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Discussion Starter · #1 · (Edited)
DYNO and how it works.

READ THIS ^^^^ Its what ive been trying to say....just dont have enough time to put it in writing like the above author did!!!!

This link is pulled from this very website....

The only thing that is not up to date in this specific link is the fact that the new dynojet that [email protected] is using is a bit more sophisticated than the current desription of the "torque measurement"....

The software in the DynoJet224xlc that CRAIG was on uses its own calculations that we DONT KNOW...(secret stuff) in measuring HP. Its a formula that is based off a calibrated test from the factory to achieve its HP number...hence the no RPM.


As for the dynojet 248 that everyone is familiar with....

You absolutely do not need a RPM input to achieve a HP number. It is based off its own "dynojet" formula based off the drum weight.

Ken White, yes you are correct in the fact that they do use mass-force to calculate a HP number but there is no REAL torque reading on a Dynojet or Mustang dyno......With the exception of the dynojet224xLc that is newish to the market.

I hope this helps.

Reguards
JustinM.
(feel free to correct me where im wrong, im not scared, nor do I wear my feelings on the internet LMAO)
 

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Ken White, yes you are correct in the fact that they do use mass-force to calculate a HP number but there is no REAL torque reading on a Dynojet or Mustang dyno......With the exception of the dynojet224xLc that is newish to the market.
CatDiezel, the only connection you are missing is that torque is rotational force applied by the tires to the dyno drum, which by the way is equal and opposite - we can only measure rotational acceleration or rotational force.

If the dyno measures force instead of acceleration, then the calculation must use torque for the calculation.

Torque = Tangential Force x Lever Length (Drum Radius)

If the dyno measures acceleration, then the drums acceleration is used to calculate torque.

Torque = mass drum x radius drum x acceleration drum

Horse Power is a derived quantity that is the rate of energy transfer and cannot be measured directly as far as I know.

:)

EDIT: I agree discussions back and forth are great to help with understanding...
 

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Discussion Starter · #3 ·
Ken, to put it simple.... I agree with you....

I guess we can call the dynojet and mustang dyno and accelerometer than LOL. Because its calculations are measured from "how fast can you turn the drum, with knowing what the drum weight is" !!

A mustang dyno is even worse IMO, your allowed to alter WAY too much input forr the fantasy HP number. Such as entering truck weight and temp. The beauty of te dynojet is that it does not care about your vehicles weight. And it has its own weather station for corrected numbers!! LOL..... Everything should be uncorrected IMO.
 

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I agree, the only valid torque or HP numbers are the ones measured at the wheels and even these don't really mean much without knowing at what rpm they occur. Corrected numbers are just and educated guess based on a mathematical model of one system...

:thumbsup:
 

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Discussion Starter · #5 ·
I agree, the only valid torque or HP numbers are the ones measured at the wheels and even these don't really mean much without knowing at what rpm they occur. Corrected numbers are just and educated guess based on a mathematical model of one system...

:thumbsup:
Folks get off on their dyno sheet because at the bottom, even though its a HP only graph, it represents MPH. Given that you can have a good fealing for what is going on....sort of LOL....

Track times dont lie!!!!... And the calculators for track times are VERY accurate.
 

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You guys obviously know more about this subject than i do.

The reason i started all of this yesterday , as the fact that Craig said "The RPM sensor was broken so all i got was my HP." (words to that effect)

And that went against what I have learned about dyno's.

that is they measure your RPM and torque, and then do the math and give you your HP.

And like the thread links I sent you Cat, everything I see on the Net supports that.

Google "does a dyno measure torque or HP?" And look at all that comes up, almost everyone of them says "Dynos measure trq and RPM and Calculate HP."

Now I understand what Cat has been trying to say. He has been referring to Watts observation that a Horse can move 550 lbs so many feet in 60 seconds. and basically that is what Craig's dyno was doing. It had weighted wheels that were being spun and accelerated a certain amount in a measured amount of time. Giving HP.

But that does not seem as accurate or real as actually measuring the twisting force of the wheels (trq) and the RPM.

I put an e-mail into Dynojet, I am waiting to see what they have to say. I kept it simple and direct.

Hello,

Please help me with a simple question. (I hope)

Everything I have found on the internet tells me that a dyno (automotive) measures torque and engine RPM, then gives you HP based on....

HP = (Trq X rpm) / 5252

In other words the dyno is ONLY measuring Trq and engine RPM. HP is being calculated NOT measured.

Is this true?

TY

Ken S.

:)
 

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Discussion Starter · #7 ·
Ksseabrd,

Did you read the link I posted above in this thread?

Its a good read....!!! You really only need to read the first post though. If not you will be up awhile!
 

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Discussion Starter · #8 ·
Quoted.........


First it is important to have an understanding of how DynoJet gets their horsepower numbers. Power in mechanical terms is the ability to accomplish a specified amount of work in a given amount of time. By definition, one horsepower is equal to applying a 550 pound force through a distance of 1 foot in one second. In real terms, it would take 1 HP to raise a 550 pound weight up 1 foot in 1 second. So to measure horsepower, we need to know force (in pounds) and velocity (in feet per second). Dynojet's inertial dynamometer measures power according to the terms just described. It measures velocity directly by measuring the time it takes to rotate two heavy steel drums one turn. It measures force at the surface of the drum by indirectly measuring it's acceleration. Acceleration is simply the difference in velocity at the surface of the drums from one revolution to the next. The force applied to the drums is calculated from acceleration using Newton's 2nd law, Force = Mass * Acceleration. Since the mass of the drums is know and acceleration has been measured, Power (horsepower) can now be calculated. Torque is then calculated using the horsepower number: Torque = Horsepower * 5252 / RPM.

Once they have these numbers a series of correction factors are applied, some made public, some hidden as proprietary secrets. The public correction factor is the SAE correction factor. This formula assumes a mechanical efficiency of 85%. The formula used is: Where: CF= 1.18 * (29.22/Bdo) * ((Square Root(To+460)/537)) – 0.18. To = Intake air temperature in degrees F, Bdo = Dry ambient absolute barometric pressure. This correction factor is meant to predict output in varying atmospheric conditions and is a +/- 7%. The proprietary correction factor is supposed to reflect the loss of power from the crankshaft to the rear wheels.
 

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Yes, an inertia dyno. that is why I mentioned Watt's test.

And that is also where I got confused, I thought Craig was using a load dyno

It is amazing how so much info on the web does not note that difference.

I will read the rest of it later.

I can see why most people tend to prefer load dyno's.
 

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There are really only a few things that can be measured directly with a dyno.

1. Time (seconds)
2. Torque or force using a pressure sensor (strain gauge)
3. Acceleration using an accelerometer which can be integrated to generate velocity as well.
4. Drum revolutions which can give distance (circumferance x revolutions) and when coupled with time per revolution it can measure velocity.

Power (joules/second) = Force (newtons) x Velocity (meters/second) for linear motion

or

Power (joules/second) = Torque (newtons x meters) x Angular Velocity (radians/second) for rotational motion

HP and RPM's are converted from these basic SI units and equations into the british/american units we are familiar with.

While velocity as the independent variable is great for the 1/8 and 1/4 mile runs, RPM's give a better indication of the "power band" and where changes should occur within the engine modifications - this depends on whether we want to pull hard and long or go fast.
 

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Discussion Starter · #11 ·
Yes, an inertia dyno. that is why I mentioned Watt's test.

And that is also where I got confused, I thought Craig was using a load dyno

It is amazing how so much info on the web does not note that difference.

I will read the rest of it later.

I can see why most people tend to prefer load dyno's.
Craig is on a dyno thats capable of both in conjunction with a eddy's brake..
 

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Got it, if someone had said: "They are using an inertia dyno." I would have figured it out quicker. I had load dyno stuck in my head.

Thanks for the link Cat, it is a good read.

;)
 

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Discussion Starter · #13 ·
No problem!!

I should have been more clear back when we were mucking up Craigs threads that I was referring to the dynojet specifically!
 
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