Induction kits/air filters Standard air filters fitted to most cars are there to serve a purpose, designed cheaply to filter air best as possable but in doing so cause a few problems. Firstly standard paper filters are restrictive meaning your engine has to work to pull air in, put simply it robs your engine of hp(horsepower). Secondly standard air filter boxes have a habbit of being in the right place to soak up heat which makes the air less dense so there is less oxygen in it, less oxygen = less power because oil in the engine needs oxygen to burn. Here are a few facts to bear in mind when buying filters 1.Most aftermarket air filters claim to give increased bhp but most of them dont, they may flow more freely but the gains are over come by the huge increase in charge temps due to silly positioning under the bonnet. 2.Air boxes situated near the front of the car (away form the engine) usually have a 100% cool air feed so a simple pannel filter will do alot more for your bhp than simply removing the airbox and shoving a cone filter on the end! e.g-sierra coswrth touring cars used standard air boxes with pannel fiters for the best results. 3.Cone filters allow you to hear the induction roar created by all engines unlike pannel filters. 4.Foam filters out perform all other filter types in nearly every way. 5.K and N filters are actually one of the worst aftermarket filters due to the fact that the material used gets blocked very quickly and can restict the air flow over foam,mesh etc. And finally the best aftermarket filter kits are sealed airbox type filters that take a 100% cold air intake from the front of the car (lower down the better) such as BMC airfilters and CDA, with the added bonus of having carbon fibre which reflects heat! Its also proven that long length smaller diameter piping from the throttle body to the air filter its self will improve air stability and fast flow giving better torque through the mid range and lower down. Gudie taken from - pocketrockets.uk