with a different air filter? Noise, increased air flow (the stock has more than enough for the stock engine), better dirt filtration?
The stock setup has a cold air intake...after all you are sucking air in from outside the car.
Most filters that advertise "more HP" are inferior to the stock filter in keeping dirt out of the engine..both in terms of size of particles and in terms of amount of particles they let through. I base this statement on a Car and Driver test several years ago as well as some others I've read.
The idea of developing the engine into a more potent performer can be explored better once you define the starting point (what engine you have now...base 2.7 I take it with no mods yet), what performance you are trying to achieve, where you'll use the extra (road, track, AX, etc).
Further thoughts
here
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