CAI ?

K&N FIPK 2 is probably the best you can get, there are probably a few others that will disagree. Depending on how modded your vehicle is, you will see anywhere from 5hp up to even 25hp increase. The more modded your vehicle is, the more horsepower you will see..

As for feeling the difference, you will get better throttle response, and your vehicle will progress more smoothly throughout the powerband if I recall correctly.

I am pretty sure MOST setups are CARB approved (aka "smog legal").

Also, that HP range is highly inflated.

With your mods, you MAY see 1hp gain. I guess with certain setups you COULD see some higher gains, but your engine isn't begging to be fed with a lot more air.

Also, by K&N kit, do you just mean a K&N filter OR the actual new ducting? From what I remember about the K&N setups, they are TERRIBLE! They place the filter in the HOT engine bay (do a search for recent CAI posts, you will find link to article about temp differences and effects on HP). If you are going to do something about your air intake, either remove the silencer and get a nice K&N filter OR get a cheap CAI that places the filter in the fenderwell and make sure it has a nice K&N connical filter on it.

Read the article at the link (bottom of post) - cosmetic reasons are about the only reason to add a CAI kit. Removing the stock silencer and adding a K&N flat panel to the stock box works just as well - perhaps because the stock box IS a CAI. No smog-legality issues with the stock box sitting there.

http://www.fordmuscle.com/archives/2002/03/coldair/

If you're looking for bang for the buck while retaining drivability/emissions/fuel mileage - put a set of 3.55's in it, and have tmoss port your lower intake. Those two changes will make a difference you can feel. Without anymore mods than you have, headers (smog legal shorties) won't improve performance - the stock headers won't hinder you til you get up around 280-290 HP.

K&N FIPK is overpriced garbage. CAIs, in general, don't buy you much at all except for looks. Michael is 100% correct. Take the silencer off your stocker and put in a K&N panel filter and spend the savings on something that matters...like beer!