Dyno Sheets - SAE vs. STD Correction
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Instructor
Joined: May 2007
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From: Wexford, PA
Dyno Sheets - SAE vs. STD Correction
I was looking through some dyno sheets and noticed that some shops use SAE correction values on the Dynojet while other use the the STD correction values. 
I did a little research and found a good read:
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
I did a little research and found a good read: 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
Le Mans Master
Joined: Jul 2005
Posts: 5,328
Likes: 405
I was looking through some dyno sheets and noticed that some shops use SAE correction values on the Dynojet while other use the the STD correction values. I did a little research and found a good read:
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."
I did a little research and found a good read: 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."
http://www.land-and-sea.com/dyno-tec...horsepower.htm
It also has the formula for the SAE HP correction that you used to get the 4.5% difference between SAE and STD.
Also, I think you meant to say friction HP (not friction torque) when discussing SAE and STD power corrections. SAE and STD torque readings have friction torque corrections applied.
Overall a good write up. It should be noted as stated at the end of the above link that SAE HP readings with correction factors of more than 7% can not be stated as accurate because the formula is only good for a limited range of absolute pressure and temperature conditions. This is stated in the procedures for testing in SAE J1349. The changes in air quality can not be modeled over a wide range with a simple formula. Of course for our purposes, it doesn't really matter...not like we're going to the moon or something. Again, good job.
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