EB vs GT Summertime Powerloss

[tw557]

The one thing that always confused me about my stock other then an intercooler ecoboost, was it always ran noticably smoother and also more torque on hot days of about 95-100 IAT. I even tried to research it but really can't find any good reason why this was the case. My Gt now likes the cold mornings though.

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[gadgtfreek]

Actually first they were blinded by the tail light flash when locking the car and as they staggered around disoriented they grabbed the hot prop rod in the hopes of stabilizing themselves.

HAHAHAHAHAHAHHAHA

 

[Zooks527]

At any given temperature and pressure pair, dry air contains a higher partial pressure of oxygen than humid air, as with humid air the water vapor in the air exerts its own partial pressure, decreasing the absolute percentage and partial pressures of all other gases.

WRT more spark advance, increasing humidity at any temperature results in a lower percentage of oxygen in the air (richening the mix for any fixed fuel flow) as well as reducing the density of the charge (also richening the mix at any given fuel flow). As the ECU's response in both cases will be to lower fuel flow to maintain its desired mixture regardless of timing, I would think a lower power output would be the result.

There is absolutely a difference as increasing humidity increases the heat capacity of air at any specific temperature, meaning that a set volume of air is able to absorb more energy per degree of temperature rise.

That being said, the effect is pretty small (perhaps a couple of percent increase in heat capacity going from dry to saturated at normal outside temperatures) and it would be a trick to actually notice the difference.

None of this means anything to the amount of power an ICE can create, in relation to humid atmosphere versus dry atmosphere. Humidity means the atmosphere contains that much less oxygen.

Have you ever noticed you can't fucking breath on a hot and humid day? That's because there's no oxygen in the atmosphere, your lungs are sucking in atmosphere that's packed with humidity instead of the oxygen you need.

And the same thing applies to your engine.

Did you bother to read earlier posts, or did you just feel like going off?

That being said, you personally are not going to notice the difference in oxygen percentage, unless you have some significant lung issues. If you do the math:

• The percentage of oxygen at sea level on a 90 degree day at 40% humidity is 20.6%.
• The percentage of oxygen at sea level on a 90 degree day at 80% humidity is 20.2%. (This is a day with an 83 degree dewpoint. Finding anyplace with that net of the bayou in August would be quite a trick.)

Unless you're at the edge of your limit on oxygen uptake (running a marathon, up hill, wearing a full pack) or have severe lung issues, you won't notice the 2% difference in oxygen content of the air.

You're actually reacting to the fact that you are overheating due to the limit on how much you can sweat in a humid environment, and your body is using more oxygen in an attempt to control your body heat. There is no similar issue with your car.


EDIT, 5/26: In the original version of this post, I stupidly swapped the percentage numbers for the two humidity numbers when copying from my calc sheet, causing the confusion below. This has been corrected above.

 

[NoVaGT]

Did you bother to read earlier posts, or did you just feel like going off?

That being said, you personally are not going to notice the difference in oxygen percentage, unless you have some significant lung issues. If you do the math:

• The percentage of oxygen at sea level on a 90 degree day at 40% humidity is 20.2%.
• The percentage of oxygen at sea level on a 90 degree day at 80% humidity is 20.6%. (This is a day with an 83 degree dewpoint. Finding anyplace with that net of the bayou in August would be quite a trick.)

Unless you're at the edge of your limit on oxygen uptake (running a marathon, up hill, wearing a full pack) or have severe lung issues, you won't notice the 2% difference in oxygen content of the air.

You're actually reacting to the fact that you are overheating due to the limit on how much you can sweat in a humid environment, and your body is using more oxygen in an attempt to control your body heat. There is no similar issue with your car.

Do us a favor, and post a link to where you got that information. I've be very interested in reading it through. I checked Google and got nothing.

Specifically about calculating oxygen percentage content in the atmosphere based on humidity and temperature.

 

[Paris MkVI]

All i know is hot and humid is bad for me. . .

I am not turbocharged.

 

[Zooks527]

Do us a favor, and post a link to where you got that information. I've be very interested in reading it through. I checked Google and got nothing.

Specifically about calculating oxygen percentage content in the atmosphere based on humidity and temperature.

I'm not sure I can find a link to my sophomore year Basic Principles of Chemical Engineering class from back in the fall of 1976.

However, I'd be happy to run the calcs for you.

Required inputs are:

• Temperature (picked 90F, because it's a nasty day if really humid)
• Humidity points (picked 40% RH and 80% RH out of a hat. 90F@80% is extreme for US)
• Atmospheric pressure (picked 1000 mbar to keep the math simple - 1013 mbar is a "standard" atmosphere, so we're nominally 350' above sea level).

Oxygen content of dry air = 20.95% (https://www.engineeringtoolbox.com/air-composition-d_212.html)

This gives us:
Vapor pressure of water at 90F = 47.45 mbar (https://www.omnicalculator.com/chemistry/vapour-pressure-of-water)

Partial pressure of water at 80% humidity = 47.45 mbar * 0.8 = 37.96 mbar
Partial pressure of water at 40% humidity = 47.45 mbar * 0.4 = 18.98 mbar

Partial pressure of all other gases at 80% humidity = 1000 mbar - 37.96 mbar = 962.04
Partial pressure of all other gases at 40% humidity = 1000 mbar - 18.98 mbar = 981.02

Partial pressure of oxygen @ 80% humidity = .2095 * 962.04 = 201.55 mbar
Partial pressure of oxygen @ 40% humidity = .2095 * 962.04 = 205.52 mbar

Percentage of oxygen @ 80% humidity = 201.55 mbar / 1000 mbar = 20.2%
Percentage of oxygen @ 40% humidity = 205.52 mbar / 1000 mbar = 20.6%



I hope you're all taking notes, there's going to be a short quiz next period.

 

[ice445]

I'm not sure I can find a link to my sophomore year Basic Principles of Chemical Engineering class from back in the fall of 1976.

However, I'd be happy to run the calcs for you.

Required inputs are:

• Temperature (picked 90F, because it's a nasty day if really humid)
• Humidity points (picked 40% RH and 80% RH out of a hat. 90F@80% is extreme for US)
• Atmospheric pressure (picked 1000 mbar to keep the math simple - 1013 mbar is a "standard" atmosphere, so we're nominally 350' above sea level).

Oxygen content of dry air = 20.95% (https://www.engineeringtoolbox.com/air-composition-d_212.html)

This gives us:
Vapor pressure of water at 90F = 47.45 mbar (https://www.omnicalculator.com/chemistry/vapour-pressure-of-water)

Partial pressure of water at 80% humidity = 47.45 mbar * 0.8 = 37.96 mbar
Partial pressure of water at 40% humidity = 47.45 mbar * 0.4 = 18.98 mbar

Partial pressure of all other gases at 80% humidity = 1000 mbar - 37.96 mbar = 962.04
Partial pressure of all other gases at 40% humidity = 1000 mbar - 18.98 mbar = 981.02

Partial pressure of oxygen @ 80% humidity = .2095 * 962.04 = 201.55 mbar
Partial pressure of oxygen @ 40% humidity = .2095 * 962.04 = 205.52 mbar

Percentage of oxygen @ 80% humidity = 201.55 mbar / 1000 mbar = 20.2%
Percentage of oxygen @ 40% humidity = 205.52 mbar / 1000 mbar = 20.6%



I hope you're all taking notes, there's going to be a short quiz next period.

You had your numbers backwards in your original post, I think that's where the confusion came from lol

 

[Zooks527]

You had your numbers backwards in your original post, I think that's where the confusion came from lol

Damn copy errors bite you in the ass every time !

Original post #33 fixed above. Thank you.

 

[Bull Run]

I live in the desert so DA goes up to 7500ft in the summer and the power loss is crazy, almost feels like I’m driving an Accord.

Same here. I drive around with a tuner attached so I can monitor ignition timing corrections and charge temps. Charge tamps usually go over 150 degrees during the summer here in stop-and-go traffic and trying a moderate to hard acceleration usually results in a good deal of negative ignition timing correction (I was on an aggressive 91 OCT tune).

E85's a different story as I rarely get any negative timing corrections and if I do, they are much smaller. I'll see how it does during the peak summer season.

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