motox tech
Full Access Member
does the ambient temperature affect the atmospheric pressure?
Moose on the loose
- Thread starter motox tech
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funnyman06
Full Access Member
Yes, hot air is lighter, thats why in weather reports there are regions of high Pressure and Low Pressure. Thats also why when its really cold out you make more power...
FordGuy100
Registered User
Exactly, cooler air is more dense so you will be able to boost more, for more power.
motox tech
Full Access Member
So heres a monkey wrench for you. If I go over berthoud pass (about 30 min from here) Im gonna reach close to 12,000', when I drop off the backside into Denver im at a mile high, Hows much will twin turbos be affected by such dramatic altitude rollercoaster.(more important how will it affect motor)And am i gonna have to keep her at an idle when go to visit my dad in nebraska.
FordGuy100
Registered User
I believe so, I think he would need 30% more boost, if for anything else, the O2. If there is 30% less O2, which is the staple ingredient in a chemical burn of a carbo-hydrgren (that doesnt sound right, carbo hydrgen?). So along with the 4.24psi different gauge reading, he will need another 30% of boost to regain the O2 that is lost at higher elevations. So if we can run 10psi of boost on our gauges at sea level, he will need to run 18.512psi on his boost gauge to have the same amount of O2 in the engine for the same power as 10psi at sea level.
motox tech
Full Access Member
Hence---cold air induction, now im starting to savvy!!!
FordGuy100
Registered User
I think it will handle it. If you are going that much of elevation increase, and decreases I think a true twin setup (with 2 turbo's of the same size), might not be a good choice. If you stay at one general elevation you can size them to run at a certain boost, but if you go that much lower in elevation it might just cause some head gasket issues. If you run 20psi of boost up at 9000-12000', then it would be 24-25psi of boost down low and that just might be to much for the head gaskets to take.
I think a sequential turbo setup would work better, they seem more versitile to me.
FordGuy100
Registered User
Yes, the amount of O2 in 1cubic foot of air would be more if the air is cooler vs hotter. Its not air that you are wanting to compress, its the O2. Thats why nitrous is used in some racing applications because its basically injecting a gas that is high in oxygen.
funnyman06
Full Access Member
Alright lets do this.
Lets set up some fact to do our math by.
Temperature is constant for what i am doing. We all know its colder at 9000 feet, but for maths sake lets say its the same.
the equation for comparing gases is pv=nRt
P = the absolute pressure of the gas, in psi
n = number of moles, in lbmol
V = the volume of the gas, in ft3/lbmol
T = the absolute temperature of the gas absolute, in °R
R = the universal gas law constant of 10.7316 ft3·psi/(lbmol·°R)
we have 7.3L of air or 446 in^3.
Pressure is what we are changing
And everything on the right side is constant for what we are doing.
We will use a base of 446in^3 @ 14.7psi and compare all of our numbers to that.
446in^3 * 14.7psi = 6556.2
446in^3 * 10.46psi = 4665.16
again we see the 30% difference. Now in order to make up for the lost air we need to make 4.24lbs of boost. This is just right off the bat, right off idle you would have to make 4 lbs of boost to keep up.
Lets look at what happens when at sea level we are running at 14.7 lbs of boost.
446in^3 8 29.4psi = 13112.4
we have effectively doubled our displacement, back to 9000 ft.
in order to make the same amount of air we have to make almost 19psi of boost
446in^3 * (10.46psi + 18.94psi) = 13112.4
So it would seem you need to make about 4.25 extra lbs of boost than the rest of us at 9000 feet, all the time. So you are really looking to make boost somewhere in the range of 5psi to almost 23psi depending on how much equivalent boost you want to make.
I think this makes sense
Lets set up some fact to do our math by.
Temperature is constant for what i am doing. We all know its colder at 9000 feet, but for maths sake lets say its the same.
the equation for comparing gases is pv=nRt
P = the absolute pressure of the gas, in psi
n = number of moles, in lbmol
V = the volume of the gas, in ft3/lbmol
T = the absolute temperature of the gas absolute, in °R
R = the universal gas law constant of 10.7316 ft3·psi/(lbmol·°R)
we have 7.3L of air or 446 in^3.
Pressure is what we are changing
And everything on the right side is constant for what we are doing.
We will use a base of 446in^3 @ 14.7psi and compare all of our numbers to that.
446in^3 * 14.7psi = 6556.2
446in^3 * 10.46psi = 4665.16
again we see the 30% difference. Now in order to make up for the lost air we need to make 4.24lbs of boost. This is just right off the bat, right off idle you would have to make 4 lbs of boost to keep up.
Lets look at what happens when at sea level we are running at 14.7 lbs of boost.
446in^3 8 29.4psi = 13112.4
we have effectively doubled our displacement, back to 9000 ft.
in order to make the same amount of air we have to make almost 19psi of boost
446in^3 * (10.46psi + 18.94psi) = 13112.4
So it would seem you need to make about 4.25 extra lbs of boost than the rest of us at 9000 feet, all the time. So you are really looking to make boost somewhere in the range of 5psi to almost 23psi depending on how much equivalent boost you want to make.
I think this makes sense
FordGuy100
Registered User
I agree that will bring you back up to the realitive pressure within the engine...will it compensate for the O2 lost at higher elevations?
funnyman06
Full Access Member
Well i am pretty sure that the amount of o2 is directly proportional the the atmospheric pressure. So more pressure, more o2
FordGuy100
Registered User
I was thinking the same thing as well as I thought of it.
Quick research comes up as you are correct
funnyman06
Full Access Member
Go us!
FordGuy100
Registered User
funnyman06
Full Access Member
And now we know why we now have wastegated turbos
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