bad idea don't do it , all you will be doing is sucking in hot air which is less dense than the cold air the box is getting at the moment , it will make no difference and if any at all it will make your economy and performance worse , the only mod that's worth doing is getting a free'er flowing air filter like pipercross (not k&n or oiled filters as the oil can get on the mass flow sensor causing inaccurate readings or in some cases braking the sensor) but even then free'er flowing filters are only really worth the money when you remap the car as then the engine demands more air