just got that combo, but how often are u supposed to change the filter and how does it sound with the HKS for our sedans.

 

You don't have to change the filter just clean it. I do it twice a year. The Z-tube and pop charger gives a nice sound not sure of the HKS but I know with the stillen cat back it sounds great a wide open throttle IMO.

 

I had the pop charger and z tube on my car for about a couple years before I added the HKS rear section, it sounded pretty mean at wide open throttle. The HKS mostly overpowers the intake as far as sound, it's much louder when you really get on it... I love it.

The main advantage of the pop charger is you *NEVER* have to replace it! You clean it and oil it with filter oil (I've used the K&N kit). I've only done it about once a year over the last 3 years.