What is a better dyno-Dyno Dynamics or Mustang?

[BaadVR4]

Not so. Dynos have different, selectable correction algorithms to correct for atmospheric conditions at the time of the test. Here is an excellent write up on the entire issue:

There are few standards used in the dyno world for gathering HP and TQ numbers, UNCORRECTED, SAE and STD. Uncorrected is NEVER accepted in the world of dynoing and tuning as it does not factor in any weather conditions etc. Now here is where the big debate comes...is between SAE and STD. SAE (Society of Automotive Engineers) is the MOST ACCURATE AND WIDELY ACCEPTED FORM OF MEASUREMENT when it comes to the world of dynoing. Here is some more info I have gathered between the two.....

A lot of people have been asking about SAE .vs STD Dyno numbers so I thought this would help. Most people know that showing STD numbers read higher but not many know why. SAE represents more realistic standard conditions, STD artificially boosts numbers.

Identifying Your Correction Factor:
Dynojet:
If you look at a dynojet graph in the upper right corner, you will see where it says the correction method being used. The options are SAE, STD, Uncorrected and a few not needed for discussion. You will also notice a smooth factor (up to 5) which dyno operators use to make the power curves and any other data displayed, such as AFR, seem more accurate and smooth. You will also see AFR graphs scaled DOWN to hide flaws in the curve.

MD:
A Mustang Dyno ONLY uses SAE Corrections. Smoothing can also be controlled as well as scale for the Graphical Outputs.


Overview:
Most of the stated horsepower numbers are “Corrected” values. The correction standards were developed to discount the observed horsepower readings taken at different locations and weather conditions. It is obvious that an engine builder in Colorado could not produce as much horsepower as a shop at sea level. There is just less oxygen for the engine to burn at the higher altitude. What are less obvious are the other weather condition effects on the engine. So in order to compensate for this all advertised horsepower is “corrected” to several different industry standards.

SAE:
"SAE (Society of Automotive Engineers), USA. Power is corrected to reference conditions of 29.23 InHg (99 kPa) of dry air and 77 F (25°C). This SAE standard requires a correction for friction torque.

STD:
STD is Another power correction standard determined by the SAE. Power is corrected to reference conditions of 29.92 InHg (103.3 kPa) of dry air and 60 F (15.5°C). Because the reference conditions include higher pressure and cooler air than the SAE standard, these corrected power numbers will always be about 4 % higher than the SAE power numbers. Friction torque is handled in the same way as in the SAE standard."



Here is some quick math (using assumptions and round numbers):

STD:
Air Temperature: 60F
Absolute Pressure: 29.92 inches Hg
Relative Humidity: 0%

Relative Horsepower : 104.8%
Air Density: 1.223kg/m3
Relative Air Density: 99.8%
Density Altitude: 67feet
Virtual Temperature: 60F
Vapor Pressure: 0 inches Hg
Dyno Correction Factor: .955

SAE:
Air Temperature: 77F
Absolute Pressure: 29.23 inches Hg
Relative Humidity: 0%

Relative Horsepower : 100%
Air Density: 1.157kg/m3
Relative Air Density: 94.4%
Density Altitude: 1952feet
Virtual Temperature: 77F
Vapor Pressure: 0 inches Hg
Dyno Correction Factor: 1

the dd's don't have either of those. I believe the only actual inputs from the operator are transmission type, centre diff type and tyre pressure, so the operator cannot apply varying correction factors which is exactly why they are so repeatable between different operators and even different dynos.

André

[HilbillyHomeboy]

Re: weather station.

Guess what putting a space heater under the station does? Yes, I absolutely know people that have done that...

Jeremy

[IPD]

re: Weather station.

Guess what putting a space heater under the station does? Yes, i absolutely know people that have done that...

Jeremy

brilliant!

[BaadVR4]

Deliberate deception is always possible. I'd hope to not ever select someone who would do that. But on another topic as yet unmentioned, the Mustang Dyno employs an eddy current brake as well as an inertial drum brake (as used by DynoJet). Mustang Dynos claim this more accurately reflects aerodynamic and rolling friction losses. Not sure how accurate that claim is, but I am pretty sure it will affect the final numbers.

Re: weather station.

Guess what putting a space heater under the station does? Yes, I absolutely know people that have done that...

Jeremy

[HilbillyHomeboy]

Yeah, since it was brought up, I was just throwing it out there that the weather station is far from infallible. That's one reason why I started running my numbers uncorrected.

Jeremy

[Permanent grin]

The problem is the world of dynoing is bigger than just Dynojet or Mustang!

The ONLY correction factors used by the dd are the ones that correct for atmospheric conditions and AIT. The software does corrections automatically based on readings from its integrated weather station and AIT probe.

Atmospheric Correction Screen
Inlet air temperature
Ambient temperature
Barometric pressure
Relative humidity
Mechanical efficiency (Dyno Dynamics ATMC2 only)
Resultant correction factor

Taken from here

To explain in detail I copied this from a post on EvolutionOz.net

The whole point of a dyno correction factor is to be able to test in different atmospheric conditions (eg. summer, winter, different locations) and to still be able to compare the results from any given test.
As the engine relies on mass air flow to make power any change in air density can have a large effect on the output of the engine. If the air is more dense (lower temperature, lower atmospheric pressure) you will make more power, if the air is less dense (higher temperature, higher atmospheric pressure) you will make less power.

So what happens is a "standard air condition" was created. A formula was then derived taking into account the air density components (temperature, pressure and humidity) that allows a correction factor to be calculated.
This correction factor is applied to the measured power to give a result AS IF THE ENGINE WAS ACTUALLY OPERATING on a day with " standard air conditions".

As it happens there are a few different correction standards!
The Dyno Dynamics dyno uses SAE J1349 however with the Mainline dyno you can select from a number of corrections including SAE J1349 however most people use J607.
The main difference between J1349 and J607 is the "standard" operating conditions chosen.

SAE J1349 "standard conditions"
Barometric pressure = 990 mb
Humidity = 0%
Temperature = 25 degrees C

SAE J607 "standard conditions"
Barometric pressure = 1015 mb
Humidity = 0%
Temperature = 15 degrees C

For example another non automotive standard
International Civil Aviation Organization (ICAO) "standard conditions"
Barometric pressure = 1013.5 mb
Humidity = 0%
Temperature = 15 degrees C


To highlight the difference at 20C the J1349 correction would subtract power and the J607 correction would adding power!

The difference in the "standard day" conditions chosen means for any given conditions J607 will always read higher than J1349.

So some points.
1) To compare dyno data both dynos have to be using the same correction factor!
2) To compare Dyno Dynamics data with Mainline data the Mainline dyno needs to select J1349 for the print out. This can be done with the Mainline dyno as the raw data is saved so you can select either correction standards when printing out results, or even print out both.
3) The position of the intake air temperature (IT) sensor on the Dyno Dynamics is very important as it can dramatically effect the correction factor.
4) With the Dyno Dynamics dyno the barometer pressure must be entered by the operator as read from the dyno shops own barometer, this also can dramatically effect the correction factor
5) The local barometer pressure typically published for weather purposes is a altitude corrected pressure (corrected-to-sea-level atmospheric pressure ) not the actual atmospheric pressure.


Example correction.
Dyno test conditions
Barometric pressure = 932 mb
Humidity = 68%
Temperature = 19 degrees C

J607 correction = 1.114
J1349 correction = 1.081

Base "uncorrected measured power" 236kW
J607 corrected power = 262.9 kW (Mainline J607 selected)
J1349 corrected power = 255.1 kW (Dyno Dynamics)

Note: Section 5.1 of SAE J1349 AUG2004 standard makes it clear that the equations are not intended to provide accurate corrections over an extremely wide range, but rather that the intended range of air temperatures is 15 to 35 deg C (59 to 95 deg F), and the intended range of dry air pressures is 900 to 1050 mb (26.58 to 31.01 inches-Hg). Values outside of this range may produce inaccurate results for SAE Relative Horsepower and Dyno Correction Factor, but all other calculator results (such as Density Altitude, Air Density, etc) will still be correct.

It would appear there are only 2 areas a dd operator CAN affect the results 1) inputting a false barometric pressure if the dd is one that doesn't have the integrated weather station or 2) incorrect placement of the AIT probe such as deliberately putting it in a hot part of the engine bay.

It would further appear that some other types of dyno rely heavily on the operator using the correct SAE correction J607 or J1349.

I reiterate my earlier point that there is less a dd operator can do to mess with the figures, therefore they are more repeatable in terms of results between different dyno's and operators.

If Joe Blogs is off sick and he dyno'd my car last time, I want to know that Fred Blogs will get the same results that Joe would have.

André

[Ray Pampena]

DD has an "x" correction key. you can take the dyno numbers and have them multiplied by ANY % that you feel like entering. so dyno a car that makes 300whp and enter 40% in there and you get a nice dyno graph of 420whp. ask anyone who USES a dyno dynamics about that. the same goes for the mustangs dyno and the superflow. thats why you see them running so called dynojet numbers.

they dynojet has NO USER CORRECTION.. only weather which all dynos have. the weather reads live weather and gets printed on the bottom of the chart to weed out any heat lamp people. if you see a dynojet run thats really high power... and it has the weather printed on the bottom... its real and thats that. theres no other math involved.

im not saying dynojet is the best. ive tuned on many different dynos and they all have cool features. dynojet is the only one that is not user definable with an "x" multiplier and is the most widely used whp standard in the US. i dynoed my red car a year ago and made 520whp. i dynoed it the other day and it made 523whp then went 10.97@126@3825lbs on regular tires so i think the numbers are accurate too

[GTOJOE]

What is this "shoot-out mode" then... isn't it a mode that cannot be modified so there is no possibility of fudging the numbers by the operator?

[Permanent grin]

Ray, I would go with that and agree with your figures translating to track times on street tyres. Mine was making very similar power (measured on a dd) and ran 10.96 @ 124 with a high terminal of 128.

The x factor as you say is also quoted on the graph for all to see as are thee baro readings, therefore is as transparent as Dynojet which may be the most popular in the States but is it worldwide?

André

[Hans@GZP]

But Ray, you can change your elevation!!!!