K&Ns work v. well. You could use a larger one if you use "pod" or "cone" versions - this would increase the dust capacity. ITG foam filters em to work well in their latest incarnations. Also, there is a French K&N cone filter clone that looks superior to K&N in some cases. I have seen versions with HUGE flared velocity stack ends...K&N is a bit abrupt at the air exit. A K&N pod on an S14 can gain power but you need to buy/make proper heat shielding to lower temps and prevent the ingestion of hot air from the radiator.