Recently on a trip back home I got 34 mpg which was awesome, at one point with tail wind I averaged 36 mpg. with all my other cars the first thing I always did was rip out the air system and put a cold air tubing and build my own box and put a 9" K&N . I don't want to do that with my Caddy as I like how quiet it is. However, has anyone had experience with putting in a replacement air filter that was either Kool Blue or K&N? What were the gains on the mpgs. Did the volume of the car increase markedly?