In tuning terms, anything that replaces the standard airbox is considered an induction kit, no matter how simple it is. Here are the basics…
Uprated panel filter and modified stock airboxs
While a direct replacement performance panel filter can sometimes make a small gain when fitted to the standard airbox, the main gains usually come once the airbox is modified to increase flow. Modified airboxes come in various forms – from simply attacking the pre-filter side with a hole saw to allowing air to enter it far easier, to slightly more complex setups creating free flowing cold air feed with larger bore pipework. This is often the cheapest form of induction upgrade, but despite the low cost, can actually be one of the most effective setups on certain cars.
Throwing away the standard airbox and fitting a cone filter is probably the most popular induction mod there is. With the low cost and high availability of universal cone filters – not to mentionthe big difference to under bonnet looks and induction noise – it’s rare to see a modified car without one.
A cone filter is exactly what it says on the tin – an air filter that tends to be shaped like a cone. They are available in a huge variety of sizes, and are almost always used ‘open’ – i.e not enclosed in an airbox, standard or otherwise. They can be fitted almost anywhere, from directly replacing the standard airbox, to using modified pipework to place it elsewhere in the engine bay, or even in the front bumper or scuttle panel.
Cone filters certainly remove any restriction an airbox may give, but they must also be big enough not to be a restriction themselves. The main problem with them is, unlike an airbox – which usually has a cold air feed – there’s usually very little to prevent the air filter sucking in any air it wants, be it hot or cold. So some badly designed cone filter setups won’t gain any power over the standard airbox; in fact if you do it really badly, it could even lose
Cold air induction kits
‘Cold air’ kits come in all shapes and sizes, some with open filters, some enclosed in some form of airbox, but what they all have in common is they attempt to directly feed cold air to the air filter. Some kits actually sit a cone filter outside of the bay (usually in the front bumper or scuttle panel), while others use a small airbox directly fed from tubing originating in the front bumper. Some are simply cone filters within the engine bay, but with heat shielding and pipework attempting to direct cold air towards the filter.
Cold air setups are popular and usually well priced, though care must be taken that the air feed is actually effective – the longer piping involved can potentially create a restriction in itself, leaving you back at performance square one.
In theory at least, a performance airbox is the most effective induction design, allowing both high flow and low air temperatures. But the cost and space required to fit one may not always make them feasible.
As already mentioned, most factory air boxes are designed to silence induction noise and make servicing easy (not to mention being specified with factory power in mind), so creating an airbox that will give better performance than the OE unit is usually possible. The cost of a performance airbox setup is usually much higher than any other induction kit type due to the extra materials and complexity involved. While most race cars have airboxes rather than open cone filters, they often have radically redesigned engine bays to accommodate them.
The main problem with this design comes with big power levels. One you get beyond a certain level of power, even the largest performance airbox that would fit under your bonnet may become a restriction. For this reason, some really high-power road and race cars run open cone filters, or indeed no filter at all, as the increased inlet temps are a
worthwhile trade-off to allow the required airflow to the filter.