Question on SAE vs STD. From what I understand that they are conversion factors

On my dyno graph, it says .98 SAE, on a friends (different dyno and region) I saw 1.02 SAE....

What does this mean?

My common sense leads me to believe....

SAE < 1.00 = SAE # will be less than the STD #

1.00 SAE #'s will = STD #'s?

SAE> 1.00 = SAE # will be greater than the STD#

If Im completely off base, can someone briefly explain to me.

 

14 views...no response. Hopefully someone can chime in. Not of the essence....but something Ive been wondering for a while

 

SAE and STD just refer to different reference conditions (temp, baro, humidity) used to correct measured power numbers. SAE corrects to a lower temperature than STD. So all else being equal, SAE will yield about 4% lower numbers than STD, but SAE is the standard of the OEMs.

When you see the correction factor of 1.02, that means that the conditions you were tested in were 2% away from the standard, so your raw numbers are adjusted by that factor to give you a number that is more consistent for the purposes of comparison. This allows us to reduce the influence of testing in January versus July, but keep in mind that it's not a perfect correction since it only accounts for airflow and not other aspects of combustion.

 

thanks

 

For combustion to occur, oxygen is needed. The amount of oxygen in a given about of air is affected by air temp, absolute pressure, and vapor pressure. SAE (Society of Automotive Engineers) came up with SAE J1349 to equalize the results of various dynos for differences in the air. Everyone should be stating dyno results in SAE.

I found this at: SHELQUIST ENGINEERING-DYNO CORRECTION FACTORS

**************************************** **************************************** *************************
Originally, all of the major US auto manufacturers were in or around Detroit Michigan, and the dyno reading taken in Detroit were considered to be the standard. However, as the auto industry spread both across the country and around the globe, the auto manufacturers needed a way to correlate the horsepower/torque data taken at those "non-standard" locations with the data taken at the "standard" location. Therefore, the SAE created J1349 in order to convert (or "correct") the dyno data taken in, for example, California or in Tokyo to be as if the data had been taken at standard conditions in Detroit.

For example, at 85 deg F, 24.71 in-Hg absolute pressure and 0.121 in-Hg vapor pressure, the engine only produces about 81.1% of the SAE rated power so that the required dyno correction factor is 1.233. Therefore, when dyno testing under these conditions, it is necessary to multiply the measured torque and horsepower values by the correction factor of 1.233 to determine the SAE corrected readings. The dyno correction factor takes into account all of the effects of temperature, altitude, atmospheric pressure and humidity to arrive at corrected horsepower and torque values.

The air temperature should ideally be the temperature of the air that is going into your engine.

The absolute pressure is the actual atmospheric pressure, also called station pressure. This is not the barometric pressure or altimeter setting as is typically reported on the local weather report.

The vapor pressure is the partial pressure of the water vapor in the air.

For these calculations, the standard reference conditions are: Air temp 77 deg F (25 deg C), 29.235 Inches- Hg (990 mb) altitude-corrected barometric pressure, 0 ft ( 0 m) altitude, 0% relative humidity.