Do air filters increase car performance?
A K&N panel filter, which I guess is what you are after, will give a very slight improvement on it’s own. Adding an extra cold air feed into you existing filter box along with the K&N filter is a better option. A K&N 57i induction kit will give you a better sound and also slightly better performance, as long as you provide it with a correct cold air feed. The problem with an induction kit, or “cone filter” as they are often known, is that the filter is open to suck in warm air from the engine bay, where as your standard box is completely sealed and can only pull air from outside the engine bay. Another option, although an expensive one, is an aftermarket sealed or closed induction system. Piper-cross make the Viper kit, which retails at well over £100 but BMC make a universal kit which is just as good and is available from Ebay for around £90-100. But be warned, do not expect massive improvements, I know that companies such as K&N will say a kit will give 10% improvement, or +5bhp etc,
I prefer the replacement panels that K&N markets. I was able to beat another car that was identical to the one that I was driving. The only differences were the drivers and I had a K&N panel filter. When I would keep out of the throttle, I got better gas mileage too. Reprograming the ECM and different injectors is not needed. The modern ECM measures air flow and air density. That is why they do not need reprogramming when you move to higher elevations. A drastic change may take a few hundred miles for the ECM to adjust to the change. But it will take very easily to a high air flow filter.
