K&N air filters

[hattster]

Exactly how much extra BHP would having one of these create??

[len_1]

depends on each individual engine and car... generally they are very good returns for the investment... but only if you're planning on using the car to its full potential. If its for the school run then save your money!!

[Impret-Sir]

On their own, with no other modifications, im afraid they dont produce that much of an increase, maybe 3 or 4 BHP, which you will hardly notice when driving. They are also rather more noisy than the standard filter, unless you mean just the insert to put into your exisiting airbox, these are not so bad on the noise front, but still not going to produce much in the way of a power increase.
If you want to find out how much improvement one would make to your car, try removing your existing filter and driving the car without it, see if you notice an improvement, I doubt you will, and the K&N will be no better.

[erimus1]

Its meant to be the cheapest way of a getting a few extra horses - pund for bhp (on most cars that is) - do bare in mind thought that the main reason for the increase is not actually the filter, but the cold air scoop that is attached too. Higher burn rate with cold air - try putting your foot down in a warm engined car on a cold morning, and then try the same on a warmer afternoon - you'd be surprised at the difference.