Humidity and air/fuel ratio

[Joseph W Santora]

If I live in a consistently dry ( low humidity) area, does the lack of water molecules mean more air molecules and as a result a leaner mixture that that of sea level?
Joe

 

[hotshot]

Yes, less humidity provides more air (leaner fixed metering carb mix), but sea level pressure & humidity are not related.

I’m not sure what you’re asking at the very end of your question. Sea level would be a much leaner carb condition (more air) versus 9000’ elevations in Colorado.

 

[homemade]

I believe the O2 percentage in the air is the differentiating factor between low and high elevation.


Sent from my iPhone using Tapatalk

 

[hotshot]

Wierd, but it’s actually the same percentage, 21%.

But the lower pressure at high altitudes means the “effective” or “available” O2 you take in on a breath, or an intake piston stroke takes in is less.

Roughly 3% loss in engine power per 1000 feet rise, so definitely turbocharger time at 10k feet!

https://hypoxico.com/pages/altitude-to-oxygen-chart

 

[Canyon Angler]

Less barometric pressure at higher altitude means fewer milligrams of oxygen per gallon of air, all other things being equal. Percentages will remain the same regardless of elevation, but 21% of nothin is nothin

 

[wmazz]

It all about air density. The std is along the coastline, but inland at sea level with
low humidity the air density will be less (the density altitude will be greater than
the physical altitude).

I like using airdensityonline and choose a race track nearby. You can use that data
to determine density altitude, or estimate horsepower lost with the sae correction
factor.

Bill M.

 

[Canyon Angler]

It all about air density. The std is along the coastline, but inland at sea level with
low humidity the air density will be less (the density altitude will be greater than
the physical altitude).

I thought higher-humidity air was (counter-intuitively) less dense than drier air ... which is what causes problems with aircraft getting enough lift on their wings when it's really hot and humid...

 

[wmazz]

That is true. My example reflects the conditions on the west coast and inland
deserts that can be near or below sea level, and probably not than the east coast.

My only other experience with high humidity and air planes is with giant scale
pylon racers with 80 to 300cc engines. The airplanes flew 10 to 20 mph slower
in the fog, and they flew fastest in hot dry air with a low barometric pressure (about
5500') despite the hp loss.

Bill M.