water grans

Kesler at the track is the best.

 

ok - this is probably a stupid question, but what is the difference between humidity and the # of water grains, or are they the same thing?

 

humidity vs. water grains

Humidity is volume based. Water grains are mass (weight) based. Both should work for tuning. Water grains are calculated from humidity measurements.

More on this and their effect on horsepower in the Motorsports Standard Atmosphere book that we carry.

Bob Szabo
www.racecarbook.com
(916) 419 6649

 

Water grains is a measurement of ABSOLUTE humidity, which I think is more accurate description of water vapor in the air than relative humidity.

For example relative humidity reflects the relative amount of water that air can hold at a given temperature. Change the temperature and the humidity will change even if net amount of moisture in the air remains the same. In fact a 1ºF change in temperature can change the relative humidity by 2%. If outside air at 85ºF and 60% RH is cooled to 72 degrees without any moisture removal, the RH will increase to almost 90%

1 pound of water= 7,000 grains

absolute humidity (specific humidity)--amount of water vapor in the air (absolute uses weight per volume of air)

capacity of air to hold moisture depends on temperature so its capacity varies

WATER VAPOR
CAPACITY TABLE
per one cubic foot of air

temperature grains
30 1.9
40 2.9
50 4.1
60 5.7
70 8.0
80 10.9
90 14.7
100 19.7


Relative Humidity--ratio of amount--percent

RH = (amount of water vapor the air has/what could have) x 100 = RH

OR

RH = (has/could have) x 100

example: temperature 70°F; has 2 grains of water vapor

reading from the table, the capacity is 8
so

(2/8) x 100 = .25 x 100 = 25% RH

This was copied from a website. I don't know. It is not from me.
I will tell you 100% that water grains over 100 affects et way more than humidity raising and lowering. High humidity with lower grains is no big deal. Lower humidity with high grains is. Can both happen: Hell, I am not interested in reviewing the logbook right now.
Wags

 

The second paragraph makes sense.
Never had that question pop up before.
Wags

 

Hmmm... no one finds this interesting? Or wants to argue the point?
Wags

 

Grains of water is just a count of the number of grains in a pound of air. Temp. doesn't matter. Relative humidity is how much water is in the air vs. what is the maximum it could hold at that temperature.

 

I was just thinking water grains is a real number. The air coming into my engine is a real number. RH is a calculated number. This is why when we had 85% humidity the boat could run x number or x number + or -. Because RH is calculated. Higher temp, same amount of water grains= less RH. The grains per cu ft was the same, therby displacing x amount of "air".
It did not change .1 et at 101 gr and quicker under that... we just found (for our application) RH was pissing in the wind way more than water grains. (now it makes sense why)
Now, with that being said... It is entirely I possible/ probable I am missing something and it just seems to work out this way. Beats me. I just found the explanation and found it interesting, so I posted it.
Wags

 

Either I misread the explanation by guy x, or you did. I thought temp effected how much water (measured in grains) air COULD hold. And RH was a percent based upon how much water the air could hold vs what it was holding. Not the other way around...
Put another way... water grains is a real number measured. If we took 1 cu ft of air and wrung it out it would drop out x grains of water. So, water grains is torque... RH is horsepower (a calculated number).
Anyway.. its late I may be wrong.
Wags