Forced Induction and SwapsPost information/questions about Forced Induction methods (Turbos & Nitrous Oxide) and swaps here.
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Ok. Some common misunderstandings and myths resolved. Let's start with the basics.
The atmosphere we all breathe and drive our N/A beater cars in are breathing normal air, which is standard atmospheric pressure that is contingent upon your altitude above sea level. With that being said:
Relative pressure-Pressure deemed over and above the atmospheric pressure. Example, "I run 6 PSI of boost"
Absolute pressure- Pressure including atmospheric pressure. An example is, when we where in FL, we where about 20 ft about sea level, so we where almost exactly 1 Atmosphere, ( I will get into the measurements later), and running 6 PSI of boost would mean: Atmospheric + 6 PSI of turbo pressure
Now for the specifics on pressure:
1 Atmosphere ~ 14.5 PSI ~ 101kPA~ 1 BAR
^^These are all approx equal!
With this useful information, I can know explain absolute pressure of 14.5 PSI + 6 PSI of pressure, which would mean 20.5 PSI of ABSOLUTE PRESSURE
Now that we know the equivalents of one another, we can easily convert amongst each. IE: 1.7 BAR in relative pressure is approx 23 PSI ~ 160kPa.
:P
Now, that we understand that....Now the correlation of altitude comes into play. Recall as I stated before, that barometric pressure changes as altitude changes.....With that being said, at sea level or around there it is 101kpA. (Kilopascals, for those wondering ) Anyway, as the altitude increases the barometric pressure decreases because the air gets thinner. As a result, you will have a lesser base (atmospheric pressure) therefore will make less boost overall due to this fact. Understand?
At sea level, your pressure is 101kpa. So with 6 PSI of boost ~ 60 kpa that is ADDED to the 101 (speaking in terms of absolute pressure), is 160kpa. Great!
Now move to the 5000 ft above sea level (in the mountains or Denver), and it's approx 84kpa, which now means 6 PSI of boost ~ 60 kpa is ADDED to the 84, which means that it is 144kpa. This means you will see about 4 PSI on your boost gauge. This means LESS boost and LESS power on your boost gauge due to barometric pressure changes caused by altitude.
Questions?!??!
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__________________ Constantly redefining the 7thgen Civic's performance... Dezod Motorsports.
So you will need to crank the boost up as your altitude changes - albeit drastically like moving from Miami to Colorado Springs - in order to maintain the same power level right? How would this affect the AFRs?
__________________
Quote:
Originally Posted by LogicWavelength
This thread (T.E.A.R.S.) was inspired by speedfoos. We all know about his very public and very obscene battle against his car's engine.
There's a good chance that I'm not going to answer your PM.
So you will need to crank the boost up as your altitude changes - albeit drastically like moving from Miami to Colorado Springs - in order to maintain the same power level right? How would this affect the AFRs?
Yes, correct.
__________________ Constantly redefining the 7thgen Civic's performance... Dezod Motorsports.
along the same lines as Clint's question, since there is less oxygen in the air at higher altitudes, not to mention less air in general, couldn't arbitrarily cranking up the boost also cause greater issues since you'd be dumping in more fuel, but not necessarily taking in a great deal more oxygen? or do we assume the O2 content per volume of "air" moved remains constant?
) Anyway, as the altitude increases the barometric pressure decreases because the air gets thinner. As a result, you will have a lesser base (atmospheric pressure) therefore will make less boost overall due to this fact. Understand? 
