For some reason, people seem to think that if they put a "high flow" air filter in their truck, it will get better gas mileage. Well, I don't believe it, and I'm going to explain why.

To start, let's go over the procedure that your engine uses to determine how to use its air. I'm going to use my '97 5.4 for example.

At cruise, the engine uses readings obtained from the barometric pressure sensor, the intake air temp sensor, and the mass airflow sensor to determine (very precisely) how much air is entering the engine at any given moment. It then uses this information to calculate how much fuel to inject into the cylinders to efficiently (and safely) react with the air.

Right?....

My accelerator petal doesn't actually control how much fuel is being pumped into the engine. What it actually controls, is how much AIR it lets through.

So, if I'm at WOT, then the throttle body (via the accelerator petal) is letting Full Flow through. Meaning "it's letting the engine get all the air it can get".

Now, if my accelerator petal is at ANY other position, then the throttle body is LIMITING the ammount of air being ingested by the engine, thereby causing the PCM to limit the ammount of fuel being injected, in an attempt to maintain the proper ratio, resulting in a decrease in power.

Am I right so far?....

So when I'm cruising down the road at a steady 55mph, the throttle body is probably about 90% closed. Letting only enough air into the engine to keep the speed steady. Effectively a huge restriction in the throat of the engine. So tell me.... How is a high flow air filter gonna help me?

Ok, let's assume that my air filter is 50% stopped up. When I go full throttle, there will be a restriction in the airflow. The computer will monitor airflow, and adjust fuel to compensate. So my truck will have less power, than if the air filter was clean.

But if I'm cruising at a steady 55mph, my engine doesn't require full air flow. (remember the throttle body was 90% closed previously) So the 50% stopped up filter won't make a bit of difference. I may have to press the petal further down to make up for the extra restriction, but the computer will still calculate the same air/fuel ratio, and inject the proper ammount of fuel. And get the same gas mileage as before.

So you tell me. How in in the world can a high flow air filter increase fuel mileage in our engines? You already have the biggest restriction possible, (the throttle body). The truth is, it can't. The ONLY thing it can do, is make your gas mileage worse. Because at WOT and really high rpms, your computer will notice a slightly higher airflow, and inject more fuel.

As you can tell by this illustration, no matter what kind of air filter you have, it will only let as much air through as the throttle body will allow.



This is the way I understand our engine's air management procedure. If I'm wrong about anything, please correct me.

 

You have the right idea, but your pedal does control fuel. The tps reads how far the throttle is open and works with the maf sensor and injects the fuel. You will gain maybe 1 mpg with a nice intake system because the engine will not have to work as hard to get air. That is why a turbo/supercharger makes so much power, becaus ethe engine is not working for its air, it is being forced into the engine.

 

Actually i believe forced induction systems make so much more power because they are able to fill the combustion chamber 100% full..

Where as natual air pressure is not enough pressure to compact the cylinders 100%. So each time they are firing they are say only 80% full. Where as a supercharger is forcing and packing that air into the cylinders making them 100% full and allowing for a more powerful explosion. (More Air=more fuel, and More Air+more Fuel= Bigger fire)

This is why when you go to a higher altitude your engine makes less power. At higher elevations there is less Atmospheric pressure to force air into your cylinders. This mabey only making your cylinders say 70% full.

 

Right, but if there was absolutely no restriction in the intake system, there would be a lot more power on a n/a engine. That is why a dirty air filter cost power and gas mileage...

 

No. It controls air. The computer controls fuel.

Power, maybe. But it does not cost gas mileage. At least, not in our engines....

The tps reads how far the throttle is open, but it uses that info to help control the transmission shift points and pressures. It also uses that info to coordinate with the IAC valve. (I think, but not positive on the last part)

The engine works just as hard for the air regardless. Re-read my posts, you're reading too much into the "engine working hard for air" bit...... When the engine is at part throttle, it's because the throttle body is clogging up the intake. (a restriction) So all the "high flowing" attributes of a "high performance" air filter will be negated by the throttle body at cruise. Hence, no mileage increase. It's impossible!!!

An "high flow" air filter can ONLY make fuel mileage worse on our engines. (unless it restricted the intake more than the factory filter)

The only time you can see a horsepower benefit from a high flow filter is at wide open throttle. Because any other time, the throttle body will be a restriction.

Remember ....... More air = more fuel being burned = worse gas mileage

 

Actualy,you are overlooking an important part. Your engine is an air pump. The least amount of restriction and work it has to do drawing air into itself releases more power. That is why a less restrictive filter works. Or anything that improves airflow into the engine. A turbo or sc just forces more air and fuel into the engine to develope more power. A guy i worked with gained mileage by just adding a k&n air filter and tornado inser into his intake tract. The computer does control the amount of air and fuel going into the engine,but the more efficient the engine can work,the less fuel it needs to do its job.

 

exactly... I know for a fact I gained 1mpg with my intake, and my ford taurus was getting 22 on the highway, and with a new filter, i got 25, same driving conditions.

 

Yes that's how it increases wide open power, but it doesn NOT increase gas mileage. The computer doesn't control the ammount of air. It just controls the ammount of fuel to compensate for the ammount of air you give it.

Listen guys, think about this.. You're cruising down the road at 55mph.... The throttle body is mostly closed... If you suddenly removed the air filter, what would happen? The engine would get more air, and the computer would give it more fuel, and the truck would speed up! Then you'd let off the gas a bit (closing the throttle body and thereby increasing it's restriction) and the engine power would decrease back to its normal state....

C'mon fellas, look at my picture.... The object causing all the restriction is the throttle body.... Decrease restriction and the truck will burn more fuel!!

Good for power - Bad for economy.

 

Come to think of it, a forced induction GASOLINE engine will probably get worse fuel economy than a n/a engine. Cause the incoming air will be hotter than normal, and the parasetic drag of the inducer will have no benefiting effects. Because the same throttle body limits air intake. That is, unless that super/turbo charged engine runs a leaner a/f ratio.

 

imagen putting a pretty thick filter mask over your face..

now imagen putting a thinner filter mask over your face

you wont have to breath as hard to get the same amount of air as you would with the thick filter..


same principle for an engine.

oh and wait till tritonpwer gets in here.

 

Imagine a throttle body in your mouth. With it cracked, you just barely can breathe. Open it a little more, and air comes easier.

Now imagine the same throttle body but with an air filter on it. With it cracked, you still barely can breathe, but you might have to open it a smidgen more to get the same ammount of air as before, cause the air filter is restricting it a little too. But you can still get the same ammount just as easily once you open it a little more.

When you open the throttle body completely, however, then your air filter would be keeping you from getting the most you can. So the wide open throttle horsepower may be increased.

But with it cracked, the throttle body is holding you back! Not the air filter.

Yeah, wide open horse power wise, but not gas mileage wise.

 

Air filters can increase mileage. Not that they do in practice, but they can. As has been said, an engine is a pump. Anything you can do to make the pump more efficient, be it a drop in filter, upgrading the exhaust, new intake, etc, it's going to be more efficient.

Now that we have established that, we must also understand that in order for a filter to be of any benefit, it must be creating resistance. Resistance requires energy (fuel/gas and ultimately horse power) to overcome. Eliminating resistance frees up horse power and saves fuel (exactly how aftermarket pulleys help). Resistance has the same affect regardless of throttle levels. Just because resistance exists at WOT does not mean there is none at idle. Even though the throttle body is restricting air flow, thereby holding RPM's down, the engine must still use its own energy to pull air along the intake, and to the throttle body in the first place. The air will not flow through there by its own free will.

Modern day filters are quite large and very efficient in their own right. In order for them to be causing resistance, it must be great enough to be causing a pressure differential. In other words, the engine would have to be "sucking" against the filter. It has to _pull_ air through the filter to combust it. The action of pulling or pumping air through a filter which is causing resistance requires energy. Without resistance, the only energy required from the engine to move the air is the mass of air itself and the friction of that air as it passes through the intake. If the engine is sucking against a filter, and the filter was to be removed out-right, there would be no suction because the filter would no longer be causing resistance. This is the way all induction parts must be measured to establish a benefit. You can install the baddest *** intake in the world, if their is no pressure differential in the factory intake, no resistance, the new intake will not be helping power or economy.

If you take two pressure (barometric) sensors, insert one behind the filter, and one in open air to measure ambient pressure, and run the engine through its normal operation conditions, if you detect pressure lower than ambient behind the filter, the filter is causing resistance. Now, there will always be _some_ difference in pressure, if there wasn't any, no air would be moving through it because air will only move from areas of high pressure to lower pressure. The question is simply this.... Is there enough difference in pressure there to attribute to the filter causing resistance to air flow? If there is, the filter should be replaced with one that has less resistance. Doing so will increase efficiency and economy.

It's that simple.

 

thanks tritonpwr and you can talk about my mom all you want.

 

Not you too!

Ok here goes again....

Let's say you have 3 baro sensors... One on the outside, one after the air filter, and one after the throttle body.

At wide open throttle, the baro on the outside will read the highest, and the one inside the air filter will be slightly lower, and the same as the one after the throttle body. (nearly the same anyway, cause the tb vane causes some resistance....)

Let's say that it takes 30% power to maintain 55mph.


Ok, at 30% power, the baro on the outside will read the highest, the one behind the filter will read slightly lower, and the one after the throttle body will be VERY low, cause the throttle body is closed a lot.

Let's say we take the air filter off....

At 30% power, the baro on the outside will be the same as on the inside, but the baro after the throttle body will be at the exact same LOW level as it was in the previous example.

See, In order to maintain 30% power, the throttle body had to close to make up for the increased baro pressure inside the tube, caused by a lack of filter. If you had not closed the throttle body, then the pcm would have sent more fuel to mix with the extra air, and you would be OVER 30% power.

Ya'll are thinking about this from a free breathing (diesel) perspective. Our engines are controlled by choking them. Not by regulating fuel. The fuel is a constant that is directly porportional to air VOLUME.

The throttle body is the choker. The air filter adds a little choking to the process. If you remove the air filter, the throttle body just has to make up for it by choking the engine more! Else, the engine would get more air, (and more fuel) and speed up. (eg. 32% power)

But we're maintaining 30% power, remember? Cause at 32% power, the engine is burning more fuel, and we're speeding up.

Simple once you get past the "engine working harder for air"

The air filter only holds you back from max power once the throttle body restriction is removed. (eg full throttle)

Anytime you decrease restriction, you burn more fuel. It's as simple as that.

They can increase wide open horse power only. But they CANNOT increase fuel mileage at all. NONE! Impossible! Will not happen.

I think ya'll are attributing throttle position with fuel, but it doesn't work like that. You can smash your intake tube 3/4 shut, and floor it, and it will still mix the right ammount of fuel with the right ammount of air. You won't have as much power, but you will get the same fuel mileage.

(actually, your engine knows when you go WOT and it enriches the mixture and retards the timing, so my above example isn't exactly true..)

 

What you are thinking is that except for WOT, whatever is before the TB doesn't make any difference, and that's absolutley wrong regardless of what logic you try to use to reinforce your opinion.


Read this part again...


Resistance has the same affect regardless of throttle levels. Just because resistance exists at WOT does not mean there is none at idle. Even though the throttle body is restricting air flow, thereby holding RPM's down, the engine must still use its own energy to pull air along the intake, and to the throttle body in the first place. The air will not flow through there by its own free will.