I think I've found out why people have FE gains with their CAIs...

[theholycow]

Oh snap, bitten by my own failure to pay attention!

[spotaneagle]

whats really going on here is people are retarded and dont know how to use painters caulk

[GasSavers_Scott]

I can tell you hours of stories from the 80s about figuring how to get a big enough air cleaner under the hood to get a 3% boost and flow and some power. I myself have come up with all sort of combinations of after market air cleaners, dryer hose, and bent up pipes. Sometimes you get some nice intake noise and maybe a boost. With the latest rage of short ramming and long ram cold air intakes, when it comes to dyno numbers, most of the high flow air cleaners come in around 4000 to 5000, but if were trying to keep in the 3000's for MPG, theoretically more flow at low RPM would not boost the static compression ratio much. From published dyno charts, low RPM number are identical. Now fixing a bend in a factory intake tract can smooth out the flow, maybe get rid of some non benefitial turbulence.

The other thing I have come to realize is MICRONS! What is the amount of microns a KnN filter lets through? You cant get free filtering. A friend mechanic I'v known for 10 years at Toyota said that oil/guass filters let more dust microns through. Being that concrete and sand are abrassives, my friend insists that the only thing those filters do is wear out your rings faster. My friend would take a factory V6 air box and adapt it to a 4 cylinder to get more flow, but he says paper is the only way to go.

Is there any data on how much dust gets through on a high flow air filter?

[theholycow]

Originally Posted by Scott

Is there any data on how much dust gets through on a high flow air filter?

There is data around. Here's one low-budget test:
http://bobistheoilguy.com/airfilter/airtest3.htm

I think there are other independent tests. I wouldn't trust any test that could be funded by or connected in any way to any company with a vested interest.

OTOH, as with my observations on oil change habits, I suspect that it's quite rare for a car to go to the junkyard ever having suffered from inadequate filtering.

[Lug_Nut]

Repeated tests over at TDIClub.com have shown that the factory paper air filter (not the STP, Wix, Purolater fitments) actually flows MORE air than the K&N recommended unit.
Remember that the diesels don't have throttle plates that cut down the volume of air per engine stroke, so that may be a difference between the diesel results and those obtained from a throttle plate equipped gasoline fueled engine.
A benefit is that the dry paper filter does not shed oil mist that damages the hot film Mass Air Flow sensor.

More air flow, better filtration, no electronics damage from oil mist.
So I have to replace it, that's a lot cleaner than re-oiling the K&N anyway.

[GasSavers_Willard]

I noticed that the replacement OE filter for my Pilot (green material) had a thin coating of some sort of oil(?). Wonder why the change from dry paper (older Hondas) version to a 'moist' filter?

Either way an OEM air box and clean filter works fine for me.


With my old ITR the AEM cold air sure did make lots of noise at 8,000+ rpm.

[GasSavers_RoadWarrior]

The premium truck/suv filters are oiled now.... it's supposed to stick the dust it won't block, but it's probably to keep them from being blown out...

[Mr. Pig]

I bought a 1997 Z-24 Cavalier/five speed a while back for commuting to work. I averaged 31-32 mpg for the first month of driving. I then decided to do spark plugs, new belt, etc. While working on the car, I went to check the air filter, only to find a mouse nest inside that literally filled the entire air box. and completely covered the filter. I decide to put a cone filter in, so I took the airbox out all together and fitted a cone in it's place. New mpg's were... 31-32 average on my daily commute. If you are driving sensibly to get good mileage, the type of filter and it's state of dirtyness are not all that important unless you are always on the gas in my opinion. Oh yeah, and even with the cone filter directly in the engine compartment, average intake temps were only about 10? F above ambient while moving, they go up when idling of course.

Originally Posted by theholycow

I have a hard time believing that a well developed CAI kit could increase FE for anyone who is driving for FE; though I guess the savings of pumping losses could conceivably help someone who drives anti-FE, if the cold air doesn't bring it down too much (which is possible since factory intakes often get decently cold air anyway).

As for factory paper filters vs. aftermarket, they have every reason and ability to put in one that won't reduce FE. There's plenty of monetary reasons why they should and few why they shouldn't. It's truly hard for me to believe that a manufacturer would be so negligent of their own bottom line for so little reason on a detail that is so popularly scrutinized.

And again, even if it doesn't flow well, it shouldn't affect FE for drivers who care about FE at all.

Don't forget the EPA's own testing on the matter, which showed that even a terribly clogged filter would have little effect on fuel economy:
http://www.fueleconomy.gov/feg/pdfs/...02_26_2009.pdf

[dieselbenz]

My forward facing CAI improved fuel economy especially on the highway. Its a simple setup. Removed the high beam headlight on the driver's side and ran a sealed 3.25" tube from the headlight bucket to the stock airbox. There are no leaks anywhere in the system and all the air is coming in from the front of the car. If i go to neutral at highway speed (over 65mph) the engine will idle at 1000rpm instead of the normal 750rpm. I assume this is because the oncoming air is overpowering the idle control valve. It didn't do this with the stock hot air intake. Either way, this setup was worth about 2mpg on the highway, tested over many many tanks. My all time best highway tank was 39mpg. This is a 1991 bmw 318i. Don't get your panties in the bunch. This isn't the only FE related modification.
So yes REAL forward facing cold air intakes are very effective at improving fuel economy. Autospeed did a great series of articles on forward facing intakes and the clearly quantified the fuel economy benefits. It seems their site is down at the moment but as soon as its up again I'll post the links.

Strainer keeps the larger debris out of the airbox.


Sealed 3.25" tube from the headlight bucket to the airbox.


There is no way for hot air from the engine bay to enter the intake track even at a stop light. The aluminum intake manifold stays at ambient air temperature even when the engine is at operating temperature.


The name of the game is to reduce the pumping losses ahead of the throttle body as much as possible. There is nothing you can do about what happens after the TB. Some people seem to think that pumping losses only happen behind the TB. They are wrong. Feeding the engine the coldest, densest air possible will yield the best fuel economy.

[Brown7]

omg no,

The importance of getting an intake is that it replaces the slinky dryer hoses from the factory. Putting a cotton filter on some crome tube and setting it on top of your still in take air box is not a cai.



a "Ram Air" introduces outside air from either the top or bottem by means of tube. It is still pretty much the stock set up meaning the filter is in the engine compartment.