I like to run on the street with 12 disks. I feel this gives me a little more than stock back pressure. The idea being more low end torque - quicker off the line. On the track I take off all the disks and end cap to produce less back pressure. Less back pressure means more high end HP. The sound with the all of the disks off is awsome but really to loud for everyday street use. With the disks on it is def. louder than stock but not annoyingly loud. Once the Trapps break in the burble burble sound is great. I get compliments from people all the time about the sound of the car..