Dyno Truths

BRUTAL64

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Some interesting reading::bounce:

"Dyno Torque Figures – the truth.


On the styles of Chassis Dyno's we see here in Australia, for example a Mainline Dynolog or a Dyno Dynamics, both of these dyno's, calculate power at the roller in the same fashion. That is, we measure Roller RPM and Roller Torque and these 2 variables are used in the traditional Power calculation formula, either metric or imperial, you get the same result:

HP (@ roller) = (roller torque ft/lbs x roller rpm)/5252

Or

kW (@ roller) = (roller torque Nm x roller rpm)/9543

When the term Roller Torque is used, this means we are measuring Torque from a Load Cell that is attached in some fashion to the Retarder (Eddy Current Retarder/PAU) that is coupled to the Drive Rollers (the knurled rollers). The Retarder applies a braking force to the Rollers, and since the Retarder Frame is restrained from turning by the Load Cell, the force is transferred into the Load Cell which measures force in typically Kg or Pounds force. The length of the arm the Load Cell is attached to is precisely known, so with force over a given length we can determine Nm or Ft/lbs.

Roller RPM is usually measured by an Inductive speed sensor of some type, or a Shaft Encoder, or in the old days on a Vane Dyno, a Tacho generator.

These 2 inputs are used by the Dynamometer Control System to calculate the Power.

Now, because we measure Torque down in the Dyno bed from a device that is coupled to the Roller, ANY gear multiplication, or gear reduction, will influence the Torque measured at the Roller. So some variances that come into the equation are:

Torque Converter slip ratio
Transmission ratio
Differential ratio
Tyre size
Roller size

These variables all influence the Torque as measured at the roller.

Some people will then initially think, the lower the gear, the more Torque, so the more Power we will make, THIS IS NOT TRUE.

Remember the formula for calculating Power, we have Torque AND RPM, so if we use a lower gear ratio, the corresponding RPM will be reduced by the same factor as the Torque is increased, so we end up with the same power. This is a purely mathematical explanation.
The reason some of the confusion happens in regards to Torque (roller torque) on a Chassis Dyno, is there are 2 common sizes of rollers used on dyno's here in Australia, those being 219mm or 273mm (these are raw, unmachined sizes).

The larger diameter roller will have a higher Torque reading at a given Road Speed, but have a corresponding lower RPM, the torque value increase will be the difference in Roller Diameter, I've done the maths for you, the 273mm roller will have 24.6% more torque. What this means is, a particular car may have 200RWKW, but it may have 500Nm on a 219mm roller, but 623Nm on a 273mm roller.

We now need to understand the Torque that gets to the roller, and why it is normally higher than at the Crank. Remember I listed all the things that will influence the Torque at the Roller, Gearbox Ratio, Diff Ratio, Tyre size etc. If I simplify it somewhat, we'll use a gearbox ratio of 1:1 in the following example, I also am not accounting for driveline loss in this example.

Take a traditional LS1, a torque figure of 530Nm is quoted at the crank. If the Gearbox Ratio is 1:1, so we have 530Nm going into the diff, now if we have a diff ratio of 3.46:1 (this is a gear multiplication), we then have 1833Nm at the axles. (Those that have had their cars dyno'd on a Dyna Pack Hub Dyno will be accustomed to these numbers). The next step in the Torque journey is the Tyre to Roller ratio.
This is where the Dyno Roller size will affect this value. If we transfer the 1833 axle Nm thru a 650mm tyre to a 219mm roller (this is now a Gear Reduction), this ratio is 1:2.968, so we divide our 1833 by 2.968, gives us 617.58Nm on a 219mm Roller.
In the case of a 273mm Roller, our ratio is 650/273 = 2.3809, so we divide the 1833 axle Nm by 2.3809 giving us 769.87Nm roller Torque on our 273mm roller.
Remember the larger roller will be doing less rpm at a given road speed, so the same power will be present.

To simplify this somewhat, both Dyno manufacturers have a term that makes the differences in Roller sizes a non issue, this term is Motive Force on a Mainline Dynolog, or Tractive effort on a Dyno Dynamics. Motive Force/Tractive Effort is a Calculation (this is where some dyno operators get it wrong, they believe the dyno measures Tractive effort).
Motive Force/Tractive Effort is calculated as such, Roller Torque/Roller Radius, so in our example above, we have 617.58Nm/0.1095metres (radius or 219mm roller) giving us 5640 Newtons (not Newton Metres, Newtons are a linear force, Newton Metres are a twisting Force). On our large roller, we have 769.87Nm/0.1365 giving us 5640 Newtons.

Putting this into context for this thread, APS Service Centre's dyno has 273mm rollers, so their Roller Torque figures will be approx 24.6% higher than say Sonny's dyno, because Sonny has 219mm Rollers in his dyno, but both dyno's would show the same Power and Motive Force.

In order to simplfy the Torque values even further, both Dyno Manufactures have what we term "Derived Torque", which is a calculated value based of RWKW and Engine RPM, this calculated "Derived Torque" takes any gear multiplication out of the equation, so one very good way of using Derived Torque is, if you have a particular car that had 3.46 diff gears, and has now been changed to 3.7, the Derived Torque value will not be affected, whereas the Roller Torque will, due to the fact the overall gearing of the car has changed.

Derived Torque numbers will be basically your Engine Torque minus Driveline Torque loss, so owners of cars who get a Dyno Printout can more easily come to terms with Derived torque, as they accept that Torque at the wheels will be lower than at the engine, (Derived Torque is a bit of window dressing, or dumbing it down).

On a Mainline Dynolog, the user has 3 available RPM signals available to the software for it to Calculate the Derived Torque, Tacho RPM (ie HT lead, injector trigger etc), OBDII Tacho RPM, or lastly Derived RPM from the Roller Speed. The first 2 options will provide very accurate Derived Torque values, whereas using Derived RPM (which is based on a ratio of vehicle dashboard tacho against roller speed), will not be very accurate on a Automatic car due to the varying slip ratio of a torque convertor, but will be accurate at whatever point the Derived RPM figure was set. Dyno Dynamics also have a version of Derived Torque, I believe it is just called RWNm or just Torque Nm on a Graph when printed, I'm also led to believe that the DD version also only uses a derived RPM number for the Derived Torque, not an actual true Engine RPM value, but I could be wrong, and if someone can clarify this, I'm happy to be corrected.

While I suggest to users of our system to use Derived Torque on Reports given to customers, they can do as they please, and a lot just use Roller Torque. It only takes a few seconds to choose to display Derived Torque. All of our reports do report Motive Force though, so for a comparative point of view to a Dyno Dynamics Graph, compare the Tractive Effort to Motive Force on a Mainline Dynolog.

Now a something to remember, the Motive Force or Torque, has the exact same shape curve when compared on a similar Graph Scale.

Another benefit of displaying Derived Torque, if you are a Horsepower and Foot Pounds of Torque junky, instead of kW and Nm, the Derived Torque and Horsepower will cross at 5252rpm, (just like it does on an Engine Dyno)."

Taken from LS1.com

You guys (you know who you are) didn't think I was going to leave this alone.:bump:
 
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Interesting reading..

And I had a thought- I wonder if that plug boot was arcing Saturday and I hadn't noticed it at that point. Do you think that could have upset the RPM signal to the dyno?
 
Interesting reading..

And I had a thought- I wonder if that plug boot was arcing Saturday and I hadn't noticed it at that point. Do you think that could have upset the RPM signal to the dyno?

Yes, that is one thought I had. Not sure how yet, but I'm giving it some thought between phone calls.:drink:
 
Yes, that is one thought I had. Not sure how yet, but I'm giving it some thought between phone calls.:drink:

OK, put this in your hat too- remember how they couldn't get John's car to give up a tach signal with the shielded wires? Not enough EMI around the wire to pickup. Now I've got a wire that's leaking (arcing) way too much noise. Put that on and spin it.:idea:
 
Hey Tim:

Another benefit of displaying Derived Torque, if you are a Horsepower and Foot Pounds of Torque junky, instead of kW and Nm, the Derived Torque and Horsepower will cross at 5252rpm, (just like it does on an Engine Dyno)."

Think I'll get a gold star? I stated this on DC.:quote:
 
OK, put this in your hat too- remember how they couldn't get John's car to give up a tach signal with the shielded wires? Not enough EMI around the wire to pickup. Now I've got a wire that's leaking (arcing) way too much noise. Put that on and spin it.:idea:


Hell, you really want me to think, don't you.:lol:


But, the problem with John's engine readings did come to mind. Where it goes from there I'm not sure.:flash:
 
After reading your IP, I got to thinking about the whole show again. They couldn't get a good read on John's car not enough EMI around the wires for the tach. It makes sense to me that with my wire(s) leaking they got too much. That would seem to me a good reason that both the curves looked like they were in the middle of an earthquake. Instead of reading an RPM signal on one wire as it should, it's getting readings from 2 and got really confused.
 
After reading your IP, I got to thinking about the whole show again. They couldn't get a good read on John's car not enough EMI around the wires for the tach. It makes sense to me that with my wire(s) leaking they got too much. That would seem to me a good reason that both the curves looked like they were in the middle of an earthquake. Instead of reading an RPM signal on one wire as it should, it's getting readings from 2 and got really confused.

Yea, That may be the case. EMI, if enough, can actually fire the plug wire close to it (one of the biggest problems with 5 and 7). It is possible ,but not likley, that you were arcing in the cap.

I think it was an equipment ( dyno) problem of some sort. Since it showed up on more than one vehicle. Still need to give it more thought. Need to look at your dyno graph again.:search:
 
After reading your IP, I got to thinking about the whole show again. They couldn't get a good read on John's car not enough EMI around the wires for the tach. It makes sense to me that with my wire(s) leaking they got too much. That would seem to me a good reason that both the curves looked like they were in the middle of an earthquake. Instead of reading an RPM signal on one wire as it should, it's getting readings from 2 and got really confused.

Are you going to dyno again at a local place?
 
I have been thinking about getting another dyno run. kwplot34 (Kevin) has found a place not too far from us. I need to get rid of the mixed gas first and get a good load of 110 back in there. The way that thing uses gas, it won't take too long. And a couple of things I want to do- one is get the 850 Demon carb all setup so a swap is a quick easy thing, and then I need to do some maintenance stuff- oil change, check timing, look at the plugs and wires and adjust the valves.

I want to go back on the dyno with the same stuff I had the frst time- no good in making any changes and then going. That proves nothing. But then I also want to swap carbs and go again- see what the difference is between the Holley 750 and the Demon 850 in real numbers. I've got a Weiand Team G open plenum intake there too, but I need a taller hood. Or I could get real busy and put the Edelbrock 2x4 back on there. And it fits under the hood.
 
I have been thinking about getting another dyno run. kwplot34 (Kevin) has found a place not too far from us. I need to get rid of the mixed gas first and get a good load of 110 back in there. The way that thing uses gas, it won't take too long. And a couple of things I want to do- one is get the 850 Demon carb all setup so a swap is a quick easy thing, and then I need to do some maintenance stuff- oil change, check timing, look at the plugs and wires and adjust the valves.

I want to go back on the dyno with the same stuff I had the frst time- no good in making any changes and then going. That proves nothing. But then I also want to swap carbs and go again- see what the difference is between the Holley 750 and the Demon 850 in real numbers. I've got a Weiand Team G open plenum intake there too, but I need a taller hood. Or I could get real busy and put the Edelbrock 2x4 back on there. And it fits under the hood.



I like dual quads:friends:, yes I do.:drink:

I even get BETTER gas milage with 2 500s that I did with one 650 dual feed Holley.:shocking:
 
sounds like just playing games with numbers.

x torque times y rate = xy hp
(1/2)x torque times 2y rate = xy hp
so on and so forth.

it boils down to force x speed. the only thing that has always bothered me is that a dyno run is so quick that it doesn't allow for steady state measurement, ie the wheels are accelerating a mass all the way through the rpm band. I guess they know the mass of the machine and take that into account.
 
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sounds like just playing games with numbers.

x torque times y rate = xy hp
(1/2)x torque times 2y rate = xy hp
so on and so forth.

it boils down to force x speed. the only thing that has always bothered me is that a dyno run is so quick that it doesn't allow for steady state measurement, ie the wheels are accelerating a mass all the way through the rpm band. I guess they know the mass of the machine and take that into account.

It's always been a numbers game.:D
 
Everything is a numbers game. There's a percentage (number) of people that will go to bed tonight and won't get up tomorrow.
 
derrived torque, Tractive Effort, Motive Force, blah blah blah,



it's sorta like asking what is heavier. A pound of lead or a pound of feathers.

Any asshole know the answer to THAT, the pound of lead, obviously...


sneeze on a pound of lead, what you have??? wet lead.....


sneeze on a pound of feathers, what you have??? a huge clean up job...




CASE CLOSED.....


damn engneers allways gotta make simple shit complicated....

jeez....

:bonkers::flash::yahoo:
 
does a chassis dyno have a barometric pressure adjustment? I have no experience with a chassis dyno and very little with an engine dyno but I do know if you twist the dial that adjusts for barometric pressure "just right" you can make the numbers read whatever you like, hence the term "happy dyno"......You really shouldn`t consider any type of dyno anything more than a tuning tool, the number isn`t whats important, whats important is the change in the number you see after making a tuning change to your car/engine...also important is to compare apples to apples, all dynos are different so going back to the same place (same dyno) gives consistent results.
redvetracr
 
does a chassis dyno have a barometric pressure adjustment? I have no experience with a chassis dyno and very little with an engine dyno but I do know if you twist the dial that adjusts for barometric pressure "just right" you can make the numbers read whatever you like, hence the term "happy dyno"......You really shouldn`t consider any type of dyno anything more than a tuning tool, the number isn`t whats important, whats important is the change in the number you see after making a tuning change to your car/engine...also important is to compare apples to apples, all dynos are different so going back to the same place (same dyno) gives consistent results.
redvetracr

Friend of mine with a nicely built small block camaro dynoed his engine before installing it. Had a nice couple of runs around 430hp. He then showed me a "corrected" (don't recall the exact termonology he used) graph for elevation/pressure, etc. The corrected graph showed about 450hp. Guess you can make the results what you want.
 
sounds like just playing games with numbers.

x torque times y rate = xy hp
(1/2)x torque times 2y rate = xy hp
so on and so forth.

it boils down to force x speed. the only thing that has always bothered me is that a dyno run is so quick that it doesn't allow for steady state measurement, ie the wheels are accelerating a mass all the way through the rpm band. I guess they know the mass of the machine and take that into account.



Yep HP is a function of Torque...

You get slip too... The 120HP two stroke bikes hit so hard when come on the pipe that they spin the wheel against the drum until you get the tire up to temp. Even with fancy contollers and variable exhaust ports to soften the hit.

Our new MC dyno has load control so you can get steady state and build custom fuel maps.

I'm guessing that up to date car chassis dyno's have the same capability.

I also agree that the magnitude of the numbers is not the most important thing for tuning its the progress against the baseline and the consistency in the setup.

:thumbs:
 
does a chassis dyno have a barometric pressure adjustment? I have no experience with a chassis dyno and very little with an engine dyno but I do know if you twist the dial that adjusts for barometric pressure "just right" you can make the numbers read whatever you like, hence the term "happy dyno"......You really shouldn`t consider any type of dyno anything more than a tuning tool, the number isn`t whats important, whats important is the change in the number you see after making a tuning change to your car/engine...also important is to compare apples to apples, all dynos are different so going back to the same place (same dyno) gives consistent results.
redvetracr


Its a tool !! I agree...

To compare results needs to be calibrated and corrected to standard pressure temp and humidity... I forget it's something like 29.92" Hg, 70*F ?? humidity

The weather station to plug into the dyno was $1300 Pressure, temp, humidity...
 
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