Before I start this is all from my personal accounts and are my views and should be taken as so.
Induction Kits - What you need to know
Ok so your looking to improve your cars performance, the easiest way is to improve your cars breathing - This basically means allowing the engine to
draw air in to mix with fuel quicker and then
get it out quicker once its burnt so the process can start again.
Improving you cars induction (air in) can be done with simple to install units.
The Panel Filter
The first is a simple replacement unit that directly replaces your factory air cleaner unit. These are just the same size unit but in a better material than factory items as all cars are built to 1 a budget 2 made to be quiet and 3 be as kind to the enviroment as possible to not mention give a good fuel return.
Most panel filters claim to give a gain but the jury is out on this one, there could be a single bhp or two to be gained here but if truth be know its probally more to do with better filtration and slightly better air flow.
Prices vary due to brand but you could get one between £30-£50 and come in different material like Foam and Cotton depending on brand
The Open Induction Kit
The next is probally the most fimalir, this unit totally replaces the factory air box setup with a open round filter that increases surface area normally because of its design. These units give a advantage due to them being uncovered and open to the under bonnet enviroment there by allowing them to draw as much air in as they like giving a increased induction note. The draws back goes hand in hand with its advantages -
Heat Soak - This where your airfilter draws in warm air from the engine bay and power is lost due to it.
Units can cost as little as £20-£30 for universal or unbranded items which may or maynot have a poorer quality of material (again jury is out on this one). Branded items can cost anywhere between £60 - £100+
Gains have been proven over the years on dynos and can add upto 3bhp or more, dont forget tho a open (any) filter is only as good as its supply of cold air, most branded items you will get a pipe/tube to direct cool air or the kit will use the factory supply that supplied the factory air box
The Shielded Open Induction Kit
With the cons of a open filter some brands supply a heat shield to protect the filter from warm air sources such as manifolds. These can be alittle more expensive than normal items and the jury is out on how good these shield work. Again most will come with a Cold Air Feed to direct cool air into the filter.
Enclosed Filters
The last option is a Enclosed filter which is basically a cone filter in somekind of protective casing. These offer protection from Heat Soak which is a major draw back with the open design. The major draw back with enclosed filters is because they are totally enclosed their only supply of air is through a cold air feed. Unlike a open filter than can directly draw any amount of air it needs but a enclosed filter has draw its supply in from the cold air feed which means that under slow speeds and under hard accelration they can suffer.
This has been backed up on dyno's which cant replicate the onroad situation with air being forced into the system by forward motion of the car.
Gains are hard to agree on as mention cant replicate onroad situations but the theory is sound.
These are generally alot more expensive than a normal or shield open kit with prices starting at £100+ and upwards.
In a Nut Shell
If you want to sum up all of the above it basically fits in to this:
Open = Noise
Enclosed = Performance
There are both pro's and con's for all, budget and application for your car in general are big factors in choosing a filter for you car.
Like i said at the begining this is all my views and should be taken at that.
Hope this was useful