Help me understand Dyno's. this makes no sense.

[skip68]

I've read threads here and on my R1 forum AND other sites.   IT seems that there is serious confusion between real HP,  different Dyno's and power losses through the transmission.  
I'll use my bike for example but the principles are scientifically the same.  
My bike is supposed to have 180+- HP at the crank.  
It was dyno'd by previous owner at around 152 at the wheel.  
How can this be right?   I have more trust in car guys with dyno numbers than bike or rice burner guys.  
On a stand my bike can idle in 6th gear with the wheel spinning of course and using very little effort.    So how the hell is it using about 28HP to do this?   Obviously this doesn't require 28HP from the crank to the tire.  I've also seen this math used in cars where we're talking about HP losses through transmission.  
I've seen tire size, gear ratios and such used for calculating numbers.   So here's my other and main question.  

Like ringing the bell with a hammer at a carnival,
Why don't all Dyno's have a simple baseline of force needed to spin up to a certain speed and force?   I don't care what is spinning the tire or gearing (car or bike) used.  Wouldn't that give us real numbers?     I'm basically convinced that a dyno is really best used for tuning purposes only so you can see improvements and not a reliable source for true HP.  

If I change gearing I gain more acceleration and more force to the ground/dyno from the tire.  So, that means I'm making more power correct?    

[Back N Black]

Good questions, i can't answer but interested to see response. 

[maxwellwedge]

There is always a frictional loss from the end of the crank to the pavement.....everything after the crank is an HP loss. How much of a loss depends on how many moving parts it goes through before it hits the pavement....and how efficient they are - etc.
15-20% of a frictional loss is not uncommon.
There is a Physics 101 explanation......but that is beyond the scope of this dude 

[skip68]

I believe a dyno should be the amount of force needed to move something so far.  
Shouldn't that be correct?     Or, is the time it takes to achieve this also part of the equation?   If time, distance and force is the equation then gearing is an essential power multiplier or subtractor.  
Therefore, if you take the same car that runs let's say a 12sec 1/4, change the gears and now it's running a 11sec 1/4 mile with faster speed, it has more power to the ground.   Right.  
If you dyno'd before and after gear change wouldn't you see higher power after the gearing change?    
Or are you just moving the power so it comes in sooner and is being used more efficiently?  
Sorry if this is getting deep but I've wondered about this stuff for years as I'm sure others have.  

[Troy]

Well, one thing, you didn't test the engine alone then at the wheel to compare like numbers so you really have no idea what the real loss is. One is a "spec" measurement and the other is "as tested". It does seem excessive for a motorcycle.

Tire size and gear ratio don't add or subtract from the power output other than the drag (parasitic loss) that they may impart. Gears and tires are levers and help focus the energy. An automatic transmission could have exactly the same gear ratios as a manual but will transfer less power (in most cases) because there's more moving parts and the torque converter allows some slippage just by design (I'd have to read up on lockup converters to see if they truly are 100% efficient).

The design of the dyno and the calibration has a lot to do with different readings. Weather (air density, humidity, etc.) also plays a part but most should be able to correct the numbers to a standard value.

Troy

[crj1968]

I cant speak to it all- but changing gearing doesn't make more power it just uses it in a different way.

If you run 4.88's you might get down the 1/4 mile quicker, but you wont be going 140 miles per hour down the freeway like you could with 2.76's

[skip68]

There are so many factors that a dyno needs to calculate and that's where the conflict starts.  Plus, different types of Dyno's.   
That's why there should be a more basic mechanical type of dyno I think.     

[skip68]

The design of the dyno and the calibration has a lot to do with different readings. Weather (air density, humidity, etc.) also plays a part but most should be able to correct the numbers to a standard value.

Troy

That right there can be and probably is a huge factor.  Which is why I'd like to see a more mechanical type designed.   I think it'd take the guess work and human mistakes or fudging out of the picture.  
So then I guess I'm right by saying that a dyno is basically better used as a tuning tool for maximizing power.  Whether the numbers are low or fluffed the ability to make changes and see the increase is what's beneficial about a dyno.   Since every shop says their dyno is right is just a sales pitch far as you really know.   

[John_Kunkel]

Obviously this doesn't require 28HP from the crank to the tire.

Think of it this way; suppose you could swim a lap in 15 seconds, then drain the pool and fill it with mud...you're body strength didn't change but the lap would be a lot slower.

[cdr]

the more force applied, the more friction, at idle with the rear tire off the ground there is no load,pressure, on the gears, chain, ect...the more power the engine makes the more loss. 

[Green71R/T]

A dyno also wouldn't be accurate in the bottom (or top) 5% of its measuring range.

[skip68]

Ok cdr and John, that makes sense.  I still don't see there's that much of a load though.   Man, I'm getting more confused.    
But, like Troy said about spec HP, I really have no idea what the true hp at the crank is other than what the manufacturer claims which can be fluffed.   Seems like they all fudge the numbers.
   
Either all the manufacturers have been lying for ever or they're using different dyno methods.  Because I'm just not going to believe I've got (and all liter bikes) a almost 30HP loss from the crank to the ground.   

[A383Wing]

maybe you need to loose some weight there, Skippy....you would have more horsepower left over to use then

[ws23rt]

Obviously this doesn't require 28HP from the crank to the tire.

Think of it this way; suppose you could swim a lap in 15 seconds, then drain the pool and fill it with mud...you're body strength didn't change but the lap would be a lot slower.

This is a pretty good way to look at it.

Horse power is a unit of measure that describes an amount of work being done.  Swimming the pool of water is about moving through (displacing) water. Mud is thicker so for a given HP expended less distance is covered.

If an engine is running through a dyno the dyno is creating a resistance in order to measure the HP. The dyno is like the mud in the pool.

A part of this conversation that seems to trip up the mind is torque.  Lets say we have a converter on the motor and it's output is held (to not rotate). The holding device will see torque but not HP. ( If no shaft rotation happens past the converter no horse power is measured).  In this case all the HP is being converted into heat in the converter.  The parasitic losses in a drive train show up as heat instead of rotational movement.

Any transmission or gearing change made is just a way of multiplying or reducing torque and is a separate unit of measure that is independent of HP.

[HPP]

There are SAE standards for measuring horsepower, which we laymen tend to call gross and net but there are others, and they have fancy numbers to explain each one. So any manufacturer can say they measured their powerplant at SAE standard XXX and not be lying. They may also take a prototype or hand built engine to use as their published baseline that works at a level of performance a mass assembled unit cannot expect to achieve. The term blueprinting comes to mind here. So yes, the ideal engine in your motorcycle measured under a under liberal standard could, in the real world, measure nearly 30 hp more than what you actually have.

As others have said, we also have atmospheric variables. Ideally a dyno readout should adjust those to whatever SAE standard they are measuring to.

On top of changes in air pressure, humidity, etc, you also have changes in road resistance, tire slip, grade, etc that all can alter total measured output. Dynos do not measure free wheeling horsepower, so they are imparting some sort of drag into the equation to generate the numbers, so different types and levels of force will impact read out from a specific dyno. This is why some will say some dynos are more stingy with numbers while others are more liberal.

We also could get in to discussions about all the different dyno types and their plus and minuses that will throw another level of variables into the whole process.

[skip68]

Ok, then that goes along with what I've said over the years that torque is what moves you, not hp.  I know changing sprockets/gears will develop more torque and acceleration.  
So does that show up on a dyno as the same HP but higher torque?  

[ws23rt]

Ok, then that goes along with what I've said over the years that torque is what moves you, not hp.  I know changing sprockets/gears will develop more torque and acceleration.  
So does that show up on a dyno as the same HP but higher torque?  

Changing sprockets/gears just moves the torque value to a different RPM.  Horse power is something that will not change by shifting gears.

A low gear will feel stronger but not last long.  Torque gets you up to speed but horse power is what holds the speed. When we accelerate we are feeling torque based on the gear chosen. At speed we are using horse power but don't "feel" it.

[skip68]

Thanks HPP & WS.     
So then how do you know what the true HP loss is through the drive train if you don't know the true spec HP?   I guess it doesn't really matter much.  

[ws23rt]

I'd like to add something else to this topic about torque and horse power.
When I was waiting for my opportunity to buy my hellcat I was reading hundreds of accounts from buyers about how it was to drive one. The overwhelming comment was it put a smile on your face.
I felt what they were talking about and it is for the most part low end torque. ---This car makes 400 ft lbs at about 1200 RPM. ---
In one spot on the interstate in South Dakota I put the horse power meter on so I could see what 700 hp felt like. At 160 mph it was pulling hard but only making 585 hp (just the one quick test below the max hp rpm). The freeway got small at that speed and I wimped out

I guess my point is that when someone refers to feeling the power I say that's not true. I've been at that speed a few times in my earlier life but never felt the acceleration pull like that at that speed in a stock car.

[skip68]

 . Geezus.   

[Bronzedodge]

Tire size and gear ratio don't add or subtract from the power output other than the drag (parasitic loss) that they may impart. Gears and tires are levers and help focus the energy. An automatic transmission could have exactly the same gear ratios as a manual but will transfer less power (in most cases) because there's more moving parts and the torque converter allows some slippage just by design
Troy

John Kunkel and Troy said it well.  I'll just add this.
Folks talk about the numbers but seem to forget the definitions.  Horsepower n. unit of power equal to 550 foot pounds per second.  It's a measure of power over time.  Torque is rotating force, measured in some unit, sometimes foot-pounds.  See the relationship there.  I could drone on about the 5252 constant and why the curves always cross at that rpm, but there's better articles on the web.  The only other thing to say is that Dynos are a gauge.  Like a box of pressure gauges or the old pocket thermometers, if you start to compare them, you'll get different numbers.  Or, when was dyno "X" calibrated last?  

[skip68]

 . I just looked at some dyno pictures in general.   That's crazy but they all do seem to cross at 5252 more or less.  This is way above me.   I've got the basic picture now but man, this is more complex than I originally thought.  No wonder so many get confused and questionable printouts.   Thanks guys. 
I still want a more mechanical base method at least for torque.   

[Paul G]

Something else to consider and I hope I can get this thought out of my head correctly

Acceleration and time? Do they have a factor?

Going form 0 RPM to 6000 RPM is a factor of time. How much time does it take to spin a device, transmission, driveline, etc., from 0 RPM to to a maximum RPM?

Lets say an engine that makes 200 hp/tq takes 8 seconds on a chassis dyno to spin to 6000 RPM. Now try a more powerful engine that makes 500 hp/tq turning the same driveline on the same dyno.  I would think it should spin to 6000 RPM in much less time.

Compare the crank output power of both engines, vs. loaded output power of both engines? Does the stronger engine loose more power turning the same driveline? Could that be because it does it in less time?  

That is what we see in real world dyno numbers. Stronger engines show more driveline loss percentage. Which doesnt make sense to my simple mind.

[skip68]

That completely makes no sense to me also.   The more power something has, the LESS energy is needed to accomplish the same task.   Isn't that correct?    
With that theory, a transmission should only require X amount of power to operate regardless of what engine it's bolted to.  
Take a 440 and a 383.  Both engines should see the same amount of loss through the transmission if you used the same transmission testing both motors.   Right    

     If the 383 dyno'd at say 350HP, then dyno'd at 275HP on a chassis dyno that's a 75HP loss.  
Now take the 440 and say it dyno'd at 500HP, put it in the same chassis the 383 was in and it should dyno with the same 75HP loss at 425HP.   Correct?    Or would there be less loss because the more powerful 440 takes less energy to spin the drive train?

Kinda like the water pump theory.  A water pump requires X amount of power to pump water at 3,000rpm regardless of what engine is driving it.   The transmission is basically a pump power converter.   

[Paul G]

That completely makes no sense to me also.   The more power something has, the LESS energy is needed to accomplish the same task.   Isn't that correct?      
With that theory, a transmission should only require X amount of power to operate regardless of what engine it's bolted to. 
Take a 440 and a 383.  Both engines should see the same amount of loss through the transmission if you used the same transmission testing both motors.   Right   

      If the 383 dyno'd at say 350HP, then dyno'd at 275HP on a chassis dyno that's a 75HP loss. 
Now take the 440 and say it dyno'd at 500HP, put it in the same chassis the 383 was in and it should dyno with the same 75HP loss at 425HP.   Correct?   

How does time factor in? The 440 can do it in less time. Is that why we see the driveline losses greater on a stronger engine?

Dyno sheets show the x and y as hp/tq and rpm on a graph. It doesnt show time. What would happen if both engines were held at a steady rpm? Can hp/tq even be measured that way? Would then at a fixed rpm the driveline loss be equal for both engines? What about 2500RPM? Would driveline loss be less at lower RPM?