The myth about humidity and its effects on horsepower.

[RadialFin]

those numbers are percentages, reread.

Ya know Al, I really try to give you credit and be patient with your stubbornness beyond the point most people ignore you. But sometimes you're too quick to try and make a point often leaving your without one and discrediting practically all of your work. Take your own advice. I specifically acknowledged they were percentages, I even included a % sign.
Here I'll respost it for you so you can read it again yourself.

"I tell you what though, let's say for simplicity sake the % in the screenshots is HP. I'd rather be making 101.6HP over 100.7 anyday"

Additionally, for the purposes of this exercise there is no mathematical reason, that this correlation of percentage to HP cannot be applied if it's kept to hundreds. HP simply makes it more palatable for some people.

 

[JPM]

Eliminate prepping of tires and it will become obvious...lol

 

[Bob Evans]

Eliminate prepping of tires and it will become obvious...lol

Whether the idea is right or wrong, WKA tried eliminating prepping and all they ended up eliminating was their dirt series.

Radialfin-- you know, regardless of how Al brought the topic up, it's resulting in a discussion of a type that we just don't see very often anymore.

 

[alvin l nunley]

"I tell you what though, let's say for simplicity sake the % in the screenshots is HP. I'd rather be making 101.6HP over 100.7 "

It seems I was a little hasty and didn't see that "%" sign. You've never done the same?

Let's see; 101.6 HP versus 100.7 HP = .9 more horsepower. That's only a .09% increase in horsepower. 9/100's I doubt you would ever feel this on the track. I wonder if you could even measure it on a dyno with any consistency.

Now let's look at it this way; 101.6% versus 100.7% of a 10 HP engine = .9%. 9/10's

I don't see the simplicity in your manipulation of my numbers!

"more palatable for some people...." maybe so, but I don't like talking down to people.

And the fact that I missed that %, in your response, hardly invalidates everything I've ever said. It leaves me questioning your motives. I never claimed to be perfect! If you had just pointed out my oversight, rather than going off the edge, I wouldn't have said anything.

 

[Jamie Webb]

not questioning your numbers, but to reach 95% humidity, it's got to get real hot, and when it gets hot, in almost all cases, the air density goes down. HP is much more dependent on air density than it is on humidity.

I can do the same calculations, not changing the temperature or barometric pressure, just the humidity, and get a much smaller percentage change.

Here's today's forcast/actual numbers in Florida:
8:00 am 74 °F 97% 30.06in
10:00 am 84 °F 73% 30.05in
12:00 pm 89 °F 62% 30.04in
2:00 pm 89 °F 58% 30.04in
4:00 pm 89 °F 54% 30.01in
6:00 pm 86 °F 59% 29.99in
8:00 pm 81 °F 70% 30.00in
10:00 pm 76 °F 86% 30.03in

Doesn't always have to be hotter for humidity to go up.

 

[alvin l nunley]

Here's today's forcast/actual numbers in Florida:
Doesn't always have to be hotter for humidity to go up.

what most people don't know is, and I don't want to make you feel dumb, those numbers are the relative humidity and what that means is, how much water vapor the air is holding as a percentage of what it could hold at that temperature. The curve showing how much water vapor, (a gas like any other gas) the air can hold is a parabolic curve. This means that the hotter it gets the more water vapor the air can hold. The curve gets steeper and steeper as the temperature rises. Using that curve, where the air is holding as much water vapor as possible, at the current temperature, the humidity would always be 100%.

It's possible to have 85% relative humidity at 65 degrees. This doesn't mean there's a lot of water vapor in the air, it just means the air is holding close to its maximum amount at that temperature.
At 100 degrees, with the humidity of 100 percent, the air is holding 4% water vapor. Now 4% could slow you down, but not nearly as much as 100 degrees. Air density, depending on the barometric pressure, would be way down.

I have a weather service icon on my desktop, and they actually report the barometric pressure corrected to sea level. When I went to check the weather in Colorado, I was very surprised at how high the barometric pressure was, until I realized they were using corrected for altitude pressure readings. This is good information if you are flying an airplane.

 

[RadialFin]

Al, I feel like you do it a lot hence it struck a nerve.

 

[Bob Evans]

Al-- If relative humidity is entered into the calculator, isn't entering the temperature redundant?

 

[MikeFlipp]

Al-- If relative humidity is entered into the calculator, isn't entering the temperature redundant?

Al, relative humidity doesn't have a direct correlation to temperature, except in calculating 100%, or the dew point, correct?
Isn't dew point the maximum relative humidity for any one given temperature?
At any one given temperature, the humidity level can be anywhere from 0% relative humidity to the maximum relative humidity, which is the dew point or am I missing something?

 

[MikeFlipp]

http://www.ianrpubs.unl.edu/epublic/live/g1849/build/graphics/g1849-1.jpg

Like this chart shows...????

So you would have to enter BOTH relative humidity % and temp because they can be directly associated, but not necessarily, correct?

 

[alvin l nunley]

Al-- If relative humidity is entered into the calculator, isn't entering the temperature redundant?

Hardly, you can have 80% relative humidity at any temperature. 80% relative humidity at 60 degrees means there's a lot less water vapor in the air compared to 80% relative humidity at 90 degrees. The air density gauge measures barometric pressure as affected by the ambient temperature. Hot air is thinner than cold air, unless the barometric pressure goes up. I've seen a reading of 103 percent with a temperature of 80 degrees in San Diego. Very close to the ocean you know.

 

[alvin l nunley]

Al, relative humidity doesn't have a direct correlation to temperature, except in calculating 100%, or the dew point, correct?

Relative humidity (RH) is a percentage of how much water vapor there is in the air compared to the maximum water vapor the air could hold at that temperature. As I have said before, the air can hold more water vapor the hotter it gets. It's a parabolic curve.

On a cool morning in my dyno room one day, the RH was 80%, at 65 degrees. As it warmed up, as it was in the summer, the temperature went up to 80 degrees, and the RH went down to 50%. Just as a guess, the temperature went up, but the water vapor in the air stayed the same, thus a lower relative humidity.

This relative humidity thing seems to be a little more confusing than I thought.

The reason you feel so wet and sticky, when it gets hot and humid, is because your perspiration doesn't evaporate. At the Adams kart track in Riverside California, which is close to the desert, it can get up to 100° and you don't feel wet and sticky at all because your perspiration evaporates in the dry air. I've seen a relative humidity reading there of 5% on a hot summer day.

 

[alvin l nunley]

http://www.ianrpubs.unl.edu/epublic/live/g1849/build/graphics/g1849-1.jpg

Like this chart shows...????

I think that chart unnecessarily complicates things. If you are trained to read it, very good, and I'm not saying it's not a good chart, it just not something you could use at the track. An air density gauge is so simple. When it's up, bigger jet, when it's down, smaller jet.

Most of all, I wish people would stop telling me that these 4 stroke single cylinder engines don't respond to differences in air density.

 

[alvin l nunley]

Al, relative humidity doesn't have a direct correlation to temperature, except in calculating 100%, or the dew point, correct?
Isn't dew point the maximum relative humidity for any one given temperature?
At any one given temperature, the humidity level can be anywhere from 0% relative humidity to the maximum relative humidity, which is the dew point or am I missing something?

As I understand the dew point, as the temperature goes down at night it reaches a point where the air can no longer hold the water vapor it contains. The water vapor returns to its liquid form and falls out of the air. If it gets cold enough, it freezes and we all know what that means.

So the next time you get up in the morning have to scrape that windshield, you now know where that ice came from.

 

[astglenn]

Dew point and RH are often described as being sort of the same thing. They are actually very different. When relative humidity and dew point get within about 2.5 degrees of each other, you can expect fog. Dew point is the description of the volume of water per sample period within an air column. RH is the air columns level of water saturation.

 

[MikeFlipp]

Thanks guys. Gets you thinking...

 

[Ted Hamilton]

I guess I assumed that fog was the result of moisture precipitating out of the air due to saturation point being reached, either through cloud movement or temperature drop... Clouds are either growing or shrinking, not constant, as the temp fluctuates and evaporative rates due to warming at the surface of bodies of water fluctuates due to cloud cover, axis of rotation of earth, and current % of saturation in air already... Is that roughly accurate?

 

[alvin l nunley]

I guess I assumed that fog was the result of moisture precipitating out of the air due to saturation point being reached, either through cloud movement or temperature drop... Clouds are either growing or shrinking, not constant, as the temp fluctuates and evaporative rates due to warming at the surface of bodies of water fluctuates due to cloud cover, axis of rotation of earth, and current % of saturation in air already... Is that roughly accurate?

everything you ever wanted to know about clouds, but were afraid to ask.
https://en.wikipedia.org/wiki/Cloud

 

[astglenn]

Ted. Yes. That is accurate for most of the deal. Fog and clouds are the same species but not directly related. Clouds need two things. A raising air mass (Convection) and moisture. There are several types of Fog. Convection Fog works pretty much like a developing cloud and needs a raising air mass. Several do not. The valley fog we get here is quite happy to just lay there about windshield high and make everyone's driving life miserable until a rising air mass pushes it up and out of its saturation zone.

 

[motorhead]

So who is to say this chart is accurate. I spent many years on the drag strip where HP is always crucial. Air density gauges disappeared in the mid eighties. Everyone that mattered had a weather station and not an air density gauge. We all measured humidity. And humidity was a HP killer. It cools the cylinder charge. Some actually use water to put out fires Al! Motors with high compression {16 to 1or more} didn't suffer as much with barometric pressure. We had high altitude set ups, sea level track set ups, high temp and high humidity set ups. Air density gauges are crude compared to a complete weather stations. We all new what altitude each track was. Their were always a few that didn't have this knowledge and they would only run good at a few tracks. Low barometer and high temps require different tuning. I would much prefer a good barometer to an air density gauge.