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and, of course, will not support combustion.
Water Vapor
Water vapor (grains, Gr) is the same information as ‘Vapor Pressure’ expressed in
different units. Some race teams use 100 Gr as the threshold for making water vapor
related tuning changes. Engine fuel flow and ignition timing may need to be increased
above the threshold.
Wet Bulb Temperature
Wet bulb temperature refers to using an expanding liquid type thermometer with a water
soaked cotton wick over the sensing bulb. This technique produces a lower temperature
indication for lower humidity conditions due to evaporation. The wet bulb temperature and
the dry bulb temperature can be used to calculate ‘Relative Humidity’.
Good Air / Bad Air.
The atmospheric conditions that make air quality better for racing are: lower temperature, lower
humidity, and higher air pressure. Conditions that make the air worse for racing purposes are:
higher temperature, higher humidity, and lower air pressure. Lower Correction Factor numbers,
lower Density Altitude numbers and higher Air Density Ratio numbers all mean better air quality.
The variables that cause the Correction Factor and the Density Altitude to decrease (smaller
numerically), as well as the Air Density Ratio to increase (larger numerically), are: a lower
temperature, a lower relative humidity, a higher barometric pressure (as measured with a
barometer), or a lower pressure altitude (as measured with an altimeter). Typically, the STD
Correction Factor will be between .98 (better) and 1.15 (worse); the Density Altitude will be
between -300 ft. (better) and 8,000 ft. (worse); the Air Density Ratio will be between 85% (worse)
and 103% (better).
Atmospheric changes can be experienced when going from track to track or from Spring to
Summer to Fall at the same track. The typical change in air quality from the heat of the day to the
cool of the night is usually not very large. However, the RaceAir Pro will compensate for changes
in all of the weather variables, no matter how small.
Remember, as the Correction Factor and the Density Altitude increase (larger numerically),
performance will decrease. As the Correction Factor and Density Altitude decrease (smaller
numerically), performance will increase. The lower the Air Density Ratio (smaller numerically),
the leaner the jetting needs to be and the higher the Air Density Ratio (larger numerically), the
richer the jetting needs to be.
Sampling Information.
The top portion of the RaceAir Pro, where the red stripe is, contains the weather sensors. During
the sampling process, air is drawn in through the diagonal slits in the faceplate by the internal fan.
The air is then exhausted through the vents on the upper left side of the case. These air passages
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