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Performance air filters has always been a starting point for those who want to take the first step into car tuning. This is because performance air filters are easy to apply and are not so expensive as the other performance tuning components.

I believe the first reason that make all of us purchase a performance air filter is the sporty sound that we all like, but generally there is a belief that performance filters will give you lots of horse power, like a minimum of 5 hp, maybe more, even on a normally aspirated engine.

Now, if I say that performance air filters generate nothing except a sport sound, would you believe it? Your answer would normally be "No !"... Yes, performance air filters do increase horse power but only under certain conditions.. Please continue reading the article..

The theory here is, as you let more air to the combustion chambers to mix with the fuel, you get more power, but the first point is that under which conditions does the air flow and do performance air filters really provide more air as it has been told?

Aerodynamics, or let's call it air flow here, is so complicated so you can never be sure that the replacement of your conventional air filter with an open element filter (like K&N, Kingdragon or Green) will provide more air flow to the intake system

Let's discuss in-box applications like replacing the stock filter with a inbox K&N first, for those who want to apply that kind of air filter mods. On a test which made with a test air box measuring the flow resistance of air yielded the following results:

(The number 100% states the maximum flow resistance to the air, meaning the air is somehow obstructed maximum by the filter or the air box itself while passing through the combustion chambers. Numbers lower than 100 indicate that air flows more easily relatively to the conditions represented with the number 100. It is natural that the air will flow most easily if you detach the filter and the airbox, thus the lower number is 37.5 meaning the least resistance has exposed to the air.

This test has shown that changing the stock filter with an inbox performance filter like K&N is useless unless you make some mods to the airbox, but the most surprising result is that whether it's an original filter or a performance filter like K&N, if you take one of these filters out and apply the test again with an empty air-box, there is still the same resistance like there is a filter inside. That's really really hard to believe, but when you remember the test made with manifold only, you see that air still has a resistance of 37.5. So, that's aerodynamics we talked before which is so hard to understand, and it's not a big surprise that an airbox causes so much resistance.
It's clear that changing the stock filter with an in-box performance filter like K&N is useless unless you make some mods to the airbox, and it's clear that it's not usual to drive without filter and the box, so instead of modifying the box, why don't we use an open element cotton filter? We can get a result between 37.5 (the manifold only) and 56 (modified airbox with K&N). Now, the most vital part of the article.. Please keep up reading..

ormally, the air passing through the intake system is 21% oxygen while nitrous oxide is 33%. We all know that nitrous oxide is a power-boosting, complete and more expensive mod in tuning process, and I hope we all agree on the performance of this mod. Nitro increases the density of the oxygen in the air to 33% from 21%, which is still quite close to the natural density. Do you believe that a cotton performance filter can increase the density of the oxygen? No.. So, the only fact about the open element performance filters is that they only let some more air to pass through, and the most important question is that how much horsepower do we get from them?

Tests on dynamometers show that you will lose horsepower, not gain it if you don't find a way to duct cool air directly to the cone filter. Unshielded cone filters (K&N or any other) were reported to yield a net loss in horse power. The factory filter pulls cool air from outside the engine compartment, while open cone filters will pull warm air from the area behind the radiator. Warm air is less dense than cold, so this can cost between 6-13 HP. Cone filters like K&N and similars only raise the Hp's by 0-2 Hp's on a normally aspirated engine, however, on turbocharged or supercharged engines, the increase is somewhat higher like 8-10 HP, according to the power and vol. of the engine.

Another issue on performance air filters is that they only affect the top end, meaning close to redline. You can feel a power loss at low revs. And one other is that the cotton filters let in considerably more dirt (300-500% more) than stock. Filter allows more dust and fine dirt particles into the engine, but general consensus is that this should make no difference to engine wear.

Filter Maintenance

To maintain good filtration performance, regular cleaning and application of filter oil is necessary. Otherwise the performance will be worse than the original. The cleaning period depends on driving conditions but a 6 month period is acceptable for average maintenance time. Maintenance exist of two sections: Cleaning and oiling.. To clean the filter, pour some gasoline into something like a large, PVC bottle, and dip the filter into the gasoline for 1-2 hours. Rinse the filter and let it dry. Re-oil the filter by spraying the oil onto the inside surface. That's all..


Result

To get HP to increase, you need cold air... hot air will decrease HP. So find a way to isolate the filter. Use a special, large entry box that will help suck the cold air from outside the engine compartment, or cut the hood.
Change your driving characteristics. Change gear at slightly higher revs, cause you will get power at high revs especially closer to redline. (I'm sure you also do that in any case, at least for hearing the sound
Clean and re-oil your filter periodically. Even if you don't clean the filter, just re-oil it so you can be sure that the fine particles or dust can't pass through the filtering element.

To get HP to increase, you need cold air... hot air will decrease HP. So find a way to isolate the filter. Use a special, large entry box that will help suck the cold air from outside the engine compartment, or cut the hood.

Change your driving characteristics. Change gear at slightly higher revs, cause you will get power at high revs especially closer to redline. (I'm sure you also do that in any case, at least for hearing the sound.