Comparing Warm Air Intakes (WAI) & Cold Air Intakes (CAI)

[toomuch]

Comparing Warm Air Intakes (WAI) & Cold Air Intakes (CAI)

My basic point is:
With respect to air intake temperature, maybe there is no difference between a Cold Air Intake and a Warm Air Intake regarding Fuel Economy (FE). Please read on.

CAI:
From what I have gathered, in the performance tuner world, a cold air intake is one of the most basic mods one can do. Power gains can be small, especially for smaller engines. 0.5% improvement is a good minimum starting point for the power gain.
The idea is that air intake is supposed to be placed farther away from the engine than stock, thereby sucking in colder air. The lower the temperature of the air, the denser the air. More air than stock needs more fuel to keep the fuel ratio satisfied. At any given throttle position, this should result in more power than stock since more explosion mixture is being introduced to the explosion chamber.

For the sake of this discussion, let us assume that the only advantage here is the denser (colder) air. (Other advantages of new intake plumbing: less restriction. This may be a result of a more-porous filter, larger intake tube diameter, smoother plumbing, or less bends and turns in the plumbing.)

A cold air intake does not result in a richer mixture of fuel. If a mass ratio of 14.7 to 1, air to fuel, needs to be maintained, then the engine will keep it there. A rich mixture is a mixture with less air (flip side of the coin, more fuel) than the stoich mix requires, and therefore would not be the result of a CAI. (This could be the result of a reprogrammed ECU)

WAI:
A Warm Air Intake is placed closer to the engine than stock to pull in warmer air. The greater the temperature of the air, the less dense the air. Less air than stock needs less fuel to keep the fuel ratio satisfied. At any given throttle position, this should result in less power than stock since less explosion mixture is being introduced to the explosion chamber.

A warm air intake does not result in a leaner mixture of fuel. If a mass ratio of 14.7 to 1, air to fuel, needs to be maintained, then the engine will keep it there. A lean mixture is a mixture with more air (flip side of the coin, less fuel) than the stoich mix requires, and therefore would not be the result of a WAI. (This could be the result of a reprogrammed ECU)

Stoich:
The modern engine is trying to keep a 14.7 to 1 mass ratio of air to fuel.
http://en.wikipedia.org/wiki/Air-fuel_ratio

Hypothetical and demonstrational situation:
So normally, if one is cruising along at 55mph, say the car needs 25 units of power to do this. And to achieve this power the engine needs to run at 2200 rpm.

Now say one has a WAI. Cruising at 2200 rpm, the engine is pulling in less air, and so it is making 24 units of power, and runs at 53 mph. In order to cruise at 55mph, the engine needs to run faster, at 2250 rpms to achieve 25 units of power.

Next, the same vehicle as a CAI. Cruising at 2200 rpm, the engine is pulling in more air, and so it is making 26 units of power, and runs at 57 mph. In order to cruise at 55mph, the engine needs to run slower, at 2150 rpms to achieve 25 units of power.

(assumption about to start)
But all situations should be consuming the same amount of fuel.
(end assumption)

Problem:
I suppose the engine is consuming the same amount of fuel to make the needed power at any rpm?
It seems as if the needed rpm is shifted, but not the fuel consumption?


Point of difference:
The point of difference between CAI, stock, and WAI would be at WOT. At WOT (Wide Open Throttle) the engine should be making the most power (& burning the most fuel) with the CAI, and be making the least amount of power (& burning the least fuel) with the WAI. Maybe this is the only time there is a difference. I would not call it an efficiency, I think it is more of a difference.

Personally, I'll stick with the CAI because when I need the vehicle to go, I need the car to go! And now I realize that with a CAI I am not loosing any MPG when I am trying to be economy minded.


A new direction?:
Maybe eco-modders should be more concerned with gaining the other benefits of a new Air Intake, namely less restriction. This may be a achieved by a more-porous filter, larger intake tube diameter, smoother plumbing, or less bends and turns in the plumbing.
Less restriction should result in better overall breathing efficiencies.
Reprogrammed ECUs for leaner fuel ratios. I do not want to touch this subject any farther than that!

Please Note:
1 I bet I am wrong somewhere. Please, someone put it right!
2 I am just a college student, studying marketing. I have no formal background in any of this. But I do have a hunger for understanding how things work.
3 All of my references are to fuel injected engines with an ECU. I have no knowledge of carburetors.

[tasdrouille]

Originally Posted by toomuch

[...]
Hypothetical and demonstrational situation:
So normally, if one is cruising along at 55mph, say the car needs 25 units of power to do this. And to achieve this power the engine needs to run at 2200 rpm.

That's not really how it works. The 25 units of power for 55 mph can work out, but the 2200 rpm is not to get 25 units of power, but to get 55 mph. For each rpm, there is a certain amount of power available. Actual power will vary depending mostly on the throttle plate openning.

We've already discussed WAIs and CAIs in plenty of threads to great lenghts. You might find the information you are seeking in those threads. If you have any unanswered questions or feel like commenting on some points please do so and it'll be a pleasure to continue the discussion. But I don't think we need to go over this all over again from the beginning.

[toomuch]

Originally Posted by tasdrouille

We've already discussed WAIs and CAIs in plenty of threads to great lenghts. You might find the information you are seeking in those threads. If you have any unanswered questions or feel like commenting on some points please do so and it'll be a pleasure to continue the discussion. But I don't think we need to go over this all over again from the beginning.

OK, sorry about that.

[tjts1]

I think starting this thread was a great idea. This should give everyone that has done cold or warm air intake modification the opportunity to post their before and after results in one place. Maybe we can compile some data.

One point I would add to the original post in this thread. In most modern electronic fuel injected engines the ECU will use the temperature signal from the IAT (intake air temperature) sensor to advance (cold air) or retard (hot air) spark timing in order to prevent detonation. Because of this input to the ECU, any efficiency gained from the low density hot air going into the engine will be lost because of retarded spark timing. The work around this problem would be to manually control the input form the AIT sensor in order to trick the ECU to advance timing. This seems extremely dangerous to me.

[jcantara]

Originally Posted by toomuch

Hypothetical and demonstrational situation:
So normally, if one is cruising along at 55mph, say the car needs 25 units of power to do this. And to achieve this power the engine needs to run at 2200 rpm.

Now say one has a WAI. Cruising at 2200 rpm, the engine is pulling in less air, and so it is making 24 units of power, and runs at 53 mph. In order to cruise at 55mph, the engine needs to run faster, at 2250 rpms to achieve 25 units of power.

Next, the same vehicle as a CAI. Cruising at 2200 rpm, the engine is pulling in more air, and so it is making 26 units of power, and runs at 57 mph. In order to cruise at 55mph, the engine needs to run slower, at 2150 rpms to achieve 25 units of power.

Augh! please don't take this personally, but this couldn't be more wrong. If your wheels are going 55 mph, your engine is turning at only one RPM ever (assuming you are in the same gear, automatic or manual doesn't matter). If you're going 55 mph, your engine will be at say 2200 rpm, whether or not you are flooring it or coasting or whatnot. There is a physical, geared linkage between the wheels and motor, with an exact ratio of # of turns of the engine to # of turns to the wheels. If you measure in your car (in one particular gear) the engine speed at a particular wheel speed, that ratio will always hold up in that gear no matter what. The only single caveat I can think of is an automatic transmission when it's not in lockup mode, but that isn't because of the reasons you list at all.

[Daox]

True, warm air will cause ignition retardation. In some engines this will happen faster than the benefit from the increased load (and reduction of pumping losses). In other engines it will happen slower than the benefit from increased load and you will see benefits from it. It may work great on some engines during the winter, but since ideal intake temps, for example, are around say 80°F the benefit is negated during summer. The point is there are too many variables to have a blanket statement that says they do or don't work.

[tjts1]

Originally Posted by Daox

The point is there are too many variables to have a blanket statement that says they do or don't work.

YES!

[JohnnyGrey]

When I finish my injector driven MPG gauge, I will be happy to do an A/B/A test with the factory cold air intake then with a cone filter right on the throttle body. That will put the whole issue to bed, at least for me. Until then, the Scanguage is not accurate enough to tell if WAIs work. It tells you how much fuel it thinks the engine should get, not what it's actually getting. I notice that after fillups during the time of year with large temperature swings, I have to make significant changes to the fillup trim values.

BTW, jcantara is absolutely right. RPM and MPH are directly related. That's why we call them gear ratios.

[toomuch]

The following is disjunct, but I don't really have a lot of time, but I feel like I owe the replies a post.

You know I was supposed to be working on my thesis (undergrad),which has nothing to do with any kind of engineering or designing, so I had taken a B vitamin complex and some ginkgo biliba. I crapped the starting post out pretty quickly, my apologies.

Tjts1 , it seems like you are not convinced, especially from reading the other posts.

I feel like I opened up a can of worms. I did not realize how many factors go into this equation.

After reading a few threads from a WAI search, I feel like the answer is that there are many factors that affect this situation.
This article surprised me:
http://www.metrompg.com/posts/wai-test.htm

So reduced pumping losses, can someone point me to an explanation of that?
If not I'll keep looking myself.

I will ask my friend, he is the ASE “Master Technician” at the local Firestone. I love this guy, he can smell my car before it hits the parking lot and know how to fix whatever I just broke. Plus he is very nice about answering my 5 technical questions every time I see him.
http://www.ase.com/Template.cfm?Sect...ied_Technician
I am not saying that he is the Dr. Jesus of autoshop, just that he is a pretty good source of info.

How about the other point in my post, improving inefficiency through less intake restriction? Has that a goal of eco-modders new intake systems?

RPMs & Speed & gearing. So even at a cruising load, the power the engine makes does not matter? Maybe as long as it is enough? Thanks for your comments!

[JohnnyGrey]

How about the other point in my post, improving inefficiency through less intake restriction? Has that a goal of eco-modders new intake systems?

Not at all. Well, maybe for the TDI guys, but not for gas engines. Less intake restriction gives you more power at 100% throttle, no less. If you care about MPG, you won't be doing much driving at full throttle. Hell, the reason we have a throttle is to restrict the intake.

[Daox]

Stock intake systems create virtually no restriction at ecodriving rpms. No gains to be had there, sorry.

Pumping losses occur when an engine is not able to take in as much air as it wants to thus creating a vacuum in the intake manifold. For example, lets use a 2 liter engine. Every two times the engine spins around (4 cycle engine) it wants to suck in 2 liters of air. Restrictions occur upstream of the combustion chamber that limit the amount of air that enters the engine. The first item is the intake valve(s). These are controlled by the camshaft and really can't be easily altered. The next item upstread is the throttle. The throttle is used to decrease engine output so you don't accelerate like crazy. However, as you close the throttle, the engine has to work harder as it is still trying to suck in 2 liters of air. This decreases engine efficiency and is why accelerating at high loads is more efficient.

[tasdrouille]

Originally Posted by tjts1

Because of this input to the ECU, any efficiency gained from the low density hot air going into the engine will be lost because of retarded spark timing.

That is assuming a lot. Do you have anything to back this up? AFAIK IAT is not a primary determinant of timing.

The work around this problem would be to manually control the input form the AIT sensor in order to trick the ECU to advance timing. This seems extremely dangerous to me.

That is hardly dangerous unless you floor it, and is a non issue with knock sensor equipped cars.

[Daox]

IAT isn't a primary determinant of timing. However, it will effect timing to some degree. Again, this is going to depend on engine design and tuning.

[tjts1]

Originally Posted by tasdrouille

AFAIK IAT is not a primary determinant of timing.

I never said IAT is "the primary determinant of timing". Please don't try to misinterpret what I said. The ECU sets spark timing based on your RPM, then in addition to that it looks at load and intake air temperature. As the intake air heats up, the ECU retards timing and vice versa.
From my bmw repair manual.


From autospeed.

The resistor trick is based on this idea: you add the resistor to the engine coolant temperature sensor circuit, or the intake air temperature circuit. This tells the ECU that the temperature is different to its actual value, and as a result, the ECU adds more fuel (or less fuel, depending on the direction of the modification), or more ignition timing or less ignition timing (again, depending on which way the mod takes the perceived temperature).

http://autospeed.com/cms/A_110350/article.html

Originally Posted by tasdrouille

That is hardly dangerous unless you floor it, and is a non issue with knock sensor equipped cars.

At low RPM rpm, you don't need to "floor it" in order to reach maximum load and zero vacuum. The throttle body is sized for max load at max RPM. At low rpm you can reach max load at as little as 1/4 throttle. Hook up a vac gauge to your intake manifold and you'll see what I mean.

At this point we have no evident to suggest that a warm air intake will improve fuel economy by reducing the density of the intake air.

[tasdrouille]

AFAIK, the primary determinants of timing are rpm as you said, the coolant temperature, and the fuel quantity to be injected, which is determined by the air mass, which depends on altitude, humidity, ambient temperature, etc.

I never said, nor really thought, that the impact of a WAI on FE was primarily or in minor part due to reduced throttling losses from lesser air density. What I've said in the past though, it that a hot engine is an efficient engine. It's mostly the temperature, not the density.

I'll repost again here the references I've posted a couple times already so people can make up their own minds. It's not me saying it, it's research papers and mechanical engineering textbooks.

- Pre-heated intake mixture at low rotational speed improves combustion. (Chiu and Horng, 1992)
- Specific fuel consumption varies inversely proportional to the square root of the suction air temperature (Nakajima et al. 1969).
- Higher ambient temperature is found to increase the flame speed, the combustion reaction rate, the uniformity of the fuel-air mixture and reduce the heat transfer rate though the cylinder walls (Pulkrabek, 1997).
- For lower temperatures, only a small part of the injected fuel is vaporized, causing nonhomogeneity. As a result, lower flame speeds, higher unburned mixture, higher hydrocarbons and carbon monoxide emissions, and loss of power are observed (Pulkrabek, 1997; Heywood, 1988).

References:
Chiu, C.P., and Horng, R.F., 1992, “Effects of Intake Air Temperature and
Residual Gas Concentration on Cycle-to-Cycle Combustion Variation in a
Two-Stroke Cycle S.I. Engine Equipped with an Air – Assisted Fuel Injection
System”, JSME International Journal, Vol. 37, N.4, pp. 957-965.

Nakajima, K., Shinoda, K., and Onoda, K., 1969, “Experiments on Effects
of Atmospheric Conditions on the Performance of an Automotive Gasoline
Engine”, SAE Transactions, SAE 690166, pp. 745-766.

Pulkrabek, W.W., 1997, “Engineering Fundamentals of the Internal
Combustion Engine”, Prentice Hall, Inc.

Heywood, J.B., 1989, “Internal Combustion Engine Fundamentals”,
McGraw-Hill Book Co.

Finally, I'll post the most useful freely available paper I could find:

Changes of Low Load Engine Parameters by Temperature of Mixture

In this research, they were able to reduce BSFC at low RPM and low load by 7% at 195 F vs 100 F. Also, indicating that density reduced throttling losses have not much to do with it, they measured almost the same throtte position at those two temperatures.

[wizardwizard]

i think this refers to the air pressure in the intake tube while at 1500 rpm @ 25 mph and how this pressure would change immediatly when you hit the gas pedal it starts taking in more air wich means less air would be in the intake area and more air in exaust.
when you press the gas, the pressure changes, the gas is held up by water pressure from the tank as long as you have gas, the air pressure is not as stable as this water pressure so you could have a situation where you cant go any faster cuz you cant get enough air into the intake like if you had a front air dam.
the pressure of the air intake fluctuates in an unstable way as your engine uses more and less of it compared to the flow of the gas which is constant because water (liquid) cannot be compressed or decompressed physically (maybe with chemical reaction)
by using a ram air or cold air, you ensure that the intake air pressure stays up when it is being sucked at varying amounts and changing in a way that is unstable compared to the gas intake pressure which is constant.
it makes it easier for the engine and computer to keep the right fuel air timing ratio if it can control the amount of air and gas it is using with instruments that work 100% of the time.

[Markmysite]

This thread died back in May.... hmmm. It was getting pretty heated ... I would've loved to read more ... lol.

It seems that the debate on this will go on for a long time. Why? Because not all engines are the same. Yes, they function in similar ways, but some cars with MAP sensors will react differently to WAI than those without. The ECM measures the difference between upstream and downstream and calculates mixture based on that in some cars, but not on others. I'm not aware of a comprehensive list that tells you which do and don't either.


Still, I think that most modern cars will not benefit from just putting a WAI on today because the ECU will just readjust because of the sensors. After the O2 sensor is warmed by the exhaust gases it will provide the data for air/fuel ratios.

Ahhhh, but what if you were to use the old foil trick? Carefully wrap the O2 sensor in aluminum foil and use a zip tie to hold it in place (leaving a small path for some air flow)? This would trick the ECU into runner leaner yes?

Well darn, the new O2 sensors don't have that vent hole in back. Rather, they use a wire. Can you limit the flow in a wire? Hmmmm


If you can fix teh O2 sensor issue you've got it solved. You would have the MAP sensors and AIT sensor inline on your WAI they should be taken care of.

Yes, knocking may occur on some cars so you obviously would need to run higher octane gas ... or just forget the whole thing. I think it's worth a try.... especially in the winter.

Who's in?

[tasdrouille]

Well, to sum it up the theory is sound, but ymmv.

I would advise anyone to try it. If the timing is getting pulled back tune for cooler air or get rid of it. If not leave it there.