I calculate the correction factor the same way that SuperFlow does with its dynos, so I will go through that here. The correction factor takes the raw torque and HP numbers and corrects them to standard barometric pressure at sea level (29.92 inches of mercury) and 60 degrees Fahrenheit.
First, I looked up the weather conditions for Buffalo, KY 42716 on the NOAA site. I assume that these are close to the same for the dyno that Brent used. NOAA reports the barometric pressure as 30.06, the dewpoint at 63 degrees, the relative humidity at 46%, and the temperature at 86 degrees Fahrenheit. Using Google Earth, I went to Buffalo KY and found the altitude as 760 feet; again I assume that the dyno location is the same as this.
(Note: Brent mentioned to me earlier that he was seeing 91 degrees for temperature; if that is accurate, then the numbers I got from the weather service could be different than what the weather actually was at the dyno. The reason that most dynos have a weather station built in is to record the weather data at the same time as the engine is run on the dyno, so that the correction can be accurately calculated).
First we need to find vapor pressure from this information. If you don't have the dewpoint, but do have the relative humidity and the air temperature (like most dynos), go to this site and move the sliders around to set air temp and relative humidity, and you will get the dewpoint:
http://www.dpcalc.org/Next, with the dewpoint you can get the vapor pressure, at the National Weather Service site here:
https://www.weather.gov/epz/wxcalc_vaporpressureA dewpoint of 63 degrees gives a vapor pressure of 0.58 inches of mercury.
Now we need to find the actual barometric pressure, because all barometric pressures reported by the NOAA and the National Weather Service are corrected to sea level. Barometric pressure is given in inches of mercury, and conveniently 1000 feet of altitude is almost exactly 1 inch of mercury in pressure. So, at an altitude of 760 feet above sea level, the pressure will be lower by 0.760 inches of mercury. This means that the actual barometric pressure at the dyno, assuming the weather data is accurate, is 30.06 - 0.760, or 29.30 inches of mercury.
Now we have everything we need to calculate the correction factor. The formula is:
(Square Root of ((459.7 + T)/519.7)) X (29.92/(BP - VP)
where T is the temperature in Fahrenheit, BP is the barometric pressure, and VP is the vapor pressure. Solving for the first term, (459.7 + 86)/519.7 is 1.050; the square root of that is 1.0247. The second term is 29.92/(28.3 - 0.58), which is 1.0794. Now multiplying the terms together, the correction factor is 1.106, or 10.6%. So, uncorrected peak HP for Brent's engine is 463 HP, and corrected peak HP is 512. Uncorrected peak torque is 443, and corrected peak torque is 490 lb-ft.
Pretty strong 390...
Edit: OOPS! A typo got me. I originally had put 28.3 in the second term equation above, not 29.3. Bad mistake. The second term, with 29.3 used instead of 28.3, is 1.0418. Now, multiplying the terms together you get a total correction factor of 1.0675, or 6.75%. This means that corrected peak HP is 494, and corrected peak torque is 473. Sorry guys...
