///// How much does air intake temperature matter ?? ////

Andyinchville1

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Hi All,

Been tinkering with the intake on my car to make it freer flowing (for less smoke / better volumetric efficiency) and ideally keep air intake temps down.

I have read that when air intake temps get too high , the computer retards timing (and maybe pulls back fuel?) and that generally hurts performance / economy.

My question is: how many degrees of intake temp is considered "bad" in that regard ?

On the flip side , going whole hog with a big FMIC should keep engine intake temps down BUT putting alot of heat and blocking the AC condenser would cause the AC compressor to work more to provide good AC inside the car and use up engine power to do so ....

Generally speaking, would the FMIC net more positive performance (lower intake temps allowing for optimal timing / fueling etc) OR would the engine having to work harder to work the AC compressor more to make up for the heat in front of the condenser net an overall loss of performance / economy ?

Thanks

Andrew
 

Mongler98

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as far as my understanding on MPG, its moot. BUT if your already at the point of trying to get every % to add up. it does actually make a difference, not so much on power....
the ONLY way your going to get a A2A FMIC to get more results is by spraying water over it or just using a fogging injector pre turbo. Whatever you do its more $ spent on negligible results. IMO...
 

KLXD

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So you've captured waste "heat" from your exhaust by compressing the intake charge. Why do you want to throw some of that energy away by cooling said charge.

Thermodynamically speaking.
 

MukGyver

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I'm no expert but I would think more heat after the turbo increases efficiency not lowers it, because more heat would reduce the amount of fuel required for detonation. But is there a temperature sensor after the turbo in the intake, sending to the ecu? If so I hadn't heard about one. On the other hand cooler air "before" the turbo puts more oxygen through the compressor and we know fires like oxygen! :)
 

Diesl

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I'm not sure what the intercooler has to do with the A/C.
Air density is proportional to 1/absolute temperature, that is air temperature measured in Kelvin. Going from 27C (300K) to 57C (330K) looses 10% of air charge (mass) at the same pressure. Which for the same fuel/air ratio means 10% of power. I'm sure you can figure it out in Fahrenheit.


If you don't care about emissions, then for a diesel you could always just inject more fuel. But hotter air into the cylinders means less air mass, and if you want to keep air to fuel ratio and emissions the same, less power.
 

Mongler98

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All this over how much air you get in an engine that already runs insanely lean all the time.... I have never seen a mpg difference or felt much of a power difference between winter and summer air temps. I'm sure there is a tiny % but.... I've never felt it or been able to measure its difference.
It really does not matter about density because you have a turbo. Less dance, spins faster. More dence air, spins slower to reach the same psi. Psi is just pressure. Pressure is air molecules pushing against stuff. Hotter it is. More psi. Density does not have much to do with it in regards to this be cause density is relative to pressure.
 

Rrusse11

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The whole point of an intercooler is to lower the air temperature after it's been compressed. Mass varies with temp.
Instal a vented fender liner and forget about it. The cost of an FMIC and all the plumbing would never be recovered
with FE improvements, if any. Purely subjective here, but I feel the car boosts better in cold air. People who track IATs,
(intake air temps) reckon it makes a difference keeping temps lower.
 

Mongler98

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lower temps are definitely prefered over hotter ones... the real reason there are upgrades to the cooling of the charged air is for lower EGT's from high boost levels to accommodate more fuel... to lower EGT's....
there are very few things you can spend $ on to recover on MPG in most situations OTHER than driving habit!
 

Andyinchville1

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So you've captured waste "heat" from your exhaust by compressing the intake charge. Why do you want to throw some of that energy away by cooling said charge.

Thermodynamically speaking.
Hi

I understand what you're saying....

I think I've read papers and articles where engines work more efficiently at higher operating temperatures than they are currently run at now ( think vapor carbs and such for old gassers, or turbo and exhaust manifold wraps to help retain heat for better spooling etc...

I think there was even a thread or two here on tdiclub where somebody was modifying thermostats to operate at higher temperatures ( 205 degrees i think) and that seemed to yield higher efficiencies .... maybe not in terms of ultimate high power output but in terms of maximizing power per unit of fuel ( i.e. fuel efficiency).

I agree that higher intake air temperatures would seemingly make sense because the temperature would rise would be faster and not require as much "work" to get it up to combustion temps starting with a higher air intake temperature than with a cold one but maybe there are some curves between oxygen content versus temperature that operate in ways that normally don't seem to make sense? , plus maybe the small difference in air intake temperatures of a an extra hundred degrees or so is not a large enough difference to make a real difference thermodynamically speaking?

I have read that one reason why diesels operate efficiently is because it has relatively high compression ratios compared to gassers and somehow that makes for efficiencies in abd of itself ( I don't remember the exact reason why , just the cause and effect)...

It's the same way a gasoline engine runs more efficiently at higher compression ratios than lower compression ratios up to the point of pre ignition.

I suppose if a custom tune were made to optimize fueling and timing advance using or allowing for higher intake temperatures that may ultimately yield the best results in terms if efficiency but my guess is the reason it doesn't seem to work that way is because the current programming of engines is such that a lot of timing is pulled back with higher temperatures intake wise and that causes more losses in and of itself than any gains that could have resulted from being thermodynamically more efficient by running slightly higher temperatures intake wise and or coolant wise?

It would be interesting if one of the tuners could see and respond to that idea ... i.e. making a tune optimized for higher intake temperatures and engine operating temperatures.
 

Andyinchville1

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I'm not sure what the intercooler has to do with the A/C.
Air density is proportional to 1/absolute temperature, that is air temperature measured in Kelvin. Going from 27C (300K) to 57C (330K) looses 10% of air charge (mass) at the same pressure. Which for the same fuel/air ratio means 10% of power. I'm sure you can figure it out in Fahrenheit.


If you don't care about emissions, then for a diesel you could always just inject more fuel. But hotter air into the cylinders means less air mass, and if you want to keep air to fuel ratio and emissions the same, less power.
Hi

Sorry if my wording wasn't explaining what I was trying to say but maybe an example will ...

Say because a person puts a front-mounted intercooler to reduce air intake temperatures to some optimal temp a person gains 5 horsepower using the same amount of fuel ( presumably because the engine timing wouldn't be retarded because of higher air intake temperatures and is operating more efficiently).

That in itself would be a benefit.

But now suppose that that same front-mounted intercooler is throwing a lot of Heat against the air conditioner condenser and now the engine has to operate the air conditioning compressor more to keep the AC system operating...

if it takes say 10 horsepower to run the ac compressor more that would effectively nullify the benefits received from better efficiency by reduction in air intake temperatures ( the 5 hp gain on this example).

Of course that would only apply when the air conditioning is running or needing to be run which obviously is not year-round necessarily so it's quite possible then the trade-off may be okay overall.

( of course if one wanted maximum benefit for AC and front mount intercooler, maybe the front-mounted intercooler would have to be placed under the Radiator area that way no heat from the intercooler would affect the AC condenser or engine radiator and not having anything behind the fmic with tend to allow or should allow air to flow more freely through the fmic itself ... of course being that much closer to the ground would probably cause or potentially cause more issues onto itself but that was a side thought).
 
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Poor King

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Hi

I understand what you're saying....

I think I've read papers and articles where engines work more efficiently at higher operating temperatures than they are currently run at now ( think vapor carbs and such for old gassers, or turbo and exhaust manifold wraps to help retain heat for better spooling etc...

I think there was even a thread or two here on tdiclub where somebody was modifying thermostats to operate at higher temperatures ( 205 degrees i think) and that seemed to yield higher efficiencies .... maybe not in terms of ultimate high power output but in terms of maximizing power per unit of fuel ( i.e. fuel efficiency).

I agree that higher intake air temperatures would seemingly make sense because the temperature would rise would be faster and not require as much "work" to get it up to combustion temps starting with a higher air intake temperature than with a cold one but maybe there are some curves between oxygen content versus temperature that operate in ways that normally don't seem to make sense? , plus maybe the small difference in air intake temperatures of a an extra hundred degrees or so is not a large enough difference to make a real difference thermodynamically speaking?

I have read that one reason why diesels operate efficiently is because it has relatively high compression ratios compared to gassers and somehow that makes for efficiencies in abd of itself ( I don't remember the exact reason why , just the cause and effect)...

It's the same way a gasoline engine runs more efficiently at higher compression ratios than lower compression ratios up to the point of pre ignition.

I suppose if a custom tune were made to optimize fueling and timing advance using or allowing for higher intake temperatures that may ultimately yield the best results in terms if efficiency but my guess is the reason it doesn't seem to work that way is because the current programming of engines is such that a lot of timing is pulled back with higher temperatures intake wise and that causes more losses in and of itself than any gains that could have resulted from being thermodynamically more efficient by running slightly higher temperatures intake wise and or coolant wise?

It would be interesting if one of the tuners could see and respond to that idea ... i.e. making a tune optimized for higher intake temperatures and engine operating temperatures.

Cold air is more dense therefore packing more water vapor, nitrogen, oxygen, into the combustion chamber than you would with warmer air. Those elements are spread further apart with warm air as the velocity is increased with heat.
 

IndigoBlueWagon

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What Poor King said: colder intake air provides a greater charge to the combustion chamber=more power. I used to run a Scanguage in my Wagon on the track and when IATs got to the 130 range (not difficult when running full out on a warm day), you could feel the ECU dial back boost and timing and reduce power. But it's pretty hard to duplicate that experience on the street. Only thing I've noticed is that the car would sometimes be a bit laggy after idling in traffic on a hot day. I have an upgraded side mount and at the power levels I was making at the time (185 WHP), that seemed to do the job fine. Besides, a bigger intercooler with larger piping means more air to pressurize, meaning more lag.
 

KLXD

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I no one's saying warmer intake temps were good for power. Andy is looking for higher efficiency.

On that subject, for maximum efficiency in a Diesel, you want to run lower compression ratio. As low as possible.

A gas engine is modeled by an Otto cycle and does benefit from high compression. Not so the Diesel cycle.
 

Mongler98

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Unless your smoking black unburn fuel... the more air from colder air is pointless in a diesel that always has an abundance of air in the mix.
 

Andyinchville1

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I no one's saying warmer intake temps were good for power. Andy is looking for higher efficiency.

On that subject, for maximum efficiency in a Diesel, you want to run lower compression ratio. As low as possible.

A gas engine is modeled by an Otto cycle and does benefit from high compression. Not so the Diesel cycle.
Low compression diesel?

I have heard of people who run high boost needing to lower compression to keep head gaskets alive but I cannot say Ive heard of lowering compression otherwise.

How would one benefit from lowering the compression ? how low is too low? ... I have read that worn diesel engines (i.e. low compression) are hard to start (even when warm out!) and may need starting fluid to get started year round :-O
 

KLXD

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The lower the CR in Diesel the higher the efficiency. I assume this is why the TDI has a relatively low CR for a Diesel. Unfortunately it gets harder to start as you said. You can only go as low as is consistent with practical considerations like the available fuel. Leaky rings don't count as lower CR. The CR is still the same but you're loosing air.

Same thing limits the CR in a gas engine, available fuel.

People assume that since higher CR in a gas engine makes it more efficient the same applies to a Diesel. I did and blew a question on a Thermo exam. Answered it without looking into it and got it wrong.

One could ask your question about a gas engine, why would one benefit from higher compression? It's just that we "know it" after years of hearing it but can you explain why"

You have to look a P-V diagram of the Otto cycle. Or maybe it's a T-S. Probably either.
 

JELLOWSUBMARINE

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Diesel is sometimes so counter intuitive. .. Take gasoline principles and flip em' upside down???
 

MukGyver

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The lower the CR in Diesel the higher the efficiency. I assume this is why the TDI has a relatively low CR for a Diesel. Unfortunately it gets harder to start as you said. You can only go as low as is consistent with practical considerations like the available fuel. Leaky rings don't count as lower CR. The CR is still the same but you're loosing air.

Same thing limits the CR in a gas engine, available fuel.

People assume that since higher CR in a gas engine makes it more efficient the same applies to a Diesel. I did and blew a question on a Thermo exam. Answered it without looking into it and got it wrong.

One could ask your question about a gas engine, why would one benefit from higher compression? It's just that we "know it" after years of hearing it but can you explain why"

You have to look a P-V diagram of the Otto cycle. Or maybe it's a T-S. Probably either.
the key to me seems to be naturally aspirated vs not. both turbo'd gassers and TDI's benefit from starting at lower CR. For a gasser 7:0-8:1 CR because the fuel used has a much lower flashpoint.

Inversely the two of them if naturally aspirated gain efficiency (up to a point) from increasing the CR'.

A turbo is just a way of exponentially speeding up the CR (efficiency) in either engine.
 

Curious Chris

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PV=NRT rearranged PV/T = NR Or if you have forgotten or never had chemistry the volume of air is inversely proportional to the temperature. I know with RC2 in my 2002 the stock intercooler heat soaked in under 10 seconds and the fueling dropped way down. I did put in a monster FMIC and that solved the problem,
 

Mongler98

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problem with that is that you don't realize you ALWAYS have an abundance of air hot or cold. air is never the limiting factor unless your blowing coal... but that usually stems from not enough time to fully combust at a certain point... suret here is a tipping point in coal rolling that you are clearly out of air... BUT that is NOT what we are talking about. OP want every single drop of efficiency because he is convinced VW did not do as good as a job as he can with foam insulation on intake pipes and AC driven coolers for intake pipes. LOL
unless your running high egts, or you are rolling coal, you have more than enough air hot or cold to still get 55mpg + its ALL about how you drive.
race application arguments do not apply here.
 

Diesl

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Mongler, that (you always have an abundance of air) is just not true, otherwise you would not need the turbo loader.
 

KLXD

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The OP is after maximum efficiency. Much of this discussion is mixing in maximum power. Not the same thing.

The point of the T/C from an efficiency standpoint is to capture waste heat from the exhaust. For maximum power you do it to allow more fuel to be burned. If you cool the air you can get more in and burn more fuel.
 
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