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First off it would be very hard to be in 0% humidity. Quite possibly you dont understand the term that the forcasters use when they say humidity. When you hear it on the news they are speaking of relative humidity. Now relative humidity is just that "relative" to the tempreture outside. Now we must understand the thermodynamics of air. The atmosphere can only hold so much water, we give that value a 100% however, it differs with the tempreture. So when the tempreture is 80* outside the relative humidity is low however the water concentration is not all that low. If you are comparing 50* to 80* and one is 40% humidity and the other is 60% humidity they are not all that much different because 80* holds less water so it is closer to its maximum capacity. So if you were to keep the water concentration constant and slowly cool the air you would see an increase in relative humidity. When you get to 100% you get to a point called the "dew point" Commonly seen as fog. Air can only hold 4.9gm/m3 of h20 when the air is cooled beyond this point (freezing) you get ice. Now lets get to your question about performance...
Lets take a given volume of air, say 1L in two seperate containers (1L per container). One having a ralative humidity of 80% @ 80* and one having a relative humidity of 0% at the same temp which one would contain more air?The one with no humidity because like everything in this world water has a mass. So obviously pure air with no h20 in it would have more room for air, the jar with h20 (in vapor form) now has a reduced volume of air to work with because that volume is taken up by the h20. We all know that air=power so the jar with more air will make more power. So in anwer to your question the lower the humidity the more air concentration in the atmosphere the faster you will run. (though you will run lean and this could be worse....but lets not get into that). When you see a nice film of dew on your roof at the track, the temp has reached the "dew point" and the air is COMPLETELY saturated with h20.The point between when air is at the dew point and between freezing you will form condensation.(like on your cold glass of coke) RELATIVE HUMIDITY- is NOT an accurate measure of humidity, it is RELATIVE to the temp. changing temps doesnt necessarily mean chaning concentrations in h20 in the air. A more accurate way to see if it would effect performance is to get the actual huidity content.(we can get into things like barometric pressure and such) Now go explain to your friends and amaze them with your intellegence
With the exception of his spelling of "intelligence", Mike TexaSS hit the nail on the head.
In short, water vapor displaces oxygen in the air (vice mixing with it). As such, humid air is less dense (and has less power making potential), and dry air is more dense (and has more power making potential).
A better indicator of how much moisture is in the air is to look at the Dew Point Temperature. Lower is good, higher is bad.
another way of looking at it is this, the water should evaporate in the intake and cool the charge allowing for cooler air. those arent my words but i have heard that on more than one occasion. it does make sence to me but i dont know how much the extra cooling offsets the displacement of oxygen. i think that may be the reason humidity doesnt effect you'r E.T. as much as other things because it partially negates itself
not sure if has been said beacouse i dontwanna rerad all the above posts but to some degree the air is more dense therfore more drag will result also more moisture wil result in more wheelspin and finally damp air has more water thus less oxygen then dryer air thus less combustusion will result
humid air is less dense than dryer air. This means that in a certain amount of mass, there is more air if you will in the dryer air over the humid..... it makes sense in my head, I hope it makes sense here
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This is why you can hit a baseball much further when you have a 100 degree temp and a 75 dewpoint versus a 100 degree temp and a 30 dewpoint. It is easier for the ball to travel through the humid air because it is much less dense, even though it feels very muggy outside.