Do Cold Air Intakes Really Work?

[LEM]

Would a CAI help with gas mileage and power on a 2008 4Runner V8? Which "brand" is best? What are your experiences with them?

Thanks.

[Alan Cohen]

Cold air intakes do work , they do this by allowing the engine to breath better. But there is a down fall to allowing more air into the motor. The filters medium used in the cold air intakes do not filter the air as well as the original paper filters.
Another thing you can do is put a free flowing exhaust system in to complement the cold air intake. Doing this will help the engine breath even better.
I would recommend having someone reflash the engine control computer so the changes can take effect. Without a reflash of clearing of the engine control computer, it will take a long time for the changes to take effect.
Using a good synthetic motor oil like MOTUL 5100 T4 will cut down on the internal friction of your engine improving the mileage. I use it in my car and I've noticed a 5% increase in fuel mileage.
For more information like this and to find high quality, honest shops to do the installation, go to [link removed by moderator].

[fourwd1]

The idea behind a CAI is to get colder outside air to the intake, as colder air is more dense (so more oxygen to burn). Since more air requires more fuel, the result should be more power. But more fuel usually means less MPG, if you are taking advantage of the increase in power.

But almost every vehicle already gets intake air delivered form outside the engine compartment (in the olden days the air cleaner took the air from inside the engine compartment, so it was warm and less dense).

So does a CAI really make a big difference? it's really hard to say without having a dyno available for before and after testing.

[Alan Cohen]

I agree that the CAI is made to get colder dense air into the engine which is more oxygen rich. But any motor which breathes better can produce more power. By producing more power, less throttle is needed to bring it up to speed. In this process, a educated driver can use less throttle to produce the same power the engine had before the CAI was installed thus using less fuel to do the job. It's all in the way you drive the vehicle. Any vehicle can be driven in a way to get better fuel mileage. But is that what you want to do?

[fourwd1]

Originally Posted by Alan Cohen

... By producing more power, less throttle is needed to bring it up to speed. In this process, a educated driver can use less throttle to produce the same power the engine had before the CAI was installed thus using less fuel to do the job...

And there's the problem.

As I said, most people take advantage of the new found power, using more fuel and lowering their MPG.

[Brian R.]

I don't agree with these supposed benefits of a CAI. If you can intake more air or colder air (same thing) then you will be able to make more horsepower at WOT. That's a given by the nature of the beast. The more air and fuel you consume, the more horsepower you generate.

The part I don't buy into is any increase in gas mileage which is the whole deal for 99% of the time driving. No matter how much air or how cold the air, the limiting factor in your intake is the throttle plate. If you want to drive 50 mph, then you adjust your throttle opening to give you that. You need a specific amount of gas to drive your vehicle at 50 mph and it is independent of the air intake properties. It only depends on how much air your throttle lets in - therefore, how much gas is metered by the ECM. No matter how much air is available from some intake, your throttle is what limits what gets in to your engine. If the air is colder, you will just have a smaller throttle opening, but the amount of oxygen will still be the same, and so will the amount of gas injected to burn that oxygen. So, no matter what intake you have, you will still burn the same amount of fuel per mile to keep your engine at 50 mph.

The only way you can increase your gas mileage with a computer controlling your vehicle's gas injection is by changing your driving habits or increasing the inherent efficiency of the engine by decreasing friction, changing gear ratios etc. Increasing horsepower at WOT is a whole different ballgame and not related to fuel economy.

JMHO

[Alan Cohen]

A cold air intake not only lets more air into the intake, the air is more dense. When air is colder, the oxygen content is richer. Given that, if the air going by the throttle place is more oxygen rich, the fuel will be burned more efficiently.When an engine runs more efficiently, it uses less fuel to create the same amount of power. I have proven this myself with many vehicles that I have owned and modified myself.

[Brian R.]

Originally Posted by Alan Cohen

A cold air intake not only lets more air into the intake, the air is more dense. When air is colder, the oxygen content is richer. Given that, if the air going by the throttle place is more oxygen rich, the fuel will be burned more efficiently.When an engine runs more efficiently, it uses less fuel to create the same amount of power. I have proven this myself with many vehicles that I have owned and modified myself.

The oxygen content of the intake air has no effect on the efficiency of the engine or the burning of fuel under normal driving conditions. The ECM meters fuel based upon the oxygen content and gives no more or no less than is needed. If you are sucking in denser air, you will have to back off on the throttle to keep your car at some particular speed, decreasing the oxygen content per rpm to where it was before. Do not confuse power with efficiency. Under WOT, there is a significant difference in performance with a less restrictive intake.

Perhaps you are relating your experience with carbuerated engines which have a whole different set of operating characteristics.

[Alan Cohen]

The ECM does not measure the oxygen content of the air coming into the the engine. It measures the mass of the air coming in. It does this by sending a constant voltage across a wire in the air mass sensor, holding it at a constant temp. The more air coming into the motor (air volume) the greater the air mass, the higher the voltage has to be to keep the sensor at a constant voltage. The ECM measures the voltage using this measurement for the air mass.
The oxygen sensor measures the oxygen content of the exhaust to measure how efficiently the fuel is being burned. The ECM tries to keep the fuel mixture at approx
14.6/1 air it fuel ratio.
So if the engine is getting more cold dense air (more oxygen rich) the fuel will burn more efficiently having the ECM lean the mixture out, using less fuel.
The throttle body only changes the volume of air coming into the engine, not the oxygen content.
Check out more informative articles like this at
http://www.laautoreferral.com

[Brian R.]

Originally Posted by Alan Cohen

The ECM does not measure the oxygen content of the air coming into the the engine. It measures the mass of the air coming in. It does this by sending a constant voltage across a wire in the air mass sensor, holding it at a constant temp. The more air coming into the motor (air volume) the greater the air mass, the higher the voltage has to be to keep the sensor at a constant voltage. The ECM measures the voltage using this measurement for the air mass.
The oxygen sensor measures the oxygen content of the exhaust to measure how efficiently the fuel is being burned. The ECM tries to keep the fuel mixture at approx
14.6/1 air it fuel ratio.
So if the engine is getting more cold dense air (more oxygen rich) the fuel will burn more efficiently having the ECM lean the mixture out, using less fuel.
The throttle body only changes the volume of air coming into the engine, not the oxygen content.
Check out more informative articles like this at
http://www.laautoreferral.com

The ECM meters fuel based on the measured oxygen content in the burned gases in the exhaust (HO2 or A/F Ratio sensors), not the intake. Not all engines even measure the air or oxygen in the intake (for example the 5S-FE). Your entire logic is based on a bad assumption.

[LEM]

Great discussion and debate.

Let me see if I understand this.

Colder air is denser, thus having greater oxygen mass per volume. A MAF sensor essentially measuers the volumetric flow of the air. The throttle plate adjusts to control volumetric flow of air, so at the same volume flowrate, colder air will provide more oxygen to the combustion chamber than warmer air. Right?

Okay, the optimum air-to-fuel MASS ratio is 14.64:1. The ECM tries to maintain this ratio by adjusting the throttle plate opening as the flow of fuel is increased by the accelerator.

It seems to me that by increasing the oxygen content of the air, the combustion will be more efficient, more quickly expanding the volume of the air-fuel mixture in the cylinder, creating more pressure to drive the piston, and thus producing more horsepower. Right?

So we should get more power for the same fuel mass with the colder, denser air. Right?

For the sake of this exercise, let's say that vehicle speed is directly proportional to horsepower, laying aside frictional losses due to mechanical linkages, the tires, the wind, etc.

Consider two identical vehicles, one with an CAI and one with the stock air filter. Assuming both vehicles require the exact same horsepower to maintain 60 mph, it would seem that the vehicle with the CAI would create that horsepower with less fuel because its combustion is more effcient. If this is correct, then a CAI would increase power and gas mileage, assuming the driving habits are consistent.

Is my logic sound?

Thanks.

[Alan Cohen]

LEM, you are correct in all of your assumptions. There is only one thing I would like to change in what you said. The ECM doesn't adjust the throttle opening to keep the air/fuel ratio at the 14.6/1 level, it adds or subtracts to the amount of time in miliseconds that the injectors are opened. Everything else you stated is correct and is exactly the point I was trying to make.

[Brian R.]

Originally Posted by LEM

Great discussion and debate.

Let me see if I understand this.

Colder air is denser, thus having greater oxygen mass per volume. A MAF sensor essentially measuers the volumetric flow of the air. The throttle plate adjusts to control volumetric flow of air, so at the same volume flowrate, colder air will provide more oxygen to the combustion chamber than warmer air. Right?

No, this is only the argument made by Alan Cohen which is incorrect.
What he is saying is only true if you are in open-loop mode of fuel metering (cold engine, wide open throttle or closed throttle). Then, the ECM meters fuel based on intake and engine parameters. Some engines don't montor intake air volume or mass at all.

In closed-loop mode (normal running conditions - engine at normal operating temperature and hot oxygen or A/F Ratio sensor, and relatively constant speed), the ECM monitors the oxygen content of the exhaust gases and meters more or less fuel based on that, not on the oxygen content or temperature of the intake air.

See the following technical articles:
http://www.autoshop101.com/forms/h37.pdf
http://www.autoshop101.com/forms/h44.pdf
http://www.autoshop101.com/forms/h55.pdf
http://www.autoshop101.com/forms/h58.pdf

Originally Posted by LEM

Okay, the optimum air-to-fuel MASS ratio is 14.64:1. The ECM tries to maintain this ratio by adjusting the throttle plate opening as the flow of fuel is increased by the accelerator.

It seems to me that by increasing the oxygen content of the air, the combustion will be more efficient, more quickly expanding the volume of the air-fuel mixture in the cylinder, creating more pressure to drive the piston, and thus producing more horsepower. Right?

You have to compare the mileage you get from your car at any constant speed. Then everything is constant except your engine efficiency. It is the only way to compare mileage without bringing into play other variables like wind resistance, rolling resistance, engine rpm, etc.

The answer to your question is no, combustion will not be more efficient with greater oxygen content. The greater oxygen content will just give you more power since the ECM will meter more fuel. The added power will cause your speed to increase at some constant throttle opening.

To maintain constant speed down the road, which is how we have to compare mileage before and after a change in intake air density, you must decrease the throttle opening to keep your speed constant because of the greater engine power resulting from the increased oxygen content. On the other hand, if you keep your throttle opening constant, the greater oxygen content will be measured by the ECM in the exhaust and will cause it to meter more fuel, increasing your power and causing you to speed up unless you decrease the throttle opening. Since the power you generate is proportional to the fuel burned, not the oxygen content, to maintain a constant speed after you allow denser air in your engine, you will have to reduce the throttle opening, allowing less of the higher-density air into the engine and thus burning less fuel to maintain a constant speed.

The end result is that you will burn the same amount of fuel (same fuel economy) to maintain a constant speed with higher density air because you will be forced to close the throttle plate (letting less of the air into the intake manifold) to maintain the constant speed. The confusion in Alan Cohen's logic is that he thinks the fuel is metered by the air through the intake as measured by a air meter, when in reality it is metered by the air allowed by your gas pedal through the throttle plate and measured in the exhaust. Any increase in power owing to a cold-air intake is translated into a decrease throttle opening or a higher HP at any constant throttle setting. If you are varying the density of the air, you can keep the throttle opening constant or the vehicle speed constant, but you cannot do both.

Originally Posted by LEM

So we should get more power for the same fuel mass with the colder, denser air. Right?

No, the power is only determined by the amount of fuel, not the amount of air. When you are running at a normal fuel/air ratio, if you keep the fuel quantity constant and let in more or colder air, you will run lean. Burning lean is not what you want for optimum power.

Originally Posted by LEM

For the sake of this exercise, let's say that vehicle speed is directly proportional to horsepower, laying aside frictional losses due to mechanical linkages, the tires, the wind, etc.

Consider two identical vehicles, one with an CAI and one with the stock air filter. Assuming both vehicles require the exact same horsepower to maintain 60 mph, it would seem that the vehicle with the CAI would create that horsepower with less fuel because its combustion is more efficient. If this is correct, then a CAI would increase power and gas mileage, assuming the driving habits are consistent.

Is my logic sound?

No, the power is determined by the amount of fuel burned. Less fuel will create less power. The vehicle with the CAI will burn more fuel at any constant throttle opening and the same fuel at any constant vehicle speed. The CAI does not increase the efficiency of the combustion.

The key facts to understanding this issue are the following:

1. The power of an engine is only determined by how much gas it burns, assuming it has sufficient oxygen.

2. Oxygen is necessary for combustion, but does not add to power above the ideal fuel/oxygen ratio.

3. Fuel is metered by the ECM based on the oxygen content of the exhaust gases, not what is in the intake air.

4. If you have too little or too much fuel metered, then it shows up in the exhaust as too much or too little oxygen, respectively, and

5. The oxygen content is measured by the oxygen or Air/Fuel Ratio sensor. This is the definition of closed-loop feedback.

6. If the oxygen sensor signals that there is too much oxygen in the exhaust gases, the ECM meters more fuel. The ECM cuts back on metered fuel when the oxygen sensor says there is a low oxygen content.

7. Engine power and thus car speed is controlled by the throttle plate opening which in turn is changed by the gas pedal position. You adjust your car speed by opening the throttle to allow a certain amount of oxygen to get into your engine which in turn determines the fuel metered by the ECM through the injectors.

8. Engines with carburetors do not follow the above logic.

[Alan Cohen]

If adding colder denser air to an internal combustion increases power, and by increasing power means less throttle opening to create the same amount of power, doesn't that mean that less fuel is going to be used because the Mass Air Flow sensor will measure less air flow causing the ECM to inject less gas?
See what others have to say about this:
http://www.bestcoldairintakes.com/20...crease-MPG.htm
Here's another: http://www.bestcoldairintakes.com/20...crease-MPG.htm
Another: http://www.bestcoldairintakes.com/20...ave-On-Gas.htm

It seems that I'm not the only one saying that cold air intakes improve fuel mileage.

[Brian R.]

Originally Posted by Alan Cohen

If adding colder denser air to an internal combustion increases power, and by increasing power means less throttle opening to create the same amount of power, doesn't that mean that less fuel is going to be used because the Mass Air Flow sensor will measure less air flow causing the ECM to inject less gas?

No. First of all, and to repeat myself for the third time, the MAF meter does not provide data to the ECM for metering fuel under normal operating conditions (closed-loop operation). Not all modern engines even use a MAF meter or a method of measuring air flow in the intake. Read the technical articles I provided in the above post.

The fuel metering is determined by the ECM using data from oxygen sensor in the exhaust. It is called an oxygen sensor because it measures the oxygen content of the exhaust gases and tells the ECM to add fuel. When you increase the intake air density, you must decrease the throttle opening to compensate for the increased air density. The result of this is the same amount of fuel will be used to maintain a certain speed. The fuel burned determines the power of the engine and thus the speed. With a CAI, you will consume more gas and, as a consequence, be forced to cut back on the throttle to maintain a certain speed. The net effect of cutting back on the throttle will be to use less gas, but it will be the same amount of gas as you used previously without the CAI. The quantity of gas burned determines the power (speed) of your engine. Unless you change the geometry of the combustion chamber, you will not get additional efficiency from any particular well-maintained engine.

As far as others supporting your argument, there are no limits to how many wrong opinions there are in the world. Doesn't it seem strange to you that with gas mileage being so important, car makers are not just jumping all over themselves to put in these intakes which supposedly support higher gas mileage? It is all hype and imagination on your and other's part. Provide us with an actual published mileage investigation by Consumer Union or other unbiased agency and I will be the first to admit I was wrong. Data from someone who just burned their hard-earned cash on a CAI or data from a manufacturer or distributor is nothing more than wishful thinking, bad data, or simply imaginative marketing - and false marketing at that.

Here is a quote from your reference:
"I've learned that adding a cold air intake to a car's engine will increase the miles per gallon anywhere from three to seven or eight miles per gallon, depending on what kind of engine your car has, your own driving habits, the elevation you live at, and other factors. "

This is simply an opinion from someone who either has never tested a CAI under reasonable conditions, or is providing blatently false information because they sell or market them. You don't usually get this much gas mileage going from a 6 cylinder to a 4 cylinder, a whole different engine - and you expect me to believe that this will result simply from putting slightly cooler air into the engine intake with the ECM compensating for this increase in air density?

If you don't read and understand the content of the technical articles I have linked to in the above post, you cannot discuss this issue. You are simply basing your opinions on incorrect fuel metering assumptions and therefore your entire discussion on a false premise.