SAE vs STD vs Actual HP Readings

[HIGH ROLLER]

Doing alittle research just thought i would pass this on to you:

SAE uses a barometer reading of 29.23 and a temperature of 77 degrees for part of its correction factor.

STD uses a barometer reading of 29.92 and a temperature of 60 degrees for part of its correction factor and is usually 3-4 percent higher than SAE numbers.

Actual HP means that the actual horsepower was achieved with no correction factor applied.

 

[APTEN]

I thought % difference between SAE and STD will depend on the temp and BP of the day.

Brian

 

[Black2003Cobra]

I've been over this myself, many times. According to SAE J1349, the correction factor is given by,

CF = 1.18[(29.235/Pd)*((Tf + 460)/537))^0.5] - 0.18

where Pd is the dry-air partial pressure at sea level and Tf is the temp in deg F. Therefore, since the SAE conditions are Tf = 77 F and Pd = 29.235 in Hg, and STD conditions mentioned here are Tf = 60 F and Pd = 29.92 in Hg, the conversion between STD and SAE is always 4.7% (STD = 1.047*SAE). It doesn't matter what the ambient conditions are. When correcting the raw numbers, that's where the ambient conditions come in. The reason people post different numbers between SAE and STD is because the conditions for STD, don't seem to be, uhm, standard. If you search around, you'll find some use Tf = 59 F, and others use Tf = 68 F, for STD. If you look long and hard enough, you'd probably find more definitions.

 

[HIGH ROLLER]

Very good info about the Tf numbers being different on dynojets that explains why some dynojets read a higher STD number than others do. I dyno at several different dynojets and at 1 dynojet i am always about 10HP difference between SAE and STD and at the other dynojet i am always 15HP difference between them and the weather can be 90 degrees outside or 30 degrees outside and it is always the same outcome at both places.

 

[Black2003Cobra]

Yeah, I found these variances really frustrating. It would be nice if the standards really were standard, wouldn't it!

 

[Joe Lynch]

Use SAE.

 

[CobraBob]

Since most folks use the SAE correction that is what I've always used.