if your talking about engines which would you rely on more? the 20.9% you talking about is relative to the amount of space taken up at altitude by the same amount of space at sea level. useable oxygen for a motor is the same as useable oxygen for an animal. because just like an engine. out lungs are only capable of flowing the same amount of volume at either altitude. for scuentific study of other atmospheric things sure 20.9 will work great . but for formulating motor effeciency at altitude. its not.
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20.9% is what it is and doesn't ever change. It is a constant that needs no adjusting, it is alway 20.9% no matter what. You are the one that inserted that number into this conversation, not me. Then you posted some BS that the oxygen percentage drops with altitude, not me. Then you told me to "try again". Try as I might, you don't seem to understand common physics and simple math.
The biggest culprit that altitude poses it pressure, not oxygen PERCENTAGE of the incoming air. If you are talking about the actual amount of air (including the 20.9% oxygen) that the engine can intake then that is a totally different story and that is measured in cubic X (liters, feet, etc), not oxygen percentage. This is where the pressure comes into play. An engine (and human for that matter) can draw in more dense air if the pressure is higher and in turn can get more oxygen molecules but that air still only contains 20.9% oxygen.
That brings us full circle. We all live in a pressure. Sea Level is 14.7, 5000 feet is 12.5. When you go full throttle, that pressure is all on the intake ports and pushes the air into the engine. The engine doesn't suck the air in like many believe, the atmosphere pushes it in.
When it comes to pressure on a gauge, zero isn't really zero. A gauge that reads zero at seal level is off by 14.7 psi and a boost gauge that reads 15 psi at seal level is also off by 14.7 psi. 15 psi boost at sea level is really 29.7 psi but that would confuse everyone so we always start at 0.
Think of the atmospheric pressure at sea level as a 14.7 psi turbo pushing in 250 CFM at full throttle. At 5000 feet the 12.5 psi can only push in the equivalent of 213 CFM. Less air, less oxygen, less power. Now add 15 psi of boost from a turbo, the pressure at the intake at sea level is now 29.7 and (theoretically) you can now push the equivalent of 505 CFM but at 5000 feet the 15 psi boosted pressure is only 27.5 psi which will (theoretically) allow the equivalent of 468 CFM. Again, less CFM, less oxygen and less power. To (theoretically) get the same CFM, oxygen and power at 5000 feet, you would need to adjust your boost up to 17.2 psi. Of course, these numbers are all just examples under perfect conditions and the real numbers will be very different but the effect will be similar.
Again, unless there is a way to fiddle with the boost, a Turbo Talon will make less HP at 5000 feet. My educated/experienced guess is it will be around 10-12% less power. A dyno will confirm if I am right or wrong.
this is why airplanes have oxygen incase of release of cabin pressure. hypoxia at high altitudes
) can learn a lot!!
