Dyno questions

Rohan,
'And you have all the race wins to back this statement up ?
This would be interesting to explore on a dyno, wouldn't it....'

My racing history mainly involved campaigning an old Triumph 500 twin in Allpowers C Grade against big two strokes and four cylinder superbikes, the bike was fairly trick so I was still competitive. However from all that wasted effort and bullshit, I actually learned a few things.I built my Seeley 850 back in the early 80s, and because I was horrified at what was in the motor I never raced it until fairly recently . I think my record of wins could have been considerably better had I actually believed in the piece of garbage. As I said, never predict outcomes when developing your bike. I believe a dyno is a useful tool in the right hands, the info it delivers can set a base line for the next step, if the improvement works on the track.
 
Tex, wouldn't it be more sensible to put the bike of the dyno to load it, then measure the forward thrust with a load cell, as the motor comes up through the rev range ? You could then relate this to the BHP measurements.
 
texasSlick said:
to dances with schrapnal

the dyno measures power. a load cell measures force. torque is force acting over a distance.
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Force acting over a distance is called WORK (force X distance), not TORQUE. The rate or speed in which the work is done is used to calculate POWER.

I think the distance you are referring to is the lever arm distance, correct? And how would you measure the force acting on the end of that lever arm - one way would be by using a load cell. Thus force acting on a lever arm of X length yields a TORQUE.

To be concise, a brake dyno registers (measures) force and speed and calculates torque and power. An inertial dyno measures speed and acceleration of a known rotational mass and calculates torque and power.
 
when you say "makes more sense" what exactly are you trying to accomplish? the dyno can give you the effects of making a tuning change....if some change gives you more hp at some rpm, then you will be getting more torque, and thus more acceleration at that rpm will result once unfettered from the dyno.
 
Re: Dyno questionsqq

to dances....

work is force x distance....but the distance is a displacement distance. torque is force acting over a distance...no displacement is required.. both work and torque have the same units....eg. ft pounds, or newton meters.

power is the time rate of doing work....= work/time

a load cell measures force....if that cell, loaded with a force F, were placed a certain distance from a point, there would be a torque at that point = F x distance. This arrangement is not how engine torque can be computed, as the torque so computed is as much a matter of the distance selected (arbitrarily) as the force generated by the device creating the force on the load cell.

I maintain a dyno measures power, from which torque is computed. I am not familiar with inertial dynos, but from your description, I would agree if acceleration of a rotational mass is being measured, the dyno is not measuring power but torque, from which hp can be computed. the equation given can be solved either way.
 
Re: Dyno questionsqq

texasSlick said:
to dances....

a load cell measures force....if that cell, loaded with a force F, were placed a certain distance from a point, there would be a torque at that point = F x distance.
Click to expand...

so far so good, you see what I see. But below is where it falls apart.

texasSlick said:
This arrangement is not how engine torque can be computed, as the torque so computed is as much a matter of the distance selected (arbitrarily) as the force generated by the device creating the force on the load cell.
Click to expand...

The leverage arm can be selected arbitrarily in a brake dyno; it is just a matter of multiplying whatever arbitrary arm distance by the force (measured by load cell for example) equals TORQUE. Nothing arbitrary about that.

texasSlick said:
I maintain a dyno measures power, from which torque is computed.
Click to expand...

I suppose some dynos are simply a generator (with a backfed EMF) being driven by the test engine (bike) where instead of physical forces you are reading volts and amps but volts and amps are proxies for (force) and (force X distance); same may be said about an eddy brake where the measured EMF at a given speed can be used to calculate torque & power. I think the problem there is the heat generated causes drift. I suppose some water brake dynos used water pressure and water flow rate as the proxies for (force) and (force X distance).

texasSlick said:
I am not familiar with inertial dynos, but from your description, I would agree if acceleration of a rotational mass is being measured, the dyno is not measuring power but torque, from which hp can be computed. the equation given can be solved either way.
Click to expand...

I do not believe there is a device in the world that can make a direct measure of power. Dynos rely on a few measurements to compute (calculate) power.
 
volts x amps = watts = power. the dyno measures and controls volts and amps to dissipate the engine's power. it is called brake hp because the dyno is a dynamic brake holding the engine rpm constant at full throttle.


IF an engine's power were dissipated by, let's say, an oil or water pump, and IF the engine were mounted on a special test stand that would allow the engine and stand to rotate counter to the normal engine rotation, and IF a lever were attached to the stand preventing such rotation, and IF the lever were attached to a load cell....you are right....torque would be measured and hp could be computed. Such a setup might work in a test laboratory, but not practical for testing the hp of a vehicle coming in off the street.

this is my last post on this topic.
 
For those interested in understanding a little more about brake dynos (absorbing dynos) I draw your attention to the image below; in particular, items 4 and 5 where item 4 is typically a load cell. Tada! No "IF"' about it.

Dyno questions


Digging into it a bit you can read and compare and contrast the different types of absorbing (brake) dynos.

https://en.wikipedia.org/wiki/Dynamometer

Some examples include eddy brake, magnetic powder, water turbines etc.

This may be my last post on this topic.
 
Rohan, As I said I'm ignorant about the intricacies of modern dynos. However from what I've read, the responsive exhaust gas analyser in common use measures oxygen content. How does that determine that the mixture burnt in the combustion chamber is stoichiometric ? Seems to me stochiometry varies with the chemical composition of the fuel. Do you believe that the oxygen content of the gas from a stoichiometric mixture of air and methanol burning , is the same as that from ordinary petrol or avgas which has a lot of highly branched hydrocarbons as well as lead? But what would I know ?

My feeling is that dynos are good for measuring one condition - full throttle at max revs. A condition which is not used as much as many might believe on a race bike unless, or even if your riding style is always 'point and squirt'. At every other time we are dealing with partial throttle openings, and varying revs and gear ratios - looking for midrange power.
 
Combat, your efforts on the BMW sound really great. If you are outriding the opposition you are more than halfway to winning. Give it a big dose of nitro or fit a replica Zoller blower and paint it black. Alternatively you could wind the rubber band up tighter.
 
acotrel said:
However from what I've read, the responsive exhaust gas analyser in common use measures oxygen content. How does that determine that the mixture burnt in the combustion chamber is stoichiometric ?
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Good question but it does work and that is what counts. One little note her is that it reports air/fuel ratio, not stoichiometric anything.


acotrel said:
Seems to me stochiometry varies with the chemical composition of the fuel. Do you believe that the oxygen content of the gas from a stoichiometric mixture of air and methanol burning , is the same as that from ordinary petrol or avgas which has a lot of highly branched hydrocarbons as well as lead? But what would I know ?
Click to expand...

You bring up an interesting point. Maybe there's a calibration for methanol use.

acotrel said:
My feeling is that dynos are good for measuring one condition - full throttle at max revs. A condition which is not used as much as many might believe on a race bike unless, or even if your riding style is always 'point and squirt'. At every other time we are dealing with partial throttle openings, and varying revs and gear ratios - looking for midrange power.
Click to expand...

This is where you are missing it. With a brake dyno you can vary throttle position and map power, torque and air/fuel ratios across a span of throttle openings for a given rpm. This is valuable information especially if you are looking for best power and drive out of corners. Much of this information can also be gained with an inertial dyno.

Also, if you significantly change an engine (compression, valve timing, intake and exhaust tract tuning etc. you can see where ignition timing will give you best power.

Your feeling about dynos only being good for WOT full revs is in my opinion, missing a lot.
 
Dances with Shrapnel said:
acotrel said:
Seems to me stochiometry varies with the chemical composition of the fuel. Do you believe that the oxygen content of the gas from a stoichiometric mixture of air and methanol burning , is the same as that from ordinary petrol or avgas which has a lot of highly branched hydrocarbons as well as lead? But what would I know ?
Click to expand...

You bring up an interesting point. Maybe there's a calibration for methanol use.
.
Click to expand...

Of course there is.
There are different fuel-air ratios for every fuel - methanol, ethanol, petrol, kerosene, diesel, lpg, coal gas, powdered coal, fueloil, etc.

I think methanol is about 6:1, ethanol is 8:1, petrol is about 14.7:1, etc etc

Note that aiming for perfect combustion is like chasing the holy grail.
In an ideal world, it might happen.
In an internal combustion engine, never....
So, like everything, its a compromise.
 
Rohan said:
Dances with Shrapnel said:
acotrel said:
Seems to me stochiometry varies with the chemical composition of the fuel. Do you believe that the oxygen content of the gas from a stoichiometric mixture of air and methanol burning , is the same as that from ordinary petrol or avgas which has a lot of highly branched hydrocarbons as well as lead? But what would I know ?
Click to expand...

You bring up an interesting point. Maybe there's a calibration for methanol use.
.
Click to expand...

Of course there is.
There are different fuel-air ratios for every fuel - methanol, ethanol, petrol, kerosene, diesel, lpg, coal gas, powdered coal, fueloil, etc.

I think methanol is about 6:1, ethanol is 8:1, petrol is about 14.7:1, etc etc
Click to expand...

I think the question posed is will an A/F ratio be correctly presented on the monitoring device if using Methanol? I don't know how the A/F reading is made but let us accept for this discussion that it reads % oxygen only, it must assume it is gasoline and then calculates the A/F based on oxygen depletion? I believe the ratio is (unit mass)/(unit mass). Furthermore I read here and there that alcohol in fuel has knackered up oxygen sensors on cars so maybe Methanol is a special case. Maybe this is part of acotrel's concerns.
 
Dances with Shrapnel said:
Your feeling about dynos only being good for WOT full revs is in my opinion, missing a lot.
Click to expand...

Yes.
If the dyno is equipped with a brake - electrical, water, wind vane, friction material, whatever,
then you dial up the required revs, increase the load, and measure what the engine will produce.
And measure the exhaust gases, to see what you are missing...

Fuel injection does a part of this, on the fly, as you ride down the road.
Thats how they get the fuel use so low, and the power so high - in the sophisticated ones anyway...
 
Dances with Shrapnel said:
I think the question posed is will an A/F ratio be correctly presented on the monitoring device if using Methanol? I don't know how the A/F reading is made but let us accept for this discussion that it reads % oxygen only, it must assume it is gasoline and then calculates the A/F based on oxygen depletion? I believe the ratio is (unit mass)/(unit mass). Furthermore I read here and there that alcohol in fuel has knackered up oxygen sensors on cars so maybe Methanol is a special case. Maybe this is part of acotrel's concerns.
Click to expand...

Ask the dyno operator if he is familiar with methanol fuel tuning.
Its not like this stuff has just been invented....

Fuel injected cars and bikes have an O2 sensor as a primary part of their EFI, and its not like you see them abandoned by the millions along the roadsise...
 
Rohan said:
Ask the dyno operator if he is familiar with methanol fuel tuning.
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No shit. :roll:

It would be a logical thing for acotrel to do.

Rohan said:
Fuel injected cars and bikes have an O2 sensor as a primary part of their EFI, and its not like you see them abandoned by the millions along the roadsise...
Click to expand...

Of course they don't run Methanol, do they? It was just a question Rohan, not a statement of fact.
 
There is so much woolly thinking quoted in some of these threads,
its good to separate some of the wheat from the chaff.... ?
 
I've got a couple of questions. I suggest the rod length affects torque in two ways. If the rod is longer, the angularity is adversely affected, but the rock-over time is extended, so the time duration of the fuel burn probably has to be compatible with the rod length, and the inlet port diameter at various revs. Obviously whatever motor configuration is chosen, if the dyno is sensitive enough, the optimum ignition timing and main jet can be found, however how do you then adjust the mid-throttle jetting so that the output is the maximum which suits your gearing for various circuits ? I'm still thinking about the Mikuni needles which have three stage tapers. How do the MX guys decide which to use for max benefit ?
 
A comment that Rohan made is relevant. You can run methanol rich and still get good power, however from long experience I know that it is best run as lean as possible right down the needle. The Mikuni needles give a better opportunity to find the optimum taper so that when accelerating out of and around corners , you are getting the max regardless of throttle opening. It is important if you are trying to outride others on the tight stuff. Leaning off the midrange when using methanol does not affect reliability of four stroke motors, the blow-ups come at the ends of long straights if the mains are too lean or the needles obstruct the mains. On two strokes they often happen as you shut off. I believe the reason that Amal X and Y alcohol needles are so pointy is to avoid the situation where the motor never runs on the mains. This can be overcome by slightly recessing the needle jet so that the tip of the needle is always captured, however never obstructs. This slightly moves the metering position of the needle.
 
acotrel said:
I've got a couple of questions. I suggest the rod length affects torque in two ways. If the rod is longer, the angularity is adversely affected, but the rock-over time is extended, so the time duration of the fuel burn probably has to be compatible with the rod length, and the inlet port diameter at various revs.
Click to expand...

Guys on Chev forums debate this endlessly, ad nauseum.
Keeps them safe and off the streets anyway...

As Phil irving said, the combustion pressures can only do so much work, and how it delivers it can can in different forms with different rods.
So you pays your money and takes your choice....
 
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