why do we have less boost when it is colder???
12-26-2003, 11:44 AM
#1
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why do we have less boost when it is colder???
can some one explain this phenomenon.
The temperatures was at or below freezing and I noticed that my boost gauge doesn't peak or hold at the levels that it used to when it was warmer.
I understand that a higher elevations, we also make less boost.
If someone could explain to me this theory in simple english, it would be much appreciated.
Thanks.
The temperatures was at or below freezing and I noticed that my boost gauge doesn't peak or hold at the levels that it used to when it was warmer.
I understand that a higher elevations, we also make less boost.
If someone could explain to me this theory in simple english, it would be much appreciated.
Thanks.
12-26-2003, 11:49 AM
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i believe it has something to do with colder air is more efficient so turbo's do not need to produce
as much boost to = same power -
am i far off on that? at least thats what I thought it was about. Something to do with air density and such - the turbos do not have to spin as hard to create the same power when the air is warmer and less dense
altitude = less boost more out of saftey for the turbos i believe and not such great tuning on the ecu quite often too.
am i far off on that? at least thats what I thought it was about. Something to do with air density and such - the turbos do not have to spin as hard to create the same power when the air is warmer and less dense
altitude = less boost more out of saftey for the turbos i believe and not such great tuning on the ecu quite often too.
12-26-2003, 11:55 AM
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interesting theory....
but I don't listen to hypothesis by Musicians, I want an physicist or an engineer. hehee.. just kidding Andy. Good assumption. I guess when you did notice less boost when you were up in Colorado right?
btw, was your car slower at higher elevations?
btw, was your car slower at higher elevations?
12-26-2003, 12:12 PM
#7
yes. simple.
people get so hung up on boost, when its really <b>MASS AIR FLOW</b> that the engine needs.
the relationship between pressure & volume & temp & mass air flow is described by the ideal gas law:
PV=nRT
nR == mass of air
P = pressure
V = volume
T = temp
mathematically the effect you witness happens because the computer holds the mass air flow constant and the intake tract volume is obviously contant. so the equation becomes pressure X constant = temp X constant. logically this means that as the temp decreases the pressure has to decrease in order for the equation to still be valid.
in simple terms, cold air is denser. and in cold weather the engine receives the same mass air as in warm weather, regardless of boost.
the relationship between pressure & volume & temp & mass air flow is described by the ideal gas law:
PV=nRT
nR == mass of air
P = pressure
V = volume
T = temp
mathematically the effect you witness happens because the computer holds the mass air flow constant and the intake tract volume is obviously contant. so the equation becomes pressure X constant = temp X constant. logically this means that as the temp decreases the pressure has to decrease in order for the equation to still be valid.
in simple terms, cold air is denser. and in cold weather the engine receives the same mass air as in warm weather, regardless of boost.
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12-26-2003, 12:23 PM
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The car is faster because the intake temps have dropped..
Why is that? At higher levels of boost the turbo gives off more heat, more heat in the air mix means less power..
The fact that the air is denser simply means that the turbos don't have to work as hard to get the same amount of air into the system.. Less work means less energy which means less heat omitted into the system..
The fact that the air is denser simply means that the turbos don't have to work as hard to get the same amount of air into the system.. Less work means less energy which means less heat omitted into the system..
12-26-2003, 12:26 PM
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yes S4's are "slower" at elevation - as are all turbo cars
not saying less power - just phsyically slower - the air is lense dense so it takes longer to make the same peak power - hence slower in a time line base - correct me if im wrong Eric or anyone - but the way i understand it is it takes longer to make the same power you would at sea level so the car is phsyically slower - near Vail I peaked at like 15-16psi and in Denver area it was more like 19 and in Boston it was more like 20-21