[Overboost]

Lately I have been seeing a lot of threads popping up on the differences between DCI and the stock box or cold air intakes. I cannot give an answer as to which one is better as I think it is quite conditional of the environment factors, temperature being the most obvious. It is better to understand the affects of temperature in terms of energy transfer. I for one would choose the the intake with lower temps if the subsequent increase in duty cycles is not so great lets say 2-3%.

Would be helpful if tuners such as Shiv, Mike/Terry and Rob can chime in on this too.

One thing to understand before reading this is:
The specific heat capacity of a substance is the quantity of heat energy required to change the state of a unit mass of a substance or in layman's terms, to raise its temperature.



Fact 1
Fact one is to clarify the myth that "the inlet temperature does not matter because the Turbos will heat it up".

While this is somewhat true, some people are under the understanding that the turbo will make them the same temperature. This is false.
To explain this we will create the scenario of holding the turbo rpm constant and assuming that both types of intake will run the same duty cycle at the same boost pressure. (This is not always the case).

At a constant rpm the amount of heat energy released from the turbo will be the same under identical environmental conditions. Therefore if the inlet air is 8 degrees cooler it should be about 8 degrees cooler after leaving the compressor wheel. I say about 8 degrees cooler just to make things easier to understand. In reality as the temperature decreases, the specific heat capacity of air increases which means it takes more energy to raise it 1 degree).


Fact 2
Increasing the flow of air does not necessarily increase horsepower especially if there is an increase in inlet temperature.

Oxygen in the air is the element needed for combustion. At atmospheric pressure of 1 bar oxygen content is only approximately 21% of the air composition, nitrogen being 78% and carbon dioxide as well as a few other elements making up the rest. These ratios change somewhat as temperature changes (oxygen content increasing as temperature decreases).

As temperature increases, atoms gain more energy and the volume of space that each atom occupies increases making the charge air less dense.

We can think of this as a house hold full of kids. During the day when the sun is out, they are full of energy and run around the house and you can't keep track of them all in one area. When they become hungry or tired as they lose energy they all gather around the dinner table or bedroom to rest.

The only problem we face in this scenario is that with a decrease in flow, we also see and increase in wastegate duty cycles which is indicative of higher turbine speeds and an increase in the release of heat energy. How much so is really hard to quantify. This is where post turbine IAT would be useful.

Fact 3

The third thing I always hear is that "inlet temps do not matter because the intercooler will cool it down".

The fact here is that the intercooler is a constant mass of metal. Therefore given identical environmental condition it will remove the same amount of heat energy from any mass of air. Where we see a difference here is that the latent heat capacity of the intercooler will decrease as the metal heat soaks. A higher temperature of air entering the intercooler will obviously heat soak the intercooler faster, reducing its efficiency.

Its hard to draw conclusion from a lot of the datalogs being posted here simply because cooling capacity of an intercooler changes with factors such as temperature, humidity and atmospheric pressure.

As temperature decreases, intercooler efficiency increases somewhat exponentially.

I haven't scientifically proven this but I would think that as humidity increases, intercooler efficiency also increases. This is due to water having a higher specific heat capacity than air which will remove more heat from the intercooler core. So although datalogs are being provided with near identical temperarutes, if the humidity varies then the results are skewed.

As atmospheric pressure increases as you get closer to sea level, intercooler efficiency as well as engine volumetric efficiency will increase. Intercooler efficiency increases because latent heat capacity increases as density of air increases.

Fact 4
An interesting fact that I gathered from my readings is that for every 10 F increase in temperature, the engine octane requirement is increased by approximately 0.5 octane. In other words it becomes slightly more prone to detonation.


Many of you know this information already but there still are a lot of misinformed people on the forum. I have a bachelors of science degree and if it wasn't for my love of cars and being able to correlate what I learned with my car, I probably would have failed chemistry and physics. I got A's by the way lol.

I just moved to Florida from Kentucky and I'm about to change from an DCI to a closed box system for two reasons. The first being, I noticed that after sitting at a stop light here for 3 mins my rpm will drop for a brief second as my intake temps increase exponentially. The second reason being my injen intake does not fit quite well with the vishnu PWM meth. I will probably do datalogs of both to see which type of intake is the best overall performing both daily driving and WOT for the conditions here in Florida.

Guys feel free to chime in with any information I may have left out.

[rismo]

Great wrap up! Thx

[vasillalov]

NICE!

Some additional information concerning air and air density:

The colder the air, the higher the density.
The hotter the air, the lower the density.

Air at 30 degrees centigrade (hot summer day) has density of about 1.1644 kg/m3
Air at -20 degrees centigrade (cold winter morning) has density of about 1.3943 kg/m3

So basically this means that there is about 17% difference in air density between a hot summer day and a cold winter morning.

Source: http://en.wikipedia.org/wiki/Air_density

What does that mean:

Well, the molecular "ingredients" of air are the same regardless of the temperature (unless we are talking about extremes here). This means that the ratio between the components of which air is made of is the same: 78% Nitrogen, 21% Oxygen and the rest is just CO2, water vapor and human farts.

When you have denser air, you basically have MORE air in a cubic foot of space. In other words: colder air = more oxygen per unit volume. This means that with colder air, you will have MORE oxygen entering the combustion chamber. This will inevitably be picked up by the O2 sensors which act as snitches for the DME. The DME will detect this higher oxygen condition and will ADD fuel to get to a proper A/F ratio.

More fuel + more oxygen = more Power!

[Bmwguy11]

Actually, the hotter the air, the more the intercooler will cool the air. Intercoolers cool by a percentage, and that is how their efficiency is measured. So air that is 600 degrees going into the intercooler vs 500 degrees into the intercooler, the 600 degree air will have a greater delta in temperature change. This greatly reduces the initial 100 degree difference between the two.

edit: correction, the hotter the air before turbo, the slightly more the turbo compression process will increase that difference. But the intercooler difference is greater.

[gboop]

A bunch of facts, but no cohesive empirical evidence.
I would like to hear the FACTS for below:

1. How much HP is a 7-10 degree cooler intake temp worth for same volume?
2. How much HP is lost by using a restrictive intake with cooler air but not enough volume for high horsepower application?
3. Does removing a restriction with DCI positively offset the losses caused by higher intake temps?

[dzenno]

Cool write up and I agree with everything you've posted...wow, that doesn't happen every day on here lol

[vasillalov]

Originally Posted by Bmwguy11

Actually, the hotter the air, the more the intercooler will cool the air. ... But the intercooler difference is greater.

Agreed! But we are not looking for the largest delta of cooling as an end result. We are looking for LOWEST temperatures at the manifold coupled with high flow! The two do not necessarily go hand in hand.

[Bmwguy11]

I found some old formulas, so let me demonstrate.

All formulas below are assuming 80% efficiency turbos, 12 PSI input pressure and 14 PSI output pressure, and 80 degree outside (ambient) air temp. Also using 80% efficiency IC, and 1 PSI loss through the IC.

100 degree intake temp (pre turbo) =
Turbo outlet temp = 271 degrees F.
After IC temp = 118 degrees.

110 degree intake temp (pre turbo) =
turbo outlet temp = 284 degrees F.
After IC temp = 121 degrees F.


So, as you can see, a 10 degree difference from the intake temp pre-turbo, eventually equated to only a 3 degree temp difference IAT. So yes, it does matter that these cars are forced induction and have intercoolers. This is why FI cars tend to not have as much problems with ambient/intake air temp compared to say NA cars. It is not a linear temperature difference from pre-turbo to after-turbo to after-IC.

[Bmwguy11]

Originally Posted by vasillalov

Agreed! But we are not looking for the largest delta of cooling as an end result. We are looking for LOWEST temperatures at the manifold coupled with high flow! The two do not necessarily go hand in hand.

The OP didn't discuss differences in volume/flow. He said "all other things being equal", which is sort of a fallacy in and of itself since that's not how it will ever work in the real world. But, using his "all other things being equal" I just posted what a 10 degree intake temp difference would equate to at the IAT, using the numbers/factors I posted.

[rismo]

But this last one will also depend on the efficiency of the IC and the type of turbo´s - engine config, I assume....

[Joshboody]

VE actually decreases with pressure, but mass airflow increases.

2 to 3% is quite a lot for WGDC… of course the actual pressure ratio would be better comparison. I do think DCI are adding more heat, but the reduced PR means similar IC inlet temps. If it’s the same IAT, then then DCI give higher boost ceiling.

I thought IC efficiency percentage was fairly steady, and not sure about the humidity aspect, but I know it’s easier to extract or add heat with dryer air generally speaking.

I’m in the same boat trying to decide.

[vasillalov]

Originally Posted by Bmwguy11

I found some old formulas, so let me demonstrate.

All formulas below are assuming 80% efficiency turbos, 12 PSI input pressure and 14 PSI output pressure, and 80 degree outside (ambient) air temp. Also using 80% efficiency IC, and 1 PSI loss through the IC.

100 degree intake temp (pre turbo) =
Turbo outlet temp = 271 degrees F.
After IC temp = 118 degrees.

110 degree intake temp (pre turbo) =
turbo outlet temp = 284 degrees F.
After IC temp = 121 degrees F.


So, as you can see, a 10 degree difference from the intake temp pre-turbo, eventually equated to only a 3 degree temp difference IAT. So yes, it does matter that these cars are forced induction and have intercoolers. This is why FI cars tend to not have as much problems with ambient/intake air temp compared to say NA cars. It is not a linear temperature difference from pre-turbo to after-turbo to after-IC.

Agreed! That's not a problem here. We all understand that. Its just that the cooler intake air still produced cooler manifold air temperature, which ultimately makes more power.

An interesting twist of all this: by improving the efficiency of the intercooler and the plumbing, you are improving the linearity of the temperature difference pre-turbo and after-IC. In other words:

1. Start with the coolest air possible
2. Maximize the benefits of that by improving the intercooler efficiency.

Do not use 1 and 2 as substitutes for each other. Use them in conjunction! I think this is where a lot of people get caught up.

[Bmwguy11]

Originally Posted by vasillalov

Agreed! That's not a problem here. We all understand that. Its just that the cooler intake air still produced cooler manifold air temperature, which ultimately makes more power.

An interesting twist of all this: by improving the efficiency of the intercooler and the plumbing, you are improving the linearity of the temperature difference pre-turbo and after-IC. In other words:

1. Start with the coolest air possible
2. Maximize the benefits of that by improving the intercooler efficiency.

Do not use 1 and 2 as substitutes for each other. Use them in conjunction! I think this is where a lot of people get caught up.

Do you know how much more power a mere 3 degree air temperature makes? I mean, it's the definition of splitting hairs at that point... If you are trying to tune for every last fraction of a horsepower you can get, then sure, worry your head to death about number 1. However, I'd guess that 99% of the users of this forum don't care about fractions of horsepower gains. And remember that these numbers don't even take into account the increased air flow from DCI.



That said, let me improve the IC efficiency to 85%, all other things the same with the scenario I posted above, and we get this:


100 degree intake temp (pre turbo) =
Turbo outlet temp = 271 degrees F.
After IC temp = 109 degrees.

110 degree intake temp (pre turbo) =
turbo outlet temp = 284 degrees F.
After IC temp = 111 degrees F.



Interesting to note that IC efficiency increase of only 5% netted a very nice temperature drop from 80% efficiency. Though it also reduced the effect of the intake air temperature difference from 3 degrees IAT to 2 degrees IAT. So, point of note, the more you increase IC efficiency, the less intake air temp matters.

[vasillalov]

Originally Posted by Bmwguy11

Do you know how much more power a mere 3 degree air temperature makes? I mean, it's the definition of splitting hairs at that point...

Agreed. At no point I am arguing! That's a thread about FACTS so that's what I stated. I agreed with everything you said.

EDIT: 90% intercooler efficiency? Who makes one?

[Bmwguy11]

Originally Posted by Overboost

Fact 1
Fact one is to clarify the myth that "the inlet temperature does not matter because the Turbos will heat it up".

While this is somewhat true, some people are under the understanding that the turbo will make them the same temperature. This is false.
To explain this we will create the scenario of holding the turbo rpm constant and assuming that both types of intake will run the same duty cycle at the same boost pressure. (This is not always the case).

At a constant rpm the amount of heat energy released from the turbo will be the same under identical environmental conditions. Therefore if the inlet air is 8 degrees cooler it should be about 8 degrees cooler after leaving the compressor wheel. I say about 8 degrees cooler just to make things easier to understand. In reality as the temperature decreases, the latent heat capacity of air increases which means it takes more energy to raise it 1 degree).

This is definitely NOT a "fact". That's not how it works.

http://www.roymech.co.uk/Related/The...html#rot_turbo

[Overboost]

Originally Posted by Bmwguy11

This is definitely NOT a "fact". That's not how it works.

http://www.roymech.co.uk/Related/The...html#rot_turbo

Obviously it doesn't work like this in real life because we would never be able to keep wastegate duty cycle and turbo rpm or environmental conditions constant. If we could then the heat energy given off by the turbos will be constant and the increase in temps would be also be somewhat constant since change in heat capacity is not that much at a delta of a few degrees. Take everything i say in the context it was given please.

Friction and inertia etc would come in to play in this but again i said keeping all things CONSTANT

[Overboost]

The other thing I forgot to mention although i can't write is as a fact is that. Wastegate duty cycles could be lower for DCI simply because there is an increase in temperature. We know that and increase in temperature for any given fluid in a container or closed environment increases the pressure. Since we target absolute pressure and not air mas this means that the intake that ingests hotter air can essentially hit the boost target at a lower turbine rpm because hotter air is aiding in the pressure increase.

I can add this to the first post if the community agrees.

[PlutoniumTans]

coool

[vasillalov]

^^ Wrong thread maybe?

[PlutoniumTans]

Originally Posted by vasillalov

^^ Wrong thread maybe?

Lmao totally wrong

[Overboost]

Originally Posted by vasillalov

NICE!

Some additional information concerning air and air density:

The colder the air, the higher the density.
The hotter the air, the lower the density.

Air at 30 degrees centigrade (hot summer day) has density of about 1.1644 kg/m3
Air at -20 degrees centigrade (cold winter morning) has density of about 1.3943 kg/m3

So basically this means that there is about 17% difference in air density between a hot summer day and a cold winter morning.

Source: http://en.wikipedia.org/wiki/Air_density

What does that mean:

Well, the molecular "ingredients" of air are the same regardless of the temperature (unless we are talking about extremes here). This means that the ratio between the components of which air is made of is the same: 78% Nitrogen, 21% Oxygen and the rest is just CO2, water vapor and human farts.

When you have denser air, you basically have MORE air in a cubic foot of space. In other words: colder air = more oxygen per unit volume. This means that with colder air, you will have MORE oxygen entering the combustion chamber. This will inevitably be picked up by the O2 sensors which act as snitches for the DME. The DME will detect this higher oxygen condition and will ADD fuel to get to a proper A/F ratio.

More fuel + more oxygen = more Power!

The only reason i stated they vary is because because with increase in kinetic energy equilibrium of molecules almost always shift. Some molecules in air are smaller than others and so we could expect that they will move about more but you are correct in a general regard.

[Overboost]

Originally Posted by Bmwguy11

Actually, the hotter the air, the more the intercooler will cool the air. Intercoolers cool by a percentage, and that is how their efficiency is measured. So air that is 600 degrees going into the intercooler vs 500 degrees into the intercooler, the 600 degree air will have a greater delta in temperature change. This greatly reduces the initial 100 degree difference between the two.

edit: correction, the hotter the air before turbo, the slightly more the turbo compression process will increase that difference. But the intercooler difference is greater.

Intercoolers cool by conduction and convection which change with the environment so there is no way that the percentage efficiency can always be the same. As i said before heat capacity of any form of matter usually changes with temperature. Cooler air providing greater efficiency than hotter air because it has a scientific greater specific latent heat capacity. You are right though. Hotter air does have a greater delta because the heat capacity is lower which means it also loses heat faster but that is not the point of since one can argue that the hotter air will raise the intercooler temperature faster also reducing its efficiency. Intercooler efficiency simply cannot be constant.