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Discussion Starter · #1 ·
I noticed this a while ago, but never got around to asking the question.

On the AP, there is the option to monitor "boosted temp". first off, I assume this is the temp of the air after the turbocharger (air is boosted).

Can anyone explain to me why the temp actually goes DOWN when I go into boost? The air is compressed so it should heat up. My only ideas is,

1. it has something to do with sucking in all the hot engine air then pulling in the cool ambient air...and temp goes down.

2. Something with the intercooler being able to cool the air better when a large amount of air is flowing through it.




Also, anyone know the temp where pre-det can start to occur due to the extremely hot intake temp?
 

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Yea I have noticed the same thing on my DH. I guess its cos its pulling more fresh cold air through the intake as opposed to measuring the heat soaked air. You still see its hot though. It never reaches the intake air temp. Mine is around 30 degrees more that intake air temp
 

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The boost air temp sensor is located in the intake manifold so after the throttle plate.

The temps go cooler when you are in boost because the throttle plate is open more allowing more cooler air to enter.
Also, since it is in the intake manifold I think the temperature of the engine itself has an effect on the boosted air temp, especially at idle or low throttle driving.....
 

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Discussion Starter · #4 ·
[quote author=timv link=topic=135357.msg2913311#msg2913311 date=1233804058]
The boost air temp sensor is located in the intake manifold so after the throttle plate.

The temps go cooler when you are in boost because the throttle plate is open more allowing more cooler air to enter.
Also, since it is in the intake manifold I think the temperature of the engine itself has an effect on the boosted air temp, especially at idle or low throttle driving.....

[/quote]

When the throttle plate opens it doesnt let "cool air" in...it lets compressed air in. Compressed air...and when air is compressed it gets hotter.
 

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I'll give y'all a hint:

The BAT (Boost Air Temperature) sensor is "shared" (i.e. the same physical location) with the MAP (Manifold Absolute Pressure) sensor.
 

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For those of us with the AP,

What temps are you guys getting, I'm wondering what the difference is between us TMIC guys and those that are FMIC...?
 

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I think I can answer this.

This has to do with heat exchanger (intercooler) theory. Basically pressure helps the exchange of heat between your intercooler and the air.

So lets say you are driving for a few minutes and your engine bay has heated up. This will heat up your intercooler pipes and manifolds, but not your intercooler as much because it is getting access to ambient cooler air.

Now you are at part throttle and the air going through your intake system is going thru slow because you are not flowing much air. This slower air has more time to heat up due to the intercooler pipes manifold and intake system. At the same time the intercooler has less effect on cooling because the air that is passing thru it is not boosted air.

Heat exchangers (intercooler) will work more efficiently the more mass air is going thru them and will work better when the air is under pressure. This pressure will cause friction between the intercooler fin walls and the air providing a good amount of exchanged heat from the air to the intercooler heat sink.

So when you are at part throttle, your air is getting heated by the intercooler pipes and manifold at the same time your intercooler is not really doing much, that will result in higher temps.

Now lets say you go into boost. Although your turbo is now producing warmer air, your boosted air is going thru the intake pipes and intercooler faster and under pressure, so the pipes and manifold will have less of an effect in heating the air. At the same time this massive (boosted) air slug will effecively "kick in" the intercooler; this pressure will cause friction between the fins and air and remove the heat from the air. This temperature will be lower because your intercooler is cooler than the intercooler pipes and manifold. Now if you stay in boost eventually you will heat soak your intercooler, but initially you should see a drop in boost temps.
 

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Discussion Starter · #9 ·
[quote author=BellaBeagle link=topic=135357.msg2919474#msg2919474 date=1234018045]
I think I can answer this.

This has to do with heat exchanger (intercooler) theory. Basically pressure helps the exchange of heat between your intercooler and the air.

So lets say you are driving for a few minutes and your engine bay has heated up. This will heat up your intercooler pipes and manifolds, but not your intercooler as much because it is getting access to ambient cooler air.

Now you are at part throttle and the air going through your intake system is going thru slow because you are not flowing much air. This slower air has more time to heat up due to the intercooler pipes manifold and intake system. At the same time the intercooler has less effect on cooling because the air that is passing thru it is not boosted air.

Heat exchangers (intercooler) will work more efficiently the more mass air is going thru them and will work better when the air is under pressure. This pressure will cause friction between the intercooler fin walls and the air providing a good amount of exchanged heat from the air to the intercooler heat sink.

So when you are at part throttle, your air is getting heated by the intercooler pipes and manifold at the same time your intercooler is not really doing much, that will result in higher temps.

Now lets say you go into boost. Although your turbo is now producing warmer air, your boosted air is going thru the intake pipes and intercooler faster and under pressure, so the pipes and manifold will have less of an effect in heating the air. At the same time this massive (boosted) air slug will effecively "kick in" the intercooler; this pressure will cause friction between the fins and air and remove the heat from the air. This temperature will be lower because your intercooler is cooler than the intercooler pipes and manifold. Now if you stay in boost eventually you will heat soak your intercooler, but initially you should see a drop in boost temps.


[/quote]

now assuming that is all true (im not calling you a liar...but lets face it...everyone claims they are an expert on the internet lol), that would make sense and it answers my question.

This is quiet an interesting topic for me...I should ask the instructor that is in charge of my aviation systems class (hes a A&P examiner) and see what he thinks.
 

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[quote author=BellaBeagle link=topic=135357.msg2919474#msg2919474 date=1234018045]
I think I can answer this.

This has to do with heat exchanger (intercooler) theory. Basically pressure helps the exchange of heat between your intercooler and the air.

So lets say you are driving for a few minutes and your engine bay has heated up. This will heat up your intercooler pipes and manifolds, but not your intercooler as much because it is getting access to ambient cooler air.

Now you are at part throttle and the air going through your intake system is going thru slow because you are not flowing much air. This slower air has more time to heat up due to the intercooler pipes manifold and intake system. At the same time the intercooler has less effect on cooling because the air that is passing thru it is not boosted air.

Heat exchangers (intercooler) will work more efficiently the more mass air is going thru them and will work better when the air is under pressure. This pressure will cause friction between the intercooler fin walls and the air providing a good amount of exchanged heat from the air to the intercooler heat sink.

So when you are at part throttle, your air is getting heated by the intercooler pipes and manifold at the same time your intercooler is not really doing much, that will result in higher temps.

Now lets say you go into boost. Although your turbo is now producing warmer air, your boosted air is going thru the intake pipes and intercooler faster and under pressure, so the pipes and manifold will have less of an effect in heating the air. At the same time this massive (boosted) air slug will effecively "kick in" the intercooler; this pressure will cause friction between the fins and air and remove the heat from the air. This temperature will be lower because your intercooler is cooler than the intercooler pipes and manifold. Now if you stay in boost eventually you will heat soak your intercooler, but initially you should see a drop in boost temps.


[/quote]

Nice try but...

Consider what the BAT sensor is "seeing" when there is no boost (i.e. when the intake manifold pressure is not greater than atmospheric pressure).
 

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[quote author=GT1 link=topic=135357.msg2920078#msg2920078 date=1234042886]
[quote author=BellaBeagle link=topic=135357.msg2919474#msg2919474 date=1234018045]
I think I can answer this.

This has to do with heat exchanger (intercooler) theory. Basically pressure helps the exchange of heat between your intercooler and the air.

So lets say you are driving for a few minutes and your engine bay has heated up. This will heat up your intercooler pipes and manifolds, but not your intercooler as much because it is getting access to ambient cooler air.

Now you are at part throttle and the air going through your intake system is going thru slow because you are not flowing much air. This slower air has more time to heat up due to the intercooler pipes manifold and intake system. At the same time the intercooler has less effect on cooling because the air that is passing thru it is not boosted air.

Heat exchangers (intercooler) will work more efficiently the more mass air is going thru them and will work better when the air is under pressure. This pressure will cause friction between the intercooler fin walls and the air providing a good amount of exchanged heat from the air to the intercooler heat sink.

So when you are at part throttle, your air is getting heated by the intercooler pipes and manifold at the same time your intercooler is not really doing much, that will result in higher temps.

Now lets say you go into boost. Although your turbo is now producing warmer air, your boosted air is going thru the intake pipes and intercooler faster and under pressure, so the pipes and manifold will have less of an effect in heating the air. At the same time this massive (boosted) air slug will effecively "kick in" the intercooler; this pressure will cause friction between the fins and air and remove the heat from the air. This temperature will be lower because your intercooler is cooler than the intercooler pipes and manifold. Now if you stay in boost eventually you will heat soak your intercooler, but initially you should see a drop in boost temps.


[/quote]

Nice try but...

Consider what the BAT sensor is "seeing" when there is no boost (i.e. when the intake manifold pressure is not greater than atmospheric pressure).
[/quote]

Its reading the temps in the manifold.

What is this?
Mother may I?
If you freaken know something.... THEN SAY IT! :blah:
 

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[quote author=BellaBeagle link=topic=135357.msg2921178#msg2921178 date=1234082397]
[quote author=GT1 link=topic=135357.msg2920078#msg2920078 date=1234042886]
[quote author=BellaBeagle link=topic=135357.msg2919474#msg2919474 date=1234018045]
I think I can answer this.

This has to do with heat exchanger (intercooler) theory. Basically pressure helps the exchange of heat between your intercooler and the air.

So lets say you are driving for a few minutes and your engine bay has heated up. This will heat up your intercooler pipes and manifolds, but not your intercooler as much because it is getting access to ambient cooler air.

Now you are at part throttle and the air going through your intake system is going thru slow because you are not flowing much air. This slower air has more time to heat up due to the intercooler pipes manifold and intake system. At the same time the intercooler has less effect on cooling because the air that is passing thru it is not boosted air.

Heat exchangers (intercooler) will work more efficiently the more mass air is going thru them and will work better when the air is under pressure. This pressure will cause friction between the intercooler fin walls and the air providing a good amount of exchanged heat from the air to the intercooler heat sink.

So when you are at part throttle, your air is getting heated by the intercooler pipes and manifold at the same time your intercooler is not really doing much, that will result in higher temps.

Now lets say you go into boost. Although your turbo is now producing warmer air, your boosted air is going thru the intake pipes and intercooler faster and under pressure, so the pipes and manifold will have less of an effect in heating the air. At the same time this massive (boosted) air slug will effecively "kick in" the intercooler; this pressure will cause friction between the fins and air and remove the heat from the air. This temperature will be lower because your intercooler is cooler than the intercooler pipes and manifold. Now if you stay in boost eventually you will heat soak your intercooler, but initially you should see a drop in boost temps.


[/quote]

Nice try but...

Consider what the BAT sensor is "seeing" when there is no boost (i.e. when the intake manifold pressure is not greater than atmospheric pressure).
[/quote]

Its reading the temps in the manifold.

What is this?
Mother may I?
If you freaken know something.... THEN SAY IT! :blah:
[/quote]

bellabeagle's theory is correct. the pressurized air cools more efficiently as it goes through the intercooler than non pressurized air.
 

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[quote author=BellaBeagle link=topic=135357.msg2921178#msg2921178 date=1234082397]
[quote author=GT1 link=topic=135357.msg2920078#msg2920078 date=1234042886]
[quote author=BellaBeagle link=topic=135357.msg2919474#msg2919474 date=1234018045]
I think I can answer this.

This has to do with heat exchanger (intercooler) theory. Basically pressure helps the exchange of heat between your intercooler and the air.

So lets say you are driving for a few minutes and your engine bay has heated up. This will heat up your intercooler pipes and manifolds, but not your intercooler as much because it is getting access to ambient cooler air.

Now you are at part throttle and the air going through your intake system is going thru slow because you are not flowing much air. This slower air has more time to heat up due to the intercooler pipes manifold and intake system. At the same time the intercooler has less effect on cooling because the air that is passing thru it is not boosted air.

Heat exchangers (intercooler) will work more efficiently the more mass air is going thru them and will work better when the air is under pressure. This pressure will cause friction between the intercooler fin walls and the air providing a good amount of exchanged heat from the air to the intercooler heat sink.

So when you are at part throttle, your air is getting heated by the intercooler pipes and manifold at the same time your intercooler is not really doing much, that will result in higher temps.

Now lets say you go into boost. Although your turbo is now producing warmer air, your boosted air is going thru the intake pipes and intercooler faster and under pressure, so the pipes and manifold will have less of an effect in heating the air. At the same time this massive (boosted) air slug will effecively "kick in" the intercooler; this pressure will cause friction between the fins and air and remove the heat from the air. This temperature will be lower because your intercooler is cooler than the intercooler pipes and manifold. Now if you stay in boost eventually you will heat soak your intercooler, but initially you should see a drop in boost temps.


[/quote]

Nice try but...

Consider what the BAT sensor is "seeing" when there is no boost (i.e. when the intake manifold pressure is not greater than atmospheric pressure).
[/quote]

Its reading the temps in the manifold.

What is this?
Mother may I?
If you freaken know something.... THEN SAY IT! :blah:
[/quote]

OK...

Considering that the BAT sensor is a temperature sensor that relies on convection, it can't work very well in a vacuum, now can it?

The temperature increase when there is no boost (i.e. when the manifold pressure is less than atmospheric) is a result of the direct conduction of heat from the (hot) engine to the BAT sensor.

Simply put, the BAT readings are invalid unless there is boost.
 

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[quote author=GT1 link=topic=135357.msg2926123#msg2926123 date=1234252467]
OK...

Considering that the BAT sensor is a temperature sensor that relies on convection, it can't work very well in a vacuum, now can it?

The temperature increase when there is no boost (i.e. when the manifold pressure is less than atmospheric) is a result of the direct conduction of heat from the (hot) engine to the BAT sensor.

Simply put, the BAT readings are invalid unless there is boost.
[/quote]

Good observation. But I wouldn't call them "invalid". Substantially less accurate, maybe, but unless you have a model or data showing the contributiong of radiated/conducted heat vs. convected heat for a given air mass flow, then we really can't be sure.

I'm willing to bet it's a combination of this theory as well as the HX efficiency theory, which btw, has as much to do with the air's velocity as the air's density. All heat exchangers, regardless of the working fluids, are roughly an order of magnitude more efficient when said fluids are under turbulent flow vs. laminar.
 

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[quote author=GT1 link=topic=135357.msg2926123#msg2926123 date=1234252467]

OK...

Considering that the BAT sensor is a temperature sensor that relies on convection, it can't work very well in a vacuum, now can it?

The temperature increase when there is no boost (i.e. when the manifold pressure is less than atmospheric) is a result of the direct conduction of heat from the (hot) engine to the BAT sensor.

Simply put, the BAT readings are invalid unless there is boost.

[/quote]

At a high vacuum, a thermocouple will not read temperature. Just as 'nothingness' has no color, taste, smell, etc. it also has no temperature. Therefore, if you put a thermocouple in a vacuum it will continue to read the previous (this is important) temperature unless heat is transferred by radiation. A thermocouple "in a vacuum" will be in thermal equilibrium with the electromagnetic radiation field surrounding it. The thermocouple will not go down or up due to the lack of air. Therefore, the only thing to make the thermocouple change its reading, is air; I don't think the effect of electromagnetic radiation has any significant effect in your intake manifold.

So lets think about what is happening in the manifold. You are driving along not really into boost but certainly not at vacuum. So air is passing over the thermocouple. After all how could your car be even idling if there is no air mass traveling into the engine. Then you hit boost. Now what has been observed is that the BAT sensor is registering a higher reading during this whole time during part throttle. Then when you initially hit boost the temps drop. This has nothing to do with vacuum because first you were not in vacuum and second even if you were, the thermocouple would read its last reading and not go up randomly as you have implied.

I have noticed (just like what the op has reported) that the BAT is reading higher temps when in partial throttle (not vacuum), but when I initially go into boost the temps drop. Further, if we did see a vacuum, the temps would not go up or down, they would read the last measurement.

So I think unless you can come up with something else, I do not think the vacuum theory explains this observation.
 

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[quote author=BellaBeagle link=topic=135357.msg2927497#msg2927497 date=1234303508]
At a high vacuum, a thermocouple will not read temperature. Just as 'nothingness' has no color, taste, smell, etc. it also has no temperature. Therefore, if you put a thermocouple in a vacuum it will continue to read the previous (this is important) temperature unless heat is transferred by radiation. A thermocouple "in a vacuum" will be in thermal equilibrium with the electromagnetic radiation field surrounding it. The thermocouple will not go down or up due to the lack of air. Therefore, the only thing to make the thermocouple change its reading, is air; I don't think the effect of electromagnetic radiation has any significant effect in your intake manifold.

So lets think about what is happening in the manifold. You are driving along not really into boost but certainly not at vacuum. So air is passing over the thermocouple. After all how could your car be even idling if there is no air mass traveling into the engine. Then you hit boost. Now what has been observed is that the BAT sensor is registering a higher reading during this whole time during part throttle. Then when you initially hit boost the temps drop. This has nothing to do with vacuum because first you were not in vacuum and second even if you were, the thermocouple would read its last reading and not go up randomly as you have implied.

I have noticed (just like what the op has reported) that the BAT is reading higher temps when in partial throttle (not vacuum), but when I initially go into boost the temps drop. Further, if we did see a vacuum, the temps would not go up or down, they would read the last measurement.

So I think unless you can come up with something else, I do not think the vacuum theory explains this observation.
[/quote]

Partial throttle is vacuum, relative to ambient, and relative further to WOT/boost. That's the whole point. Anywhere between idle and WOT at full boost, we're talking a difference in absolute pressure of ~25-30psi. In a percentage scale of mass flow at WOT/boost over idle, it nears a thousand. So when we're comparing the three methods of heat transfer, convection/radiation/conduction, one has to think a change in one variable, i.e. convection, of several orders of magnitude over the range of operation is DAMN significant. Thus the vacuum theory likely explains a significant portion of this phenomenon... Not to mention changing laminar vs. turbulent flow charictaristics around the BAT itself under varying MAF, which is related to the HX efficiency theory to which I also believe is a contributing factor.

That's all to say I disagree with you. :)
 

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You are missing my point. Did you read my post? If there is a vacuum or not... it does not matter.

Again, If you put a thermocouple in a vacuum it will continue to read the previous (this is important) temperature unless heat is transferred by radiation. A thermocouple "in a vacuum" will be in thermal equilibrium with the electromagnetic radiation field surrounding it. The thermocouple will not go down or up due to the lack of air. Although less mass air may decrease the rate of change of the thermocouple it will not randomly change the direction.

So how do you explain a lack of air increasing the BAT temps?

And, it is not a true vacuum. Actually a true vacuum is impossible there is always something there. At part throttle I measure roughly -5 HG to 2 psi. This is near 1 atm and is hardly a vacuum and certainly enough to affect a thermocouple regardless of the flow. Air does not need to be moving at all to register a temperature on a thermocouple.

Surely you can not be saying that we drive around all day part throttle with no air in our intake tract unless we are at boost. The car would not run much less even idle :lol:

But again that is all beside the point... The fact is that vacuums do not randomly increase temperatures, or decrease them. So this can not be the reason for the increased BAT.
 

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Truly, I am not arguing for the sake of arguement here. And my apologies if I come across as anything but salient and objective. But I think you are quoting basics of simple thermal fluid transfer without grasping the whole picture.

I see my response to you was arguing against a point you essentially weren't making, my apologies. But preceding that, your arguement was against a point no one else here has made either. Your point is moot, because no one here is arguing convective heat transfer takes place in an absolute vacuum. Rather, our description of vacuum is really describing manifold pressure (or lack thereof) on the vacuum side of the gauge, i.e. anything below ambient pressure, i.e. anything less than what a NA engine could produce at 100% volumetric efficiency.

To quote you and attempt to dissect your misunderstanding, "So how do you explain a lack of air increasing the BAT temps?".

As I've described all along, there are two other modes of heat transfer, radiation and conduction. Both will change the thermocouple's reading regardless of state of ambient pressure. As long as these other modes of heat transfer are available to said thermocouple, which they should be... especially in a vacuum, they will have a great deal of influence on the thermocouple's output. In other words, change in temperature due to radiative and conductive heat transfer is a simple/common occurance, both of which occur all the time in a "lack of air" environment.

The point is this: the relative difference in convective heat transfer is very, very significant between idle and full boost. Enough to substantially contribute to the phenomenon in question. And we have been describing it all along as vacuum vs. non vacuum. So what?
 

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I am not trying to argue either. And I respect your opinions. And I am actually tired of this conversation. I am sure any idiot who is actually still reading our labored posts is rather bored out of their freaking mind or is a crazed geeky lunatic. But anyway...

Basically I do not agree with your post. I am not sure you are thinking this through. I have offered what I still maintain to be the best explanation for the observed data. I still maintain that this is a result of the intercooler and not a probe malfunction due to less air. You can read my previous post. Please do. I have layed out specifically how and why this makes sense with an actual example. Also I have layed out an example of how and why the vacuum would not cause this and how the manifold is not actually a high vacuum. Further if you have a dashawk you should observe this effect for yourself.

Anyway the vacuum theory does not make sense because:

ONLY VACUUMS WITH LESS THAN 1 TORR WILL HAVE ANY AFFECT ON REDUCING THERMOCONDUCTIVITY. As it turns out, the thermal conductivity of air is nearly constant down to a fairly low pressure - about 1 Torr. Then it begins to change rather linearly with pressure down to a value of about 1 mTorr, whereupon conduction through the gas ceases to be a major factor. At that point, the dominant loss factor will be radiation.

Do you know what 1 torr is?? The torr (symbol: torr), defined as 1/760 atm exactly. That is very very little air. This is not what is going on in our manifold. If you think it is... You are wrong. I am sorry to be blunt but we have more than 1/760 atm in our manifold at all times. Even if you are going down a long hill 80mph in 1st gear. :lol:

It is pretty close to a perfect vacuum. And when I say vacuum I don't mean anything that is under 1 atm. I mean litterally a vacuum where there is virtually no matter.

I really think you need to do more research.

And if you observe the affect on the Dashawk the BAT temps will be at say 80 degrees when I am crusing on the highway at 0-1 psi (again no vacuum). Then I hit the gas and go into boost the temps drop. Nowhere in that example is there a vacuum that the sensor is seeing. And certainly not the kind of vacuum you need to switch off convection. You should observe the affect and you will see.. It will make sense.

[quote author=Nikolai link=topic=135357.msg2928338#msg2928338 date=1234324384]
To quote you and attempt to dissect your misunderstanding, "So how do you explain a lack of air increasing the BAT temps?".

As I've described all along, there are two other modes of heat transfer, radiation and conduction. Both will change the thermocouple's reading regardless of state of ambient pressure. As long as these other modes of heat transfer are available to said thermocouple, which they should be... especially in a vacuum, they will have a great deal of influence on the thermocouple's output. [/quote]

No..
Conduction is heat transferred from one material to another by direct contact by definition. There is nothing in contact with the thermocouple's sensory junction. Therefore, conduction has nothing to do with this.
 
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