A dyno run on my car w/dyno set to CF: STD came up with 426 hp and 392 ft-lbs.

Same run but set to CF: SAE produced 414 hp and 384 ft-lbs.

Would someone please give me a technical explanation of why the SAE numbers are lower? I imagine it's some sort of correction factor calculation? If so, correction for what?

TIA

Rick

 

I was told that the SAE has a air/Temp environmental correction factor, where the standard factor is what all the aftermarket and magazines use. Because it usually has the bigger numbers. They are real numbers but have diffrent correction factors. This is what I was told.

 

SAE (Society of Automotive Engineers) numbers are corrected for Barometric pressure, relative humidity, and air temp... there may be one more factor I have forgotten, but you can Google it if it really matters. The atmospheric conditions (and subsequently engine output) are "corrected" to a standard value set by SAE using those environmental parameters in an attempt to factor out atmospheric conditions when comparing engine output.

For example: you go to the dyno in the winter time when the air is dry and cool on a nice day (high barometric pressure). You get a dyno graph with STD numbers and Corrected numbers. Then 6 mos later you go back to the SAME dyno (assuming it is calibrated and well maintained and you haven't changed anything), the weather is very different - raining (high humidity, low barometric pressure, moderate temps). The Corrected numbers "should" be the same while your STD numbers will be a little lower. There is a margin of error in the formula, which is why I say "should".

I believe the formula attempts to correct atmospheric conditions to reflect 1 atmosphere at 70*F with 50% relative humidity. I'm not positive on those numbers, but they're in the ball park. So, the reason your Corrected numbers were lower is because one or more of the atmospheric variables was better than the SAE standard value ( it was cooler, or higher baro pressure, or lower humidity, etc). So, to "correct" your engine output, the formula spit out a value less than 1. If it were the other way around and the temperature was hotter than the standard and it was more humid, the STD number would be lower, and you would see a correction value greater than 1.

 

STD is what your car made that day, in those conditions, no correction factor.
SAE is just the correction factor used to give different users in different areas standardized results that can be used for comparison.

 

No. STD IS a correction factor as well. It's not as strict as SAE though since it reads about 3% higher or so.

 

Correct, I was thinking of the uncorrected numbers.

 

The STD correction uses a lower temperature, which will often increase the HP numbers a bit if you are above the temperature. I think it is something like 60 degrees F.