Performance Air Filters And Induction Kits

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.

Paper:

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 amounts of air to the engine.

Foam:

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:

Popular Cotton Gauze Air Filter     Cotton Gauze Filter For Carburetor

Cotton gauze filters have been used by some after market companies and even some original applications. These have proved to be popular with both older carbureted engines and modern engines alike due to good filtration and 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 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.

Direct Replacement Performance Filters:

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 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). I had one fitted to a V6 Mondeo a while back and I quite liked the sound. 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.

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 I 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 below for info on hydro-locking).

Honda Civic Si AEM Cold Air InTake

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.

Cold Air Bypass Valve

I 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 I do not know if these can be used on none AEM kits.

Recommendation
I 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, 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, performance air filters still require regular cleaning for optimal performance. Or go for a cold air induction kit with the filtr placed low down by/within the inner wing area and a cold air feed directed through the bumper. 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.

Various Cotton Gauze Performance Air Filters

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 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 properly
2. Some are over priced
3. Some let too much dirt/dust through
4. Some people don’t like the induction roar

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