Dyno Accuracy
Thread Starter
Safety Car
Joined: Nov 2000
Posts: 4,419
Likes: 6
From: Arroyo Grande CA
Dyno Accuracy
First, I have absolutely no experience with a dyno.
I've seen claims where a product will add hp, as low as 2hp. Is a dyno really this accurate? If you put your car on a dyno for a pull, then immediately do a second pull. with no changes being made, will the #'s be identical between the 2 pulls? If it is, then a 2hp gain may seem reasonable to measure.
It just doesn't seem reasonable to me. Please straighten me out on this.
Thanks.
[Modified by 2KFRC5, 12:31 PM 1/17/2002]
I've seen claims where a product will add hp, as low as 2hp. Is a dyno really this accurate? If you put your car on a dyno for a pull, then immediately do a second pull. with no changes being made, will the #'s be identical between the 2 pulls? If it is, then a 2hp gain may seem reasonable to measure.
It just doesn't seem reasonable to me. Please straighten me out on this.
Thanks.
[Modified by 2KFRC5, 12:31 PM 1/17/2002]
Le Mans Master
Joined: Nov 2000
Posts: 7,294
Likes: 1
From: Coral Springs Florida
Re: Dyno Accuracy (2KFRC5)
This is a really loaded question!! You will get some controversy with this one. :rolleyes:
I can only relay my experiences with the dyno.I've had the car dynoed by Breathless Performance twice now (about 10 pulls)and that is my only frame of reference.He uses a Mustang Dyno..it's portable and supposedly very accurate. The last time I dynoed the car on Jan 7 we made 6 pulls to verify the #'s.The pulls were all pretty close.The weather has a little to do with it to. The drier less humid air will have an effect on the #'s as well as the temperature.The temperature of the engine will also be a factor.
Because I am a perfectionist by nature ,I will get the car dynoed by another shop with a Dyno Jet.This to validate and support the Mustang dyno #'s but more importantly to get the air/fuel rates so that I can fine tune the car with Steve Cole of TTS powersystems. My guess is unless we are under the absolutely same enviromental circumstances the #'s may be different.
That being said, No...dynos will be different in most situations. There are too many variables.Close...maybe, but never exact.:D
I can only relay my experiences with the dyno.I've had the car dynoed by Breathless Performance twice now (about 10 pulls)and that is my only frame of reference.He uses a Mustang Dyno..it's portable and supposedly very accurate. The last time I dynoed the car on Jan 7 we made 6 pulls to verify the #'s.The pulls were all pretty close.The weather has a little to do with it to. The drier less humid air will have an effect on the #'s as well as the temperature.The temperature of the engine will also be a factor.
Because I am a perfectionist by nature ,I will get the car dynoed by another shop with a Dyno Jet.This to validate and support the Mustang dyno #'s but more importantly to get the air/fuel rates so that I can fine tune the car with Steve Cole of TTS powersystems. My guess is unless we are under the absolutely same enviromental circumstances the #'s may be different.
That being said, No...dynos will be different in most situations. There are too many variables.Close...maybe, but never exact.:D
Le Mans Master
Joined: Aug 2000
Posts: 5,529
Likes: 1,941
From: Austin Texas
Re: Dyno Accuracy (2KFRC5)
A dyno has two numbers you should understand: one is accuracy, the other is precision.
Given that you car is not changed between runs (oil and water temperature included) a dyno should display 1% level of accuracy and 2% of precision. This means that any set of runs should be within 3HP, and that the HP resulting should be within 6 HP of 33,000 lb-ft/min reference standard.
On top of the accuracy and precision of the dyno are the pressure of air, the temperature of the air, the reletive humidity of the air. There are equations to convert a run at one set of air-metrics to a standard metric. So dyno numbers are generally specified reletive to standard temperature, pressure, and reletive humidity. This is the corrected number.
Finally, the water temperature, oil temperature (in the engine, tranny, and differential) can infulence the results. Many dyno runs are better on the second runs because of the oil is fully up to temperature but the water is not overly hot (yet).
A very careful set of dyno runs can separate a 2 HP gain. A typical 10 minute session on a dyno cannot. 5 HP yes, 2 HP no.
Given that you car is not changed between runs (oil and water temperature included) a dyno should display 1% level of accuracy and 2% of precision. This means that any set of runs should be within 3HP, and that the HP resulting should be within 6 HP of 33,000 lb-ft/min reference standard.
On top of the accuracy and precision of the dyno are the pressure of air, the temperature of the air, the reletive humidity of the air. There are equations to convert a run at one set of air-metrics to a standard metric. So dyno numbers are generally specified reletive to standard temperature, pressure, and reletive humidity. This is the corrected number.
Finally, the water temperature, oil temperature (in the engine, tranny, and differential) can infulence the results. Many dyno runs are better on the second runs because of the oil is fully up to temperature but the water is not overly hot (yet).
A very careful set of dyno runs can separate a 2 HP gain. A typical 10 minute session on a dyno cannot. 5 HP yes, 2 HP no.
Melting Slicks
Joined: Jun 2001
Posts: 2,123
Likes: 0
From: Stockton CA
Re: Dyno Accuracy (MitchAlsup)
Also you need to ask how the dyno is calibrated. Some dynos have the Watts / HP ratio off a little (white produces higher numbers than in reality)
Typically they will use the 700 Watt - 1hp ratio. In order for you to get accurate results it should be 746 Watts - 1hp.
Typically they will use the 700 Watt - 1hp ratio. In order for you to get accurate results it should be 746 Watts - 1hp.
Thread Starter
Safety Car
Joined: Nov 2000
Posts: 4,419
Likes: 6
From: Arroyo Grande CA
Re: Dyno Accuracy (MitchellDavidson)
Thanks guys.
Now, from the way I understand what all was said, is that if all fluid temps, atmospheric conditions, and any other conditions could be duplicated, including the way the calculations are made, then the runs should be within 1%. So, realistically, a 3hp error could still occur on a 300hp car.
Rhill, now that would earn you Bragging Rights! :lol: :lol:
Now, from the way I understand what all was said, is that if all fluid temps, atmospheric conditions, and any other conditions could be duplicated, including the way the calculations are made, then the runs should be within 1%. So, realistically, a 3hp error could still occur on a 300hp car.
Rhill, now that would earn you Bragging Rights! :lol: :lol:
Thread Starter
Safety Car
Joined: Nov 2000
Posts: 4,419
Likes: 6
From: Arroyo Grande CA
Re: Dyno Accuracy (wallstAL)
I'll pass on this one!
Thanks again!
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Race Director
Joined: Oct 1999
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From: Arlington TX
Re: Dyno Accuracy (2KFRC5)
Most of these dyno (if not all) being inertial type (spinning a known weight measuring the angular acceleration from which torque is calculated) dynos even changing your wheels will change the horsepower. If wheels are swapped for lighter ones and everything else being the same your hp will increase according to the dyno.