An air intake, like a K+N 57i or something... makes the cooper sound awesome. The engine has more growl to it. 
Does give more pep to the performance, but as has been said it is the sound that is so important. It completely changes the way you feel about the car! You perceive it as a sports car and just want to put your foot down all the time. The noise sounds like a movie soundtrack of a car chase movie and is brilliant it suits the cooper totally.salim said:What's an Air intake?. How does it work and why is it so awsome?