i dont want to start the same old argument again, but its my opinion so i'll say it again. different induction kits aren't very different to each other, only the price, filtration, and build quality differs, not the performance gains.
a 'better' induction kit will allow air to enter more easily (remove intake restrictions) while maintianing a good level of filtration. any cotton gauze based element will be more than adequate for filtering small particles, while at the same time allowing the element to be cleaned. so a cotton based element is better than a foam (lets dirt in) or paper (blocks and cant be cleaned) element. for that reason keep away from foam or paper based element induction kits and filters.
now the power gains. the air filter will increase the efficiency of the engine by allowing the intake stroke to draw air in more easily. obviously if it is easier to draw air in, it takes less effort, so less power is wasted on the intake. thats where the efficiency increase comes from (more power).
to get a bigger gain, the induction kit needs to make it easier to draw air into the engine. clever students will be thinking "surely having no airfilter is best then?". that is correct, as far as power gains are concerned having no filter will provide the lowest intake restrictions and therefore the biggest gains.
but you need a filter, so which one will provide the lowest intake restrictions and act as if you have no filter? well the truth is it doesn't matter what make or model; what you need to decide is this- what does your engine really need? at what rate will air need to enter the engine?
you can work it out easily. for example a 2.0 engine at 7000rpm will be sucking in (2*7000) 14000litres of air a minute. if thats the redline on your car it won't ever be able to draw air in more quickly than that. if you had a filter that could allow 14 000 litres of air or 1 400 000 litres of air to enter 'unrestricted' per minute there would be no difference as far as the engine is concerned. the gains would be the same, even though one filter is really 100 times better than the other. this is because both filters are good enough for the engine.
so you could have one filter that is 100 times 'better' than another, but if both are good enough for the engine's requirements there is no difference in performance, or power.
now consider the intake restictions of a crappy universal induction kit off ebay that costs £10. they have very low intake restrictions, much lower than the average car needs. my engine can suck more than enough air through the filter virtually 'restriction free'. that means i'm getting the best possible gain from the filter. if i go out and buy a magic BMC filter how can it make a difference, even if it is a lot better, even if it has half the intake restriction, it cant allow my engine to increase its efficiency. the filter is no longer causing any intake restriction so changing it cant make a difference. the throttle body is more likely to be causing intake restrictions now, or even the inlet manifold, or the inlet valves, possibly even the intake pipe connected to the throttle body, but definately not the induciton kit. so no matter which filter i use it wont make a difference.
legally i could sell a BMC filter as 'better' than the ebay universal filter, because (maybe?) it allows air to enter more easily, however if it doesn't increase the efficiency of the engine it wont give better performance, because both filters provide the restriction free air flow required by the engine.
however people who make and sell the more expensive filters will try to convince you that theirs is better for many many reasons (almost as many reasons as why an ecotek valve works
) but the simple fact is that they cost more, and thats all. i've tried more filters on more cars than you would believe (i've even made a few myself), and what do i have on my car? a universal induction kit off ebay that cost less than £10. do you think i'd have one if the other filters gave more power? hell no, but i'm not wasting money on snake oil, i know they wont give me more power, i'm already getting the lowest intake restrictions i need for my engine.
when trying to judge an induciton kit, consider its element surface area and element type. a bigger surface area will mean less intake restriction, a cotton element will filter well and last. then consider what your car needs and be realistic, bigger is better, but only up to the point where the engine is fully satisfied with no intake restriction.
to make it easier to understand, imagine taking a breath. its harder to breathe through a drinking straw, and easiest with your mouth. a wider straw will be easier to breathe through. you can have a bigger and bigger straw making it easier and easier, but once you get to the point where your size lungs can take in the required quantity of air in the required time with no restriciton- then that straw is good enough for your lungs to breathe through and equivalent to your mouth. a bigger straw after that will make no difference, you can still breathe just as easily
that is exactly the same principle and theory as airfilters. so when salesmen try to justify the high cost of their induciton kit just laugh at their lies and keep your wallet in your pocket.
i'm sure plenty of salesmen and their brainwashed customers will happily argue with me, in exactly the same way a bishop and his flock will tell me that jesus loves me, but i still believe in facts, science, mechanics and most of all common sense. if only everyone else would join me.
