The simplest modification requiring next to no skill and with minimal cost is to replace the air filter element with a performance air filter. K&N (from the US) are by far the biggest name in the performance air filter market both worldwide and in the UK, whilst Pipercross (from the UK) are the second largest to them in the UK market. The difference between the two is that the K&N filter element is a cotton gauze material whilst the Pipercross filter element is foam. Both are sprayed with oil to attract and trap dust and the benefit of both is that air flows more easily through them than through a standard paper OE filter, thus releasing up to 2-3bhp.

We also sell cotton gauze filters from Green Filters of France, BMC Filters from Italy (not so well known but presently supplying the Ferrari F1 team) and Jetex Filters from Sweden. All claim different advantages in using their brand, we leave it up to you.....

On the foam filters front we also sell filters from Ramair and ITG. Ramair are presently supplying the Vauxhall team in the BTCC (2004) and ITG have numerous links with F1.

Replacement air filter elements cost £30-£40 whether they are cotton gauze or foam.

An additional benefit of performance filters is that they can be cleaned, re-oiled and used again, so you never have to buy a replacement element again!

Technical Footnote
All air filter manufacturers make statements about their filters producing more air flow etc. but what really happens is that the performance filter produces a smaller pressure drop at a given engine speed than a standard filter. This means the engine sucks in air more efficiently and therefore the engine is more efficient. More efficient = more power.

For fuel injected cars the next step up (and more popular) is to install an induction kit. These require a little more skill but nothing more than a screw driver and small spanner. An induction kit is a cone filter placed as close to the air inlet of the engine as possible. In most cases you remove the original airbox which houses the standard air filter as well as the hoses and any resonator boxes which connected it to the air inlet. The cone filter is then usually attached directly onto the air flow meter which is usually mounted directly onto the inlet manifold. With the removal of all pipework and shortening of the air path, this means that pressure losses are minimised hence power can be increased.

However, the key to good power gains from an induction kit is how much cold air you can get to it. The colder the air then the denser it is and the more dense it is then the more mass of air you are getting into the engine. The ECU then matches the fuel input with this increased mass of air and more power is produced. So the message is : get as much cold air to the cone filter as possible and where necessary put in heat shielding of your own - we sell a range of Thermo Tec products to help with this.

As with replacement filters, there is the same choice of cotton gauze or foam filtering elements. Again the choices are K&N, Green Filters, BMC Filters or Jetex for cotton gauze filters and Pipercross, Ramair or ITG for foam filters. However, there are now also stainless steel mesh filters in the UK market from Quikshift and Powertec. Quikshift have been in the market since 2001 when I met them at the Max Power show and we have supported them ever since (it is their induction kit that I use in my own Impreza). Powertec were launched at the Autosport Show in January 2004 where we were second in the UK to sign up as stock holding dealers. Prices of induction kits of any brand range from approx. £40-£100 and power increases are typically around 4-5 bhp. Some applications such as the Civic Type R are reputed to give 15 bhp!