Performance Air Filters & Induction Kits

April 10, 2013 By Mike Lee
Last updated on July 27, 2015

Performance Air Filters (Sports Air Filters) – a guide for the asthmatic.

Air Filter Basics

Engines need air, they need to breath, but that air also needs to be filtered, so that debris and dust don’t get into the engine and cause damage, hence the need for an air filter. Basically air filters, filter the air entering the engine.

Common Types Of Air Filters:
There are 3 basic types of material used for air filters. Other materials are used also, such as stainless steel, but we are just concentrating on the more common ones.
Paper Air Filter
Original Panel Filter

Paper air filters are normally flat and pleated (known as a panel filter). They are normally housed in a box and fitted standard by most car manufacturers as they are cost effective. If maintained (cleaned) or replaced regularly they can flow adequate (enough for a mostly standard setup car) amounts of air to the engine.

Foam Filters
Foam Air Filters

Foam filters are normally made from polyurethane wetted with oil. With varying thicknesses they can either have high air flow rates or the thicker ones can be used for high dust filtration.

Cotton Gauze Filter         Cotton Gauze Carb
Popular Cotton Gauze Air Filter      Cotton Gauze Filter For Carburetor

Cotton gauze filters have been used by some aftermarket companies and even some original applications. These have proved to be popular with both older carbureted engines and modern engines alike due to good air flow characteristics. There are oiled (small amount of oil added to protect against dust and water) and dry filters (generally have a sock, that does a similar job). Oiled filters require recharging (cleaning and re-oiling) while the dry socks can just be removed and rinsed in water (please note that excess oil may damage your MAF) – most notably with regards to a hot-film sensor MAF. Many conical cotton gauze filters come with cold air feed ducting, that supposedly delivers cold air (this is only true once you are on the move and cold air is forced/sucked into the ducting). The main problem with the open air filter is the addition of heat getting to them from the engine bay. See below about ducting.

Aftermarket Performance Air Filters

Pioneered by the now famous K&N Company in the 1980’s, aftermarket air filters can improve the cars drivability, throttle response and power (keep reading). However also note that original filters fitted to some cars although by design are restrictive have been found to be more than adequate at supplying good airflow to your standard engine and in some cases better than aftermarket filters. There is always a compromise and some performance air filters will create more or less power at certain engine speeds and temperature changes. Also be aware that there may be an issue with some Mass Air Flow Sensors not being able to cope with the extra debris and oil that some performance filters let through, seek advice.

Direct Replacement Performance Filters:
Cotton Gauze Filter Flat
Cotton Gauze Direct Replacement Filter

A direct replacement performance panel filter can have an airflow that’s a little better than the standard panel filter. The main advantage though is that they can last much longer than the original and can be more effective over time. While the original air filter becomes dirty and restrictive, the performance air filter will still flow very well with the same dirt, due to the way the dirt is trapped.

Cold Air Induction Kits
Cold Air Intake

Cold Air Induction Kit (CAI)

A cold air induction kit replaces the standard air intake box with a conical filter and ducting. Many produce a kind of roar (known as induction roar). In theory they can flow better than the standard air box and filters fitted by the manufacturers due to their design and the materials they are made from, again more airflow can also mean more dirt.

However it’s important to remember that it’s the way the cold air is delivered to the filter that’s important here. Engine bays are hot areas and small increases in the airflow temperature can have a negative effect on power. For this reason we suggest using either a closed unit on a turbocharged car, either a good replacement panel filter or a cold air intake kit, with the filter positioned well away from the engine.

The ducting route is more important than most companies mention. The last thing you want is the ducting to be directed along hot areas of the engine (manifolds etc). It only takes a 10 Degree Celsius increase in air intake to give a 3% loss in power. Also a quick word about under car ducting – not always a good idea, you can still pick up heat from the engine through all those bends you have to make to get it back to the top of the engine (plus those bends cause disruptions to the airflow) and there is always the chance that water may also enter if the car is low and you go through large puddles. It all depends on how much space you have in the engine bay (see ‘Cold Air Bypass Valve’ below for info on hydro-locking and the ‘Recommendation’ section for more ducting advice).

Please see below about high pressure area’s.

Honda Civic Si AEM Cold Air InTake

Ram Air
Ram Air
Pontiac Trans Am, aptly named Ram Air

Briefly, Ram air is the process of placing ducts outside the engine bay, either with side mounted vents, bonnets scoops or from the front of the car. Theoretically, the forward motion of the car forces the air into and along any ducting and into the intake increasing the static air pressure. However it has been shown that below 100mph, it has a limited effect. Also this method requires modifications to the body of your car, as well as increasing the use of your filter as an insect collector. For me the old style roots supercharger on a V8 demonstrates ram air quite well.
Drag Car Scoop

Cold Air Bypass Valve
Cold Air Bypass Valve
We will warn you again that if you allow water into your engine, you will suffer ‘hydrolock’, this is because water cannot be compressed like air, causing damage to the engine. Some manufacturers now have a built in shield, which stops the water from entering the air filter. It’s a case of give with one hand and take with the other. Cold air bypass valves are now available from AEM, they are filtered spacers that contain a valve. Bypass valves fit between 2 connecting intake pipes and will only open when enough vacuum pressure is generated by a blocked filter. Note: These are not intended for use with forced induction and we do not know if these can be used on none AEM kits.

We have several recommendations here (the choice is yours):
We recommend using a cotton gauze filter with a heat shield or something like a Carbon fibre box and feed the cold air into/towards it from either around the headlamp or from the front bumper area or even from the back of the engine bay (anywhere where cold air can be got at or there is a high pressure area that can suck the air in), keeping the ducting as straight as possible (always difficult due to the lack of space in most engine bays). Also consider the size and flow characteristics of the ducting and indeed the whole intake area can benefit from smoothing of any intrusions, as these tend to disrupt the airflow. Oh and don’t forget to clean/oil oiled filters regularly, most performance air filters still require regular cleaning for optimal performance.

OR go for a cold air induction kit with the filter placed low down by/within the inner wing area and a cold air feed directed through the bumper.

OR If you don’t want to spend too much money and can’t be bothered with fitting and ducting (although quite simple) then you can’t go wrong with a direct replacement cotton gauze panel filter placed in the original air box (would recommend this for most applications). If you have no money to spend another option is to improve the airflow into the original box by modifying the ducting into and within the box and remove/cut down your cars resonators (if fitted), these resonators are designed to reduce the noise from induction, but can also reduce the amount of airflow (supposedly), my advice is to research this for your car before attempting this. Also popular amongst those who want a little more noise and airflow for nothing is to drill holes in strategically placed areas in the air box, again do research on your car before attempting this as some filters boxes are badly placed within the engine bay, you do not want hot air from the engine bay (remember, not all mods yield a gain in power and sometimes the opposite can happen when done incorrectly).

Finally: In most cases and certainly if your car is mostly standard, a standard paper filter and airbox have been designed to give adequate amounts of airflow and filtering that may actually be best left alone and indeed the best all-round option.

Boxed Cold Air
Various Cotton Gauze Performance Air Filters

Cold Air Engine Bay
Cotton Gauze Air Filter Located Away
From The Engine And With A Heat Shield

Civic 06 CAI Fujita Intake
Positioned below the wing area and behind the bumper, with probably a cold air feed through the bumper.

Advantages/Disadvantages Of Aftermarket Performance Air Filters

Advantages Of A Performance Air Filter

  1. Easy installation
  2. Generally last longer than the original standard filters
  3. Cost effective in the long run (if you keep the car)
  4. Nice induction roar
  5. Looks nice under the bonnet

Disadvantages Of A Performance Air Filter

  1. Can rob as well as increase horse power if not ducted and protected from the heat properly
  2. Some are over priced
  3. Most will move any power gain further up the rev range
  4. Some let too much dirt/dust through and will require regular cleaning
  5. Some people don’t like the induction roar