysis.

Specific example: pumper carbs give you instant enrichment during a wind on, CV carbs briefly lean out, at constraint full throttle there will be little difference yet the feel of the engine will be totally different.
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[Rogerborg]

[Bikeless]

To a degree yes but when I had the Fireblade,a change of 122 jets down to 116 jets gave it 5 more horsepower and a better curve but it felt less powerful when riding it,putting the 122s back in made it feel more powerful even though the dyno said otherwise.

[G]

[chris-red]

Dy/Dx
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[chickenstrip]

Ok G, here's what the dyno graph doesn't tell you: how quickly the power increases with the revs*, in other words, over time. All it tells you is what power it is making at any given revs, not how quickly the motor spins up at any point when the throttle is opened. ??

*not well worded. More, how quickly the revs rise over time. So a better graph might be revs/time on opening the throttle, to give an idea of how it will feel to ride.
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[G]

Yes, it does.
At least, if you know other factors such as gearing, weight, wind resistance and so on, or are willing to assume they are similar enough between two compared models to not be of worry.
Gearing is one that people often bring up; explaining how an SV650, say, has loads of low down power compared to an R6.
But then we see that's it's actually geared 50% lower; it feels like it's got more power low down in the rev range actually because it's lower geared - the R6 would quite likely have more if you geared it to be the same as the SV.

This is basically the exact information a power graph DOES give!

[stevo as b4]

Chickenstrip, I kind of understand what you mean and also what G is referring to.

The backside in the seat dyno is very innacurate and the potential for the sunny day placebo effect is massive too. 5bhp +/- would on a big bike be impossible for your arse to measure.


The dyno does show very well how a bike makes it's power over the rev range, (have a look at a tuned RG500 dyno chart if you want to see how dramatically it can show the rate of power increase)

100% throttle pulls in a fixed gear give an overall indication of the engine's delivery and how it pulls over the rev range.

50% throttle runs also show stuff like how long it's making over a set bhp across the rev range etc (area under the curve)

An all gears run can show the thrust and torque developed at the rear wheel through the gears, and also how the gearing affects the thrust available etc. I think this is what G is often referring to when he pulls out his big twins vs IL4 litre charts!

[Kickstart]

Hi

What is better for knowing how the bike feels is to look at the torque curve rather than the power curve. Power can be increasing while torque is dropping away (will happen with pretty much any bike), and it is the change in torque that you feel.

All the best

Keith
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[chickenstrip]

I'm actually not saying G is wrong, but I think he has missed my point.


https://i1291.photobucket.com/albums/b550/nicknicklxs/FZS1000withIvansFullMontyBMCfilterslip-oncanG-Forceportedcarbrubbers_zps55522230.jpg

This is the dyno curve for an FZS1000 in a pretty much identical state of tune to mine. You can see that it's very linear, maybe just a very slight step just over 7k rpm. But this belies what you feel when pinning it through that rev range on the road. Then, the step at 7k feels very marked, not something you'd be thinking "am I imagining this?" It gives your arms a very noticeable yank, and especially as you're sat pretty upright, you have to hang on tight. The rear end squats and the thing takes off. And I know plenty of people with the same bike tuned thus who would agree with this. And once given this dyno graph, the fact that the bike is not stock is immaterial for illustrating my point.

I'm not trying to compare it to any other bike, and I fully agree that if you know the gearing, the weight, what kind of traction the rear tyre gets and the aerodynamics of the bike, you are probably quite well placed to predict how it will feel on the road. All I'm saying is that the dyno curve alone does not tell you to expect this. This is my point. You would be better served with a graph of revs/time to show what actually is happening as far as the measured acceleration of the bike is concerned..........








I think.....
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[G]

I would, respectfully*, question whether you understand the concept of 'power'. I might also suggest that maybe you need to work out if you ARE 'imagining' this!

Is this with a most definitely wide open throttle?
A lot of people don't hold throttle wide open when they think are - I know I've been guilty of this in the past.

Could it be something to do with a TRE style device that only works in certain gears?

In the end power torque/power pretty directly relates to the acceleration possible by the engine - this is why people make the graphs with these figures.

*Some may ask if this is actually the case.

[Kickstart]

Hi

Very smooth power curve. If it is still running like that then there shouldn't be any real kick in the delivery, but plenty of things could change that would cause a kick (such as the EXUP valve sticking - or pegged open).

This is a bit more fun:-

https://www.bikegraph.co.uk/TorqueGraph.php?Id=19&x_max=800&y_max=500

All the best

Keith
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[Pete.]

It's not hard to envisage the distinction between power and torque. Torque is 'effort made', it's the actual levering force turning the wheel (via gears).
Power is 'work done' or 'effort made over time'
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[chickenstrip]

[Kickstart]

[G]

[chickenstrip]

[Kickstart]

[talkToTheHat]

[chickenstrip]

[Northern Monkey]

[Marlin]

[talkToTheHat]

That wan't pointed at anyone on here, it was a meatloaf reference that means a little to me that my not quite father in law has wrecked more bikes through his own stupidity than I would like to count, and a clan elder from a generation previous nearly died when he throw a black shadow around a corner, forgot about the plank bridge and landed in a drainage ditch.

EDIT: chris-red beat me to this but I missed it, but it was little explained

Back to engineering

Work = Force x Distance travelled
Power = Rate of Work = Force x Distance / time
Torque = Force x displaceent vector

so
Power = Torque x 2pi x rotational speed
Some unit conversion required if not working in Watts, Newtons, Metres and Rev/second

EDIT: remembered unit conversions
Power (BHP) = Torque (lbs.ft) x Shaft Speed (revs/min) / 5252
Power (W) = Torque (Nm) x Shaft Speed (revs/min) x 2 x pi / 60

Or on a chart of power and torque against RPM, the power is the area under the torque curve, and the torque is the gradient of the power curve. Thus a horizontal torque will give perfectly linear increasing power. Make of that what you will.

I think the FZR chart is a little misleading as the torque has been scaled to appear extra flat. That scale should top out at 80 or so Nm not 150. Looking carefully that chart suggests torque reduces not long after 7k, as does the power increase. That said it looks like a whole heap of fun as a road bike and reasonably well mannered.

Factor in a constant (ish) rolling drag and aero drag that's thereabout proportional to the square of the speed, but note aero drag can suddenly decrease as airflow over a high drag part stalls.

[Bubblin77]