Debate continues: K&N filter vs. MPG

[Vwbeamer]

The filter may make more HP,because to measure HP,you have large throttle openings, and airflow becomes important.If the stock filter flows 500cfm and the K&N flows 550,then the motor will make more power.
(assuming it can use the extra CFM.)

For MPG and daily driving, you have small throttle openings and the throttle reduces airflow.

It is likely that the stock filter( which is sized for Wide open throttle) will flow more than enough air without restriction at small throttle upenings. The extra air flow of the k&N is not needed or realized by the engine.

If the engine only needs 100 CFM,it does not matter that the K&N flows 550CFM, it already has more than it needs.

[Christ]

I use a round cone type filter, but it's a stainless steel mesh, like 4 layers thick. I haven't really tested it for airflow or anything, but it sits in the same location as the stock filter did on my Civic, and with the 3" mandrel bent "cold air intake" (eBay special) it seems to be working fine. Oil changes haven't shown any evidence of crap in the engine, and I drive on farm roads with it alot.

The car is sold, but I'm keeping the filter, I'll probably put it on my wife's Grand Prix for now. It's a serviceable filter, that apparently will last "nearly forever". You clean it with warm soapy water, just like your dishes, and there is no oiling necessary. APC makes it. (I know, I know... )

I've personally never seen a gain from K&N filters, and don't plan to speculate on why or why not. I don't care to pay the kind of money that they cost, and then maintaining the filter beyond that, and the vehicle maintenance issues that they're apparently known to cause. I'd rather use a "normal" serviceable filter, like the stainless mesh I have now. IF I ever feel that it's not performing on a particulate filtering level, I'll just add a washable pre-filter to it. (ShopVac FTW!)

To hush the speculative claims that increased airflow through the filter causes better fuel mileage in typical scenarios:

This one is simple, and I can't believe that no one has thought to do it.

If you think your OEM filter is restrictive in normal situations, I want you to set your engine at a specific RPM with the throttle, and have someone watch the tach, or hook up an external tach that you can watch.

Loosen the clamp that holds the air pipe to the filter box, and remove the air pipe from the filter box so that the engine is now "breathing freely". If you notice a change in engine RPM at this point, your OEM filter is creating restriction in your normal driving situations. If no discernible changes are noted in RPM, your air filter is NOT creating restriction in your intake tract.

Another way to test this is to go buy a K&N intake "drop-in" filter. Measure the vacuum at the pre-filter opening in the intake tract, both at idle and at 20% throttle with 0 load using your OEM filter. Use the same procedure to test vacuum at the pre-filter intake opening with the K&N filter installed. The figures at both idle and 20/0 should be either exactly or nearly exactly the same (no more than .5 inHg variance) for both tests.

If they're not, the OEM filter is restrictive during normal driving situations, and the K&N filter may provide some flow benefit for you.

[94blackpathy]

i got mileage gains when i switched from my air intake to a cone and when i changed my exhaust. i went from about 9 mpg to 15 city on average.

[worstmechanic]

But, if the engine control system DOES work as I described, an MAFS that is reading incorrectly shouldn't affect how rich or lean the mixture is. At steady state, the feedback from the O2 sensors should compensate by generating a new fuel/air inlet target, which will, in turn, get everything back to normal.

As far as the test proposed in the previous post, I don't think it will prove anything if the electronic engine control DOES work as I suggested. If you increase the air flow, the MAFS will see it. Since the feedforward control maintains a air/fuel target, the fuel flow will be increased. It will run faster.

Assuming the same engine control system, here's something interesting that should happen. Say you're driving down the road at a steady 60 mph. Your goal is to maintain that 60 mph. Now, let's say I have a genie remove the air filter completely as you're driving. The MAFS sees a higher air flow. The engine control system sees the higher flow, and since it's trying to control the air/fuel ratio at its current target, it increases the fuel flow. (No, you haven't pressed the gas pedal down any more.) As a result of the inrease of air and fuel, your vehicle speeds up. Since your goal is to maintain 60 mph, you lift your foot off the gas pedal a little (which closes the throttle butterfly a little). Air flow decreases, which causes the fuel to decrease. Eventually, you're back at 60 mph, using the same amount of air, and same amount of fuel. The only difference is that you are at a lower throttle position. In other words, the restriction in the air flow has just moved from the air filter to the throttle plate.

[Domman56]

Originally Posted by Formula413

A dirty MAF sensor would cause a lean condition if anything, since more air is entering the engine than the computer is seeing.

haha love the sig man

[Christ]

Originally Posted by worstmechanic

But, if the engine control system DOES work as I described, an MAFS that is reading incorrectly shouldn't affect how rich or lean the mixture is. At steady state, the feedback from the O2 sensors should compensate by generating a new fuel/air inlet target, which will, in turn, get everything back to normal.

As far as the test proposed in the previous post, I don't think it will prove anything if the electronic engine control DOES work as I suggested. If you increase the air flow, the MAFS will see it. Since the feedforward control maintains a air/fuel target, the fuel flow will be increased. It will run faster.

Assuming the same engine control system, here's something interesting that should happen. Say you're driving down the road at a steady 60 mph. Your goal is to maintain that 60 mph. Now, let's say I have a genie remove the air filter completely as you're driving. The MAFS sees a higher air flow. The engine control system sees the higher flow, and since it's trying to control the air/fuel ratio at its current target, it increases the fuel flow. (No, you haven't pressed the gas pedal down any more.) As a result of the inrease of air and fuel, your vehicle speeds up. Since your goal is to maintain 60 mph, you lift your foot off the gas pedal a little (which closes the throttle butterfly a little). Air flow decreases, which causes the fuel to decrease. Eventually, you're back at 60 mph, using the same amount of air, and same amount of fuel. The only difference is that you are at a lower throttle position. In other words, the restriction in the air flow has just moved from the air filter to the throttle plate.

I'm sorry, I think I have to tell you that your nick is accurate at this point.

Under vacuum, higher flow doesn't occur until the engine requires it to. Period.

It doesn't matter if you change the filter, or just remove it altogeher. There is no more flow at 50% throttle with a K&N than there would be at 50% throttle with a paper filter, or no filter at all. That's just how it works.

The largest restriction in an air throttled engine is, and always has been, the throttle plate. As long as whatever blockage is before the throttle plate has less restriction than the throttle plate itself for a given throttle setting, there is no more or less airflow than the engine would have under the same throttle setting with a completely open intake tract.

[alohaspirit]

Originally Posted by 94blackpathy

i got mileage gains when i switched from my air intake to a cone and when i changed my exhaust. i went from about 9 mpg to 15 city on average.

a 6 mpg gain for an air filter and new exhaust?

hmmm



my ranger lost mileage when i switched from a stock airbox to a cone K&N (complete setup)

[Clev]

Originally Posted by alohaspirit

a 6 mpg gain for an air filter and new exhaust?

hmmm

The '94 Pathfinder is rated for 14 mpg city, so maybe a plugged cat or muffler was causing the 9 mpg. My Ranger didn't get any better mileage with the K&N, and actually got worse mileage once the K&N contaminated the MAF. (The fact that the pinging eventually blew the electrode off of a spark plug probably didn't help either.)

[tjts1]

There is no debate. Only the gullible who think a drop in air filter will cure cancer.

[Christ]

That synthetic K&N oil is majick, lemme tell ya. It's like Windex!