high flow air filters like K&N allow u to gain a few BHP
more, and don't really affect your low-end torque. Also, they r
washable so u save on having to throw away used filters and buy new
ones. And since u r not throwing away filters, its more
environmentally friendly too! 
if u want a whole cold air intake, u must be able to install it
such that it is able to draw in cold air. its no point if it is
taking in hot air from the engine bay. U'll probably need to put in
insulation to prevent that from happening. Also, most of your
low-end torque will be lost.
