[lineslinger]

It is my understanding that the spiral inserts were meant to be used as a "volume" control while minimizing flow restriction, and that when they were removed (making things a lot louder) you could regain the lost hp for your immediate wants/needs say for track runs etc.
Are you talking about a sidepipe setup with reasonable DB output while still retaining optimal HP? I have always read that it is pretty much of a compromise, flow restriction equals a loss of HP and the best most can do is find a balance between restriction/volume as opposed to running open pipes which in many places will get you pulled over, ticketed, complaints from neighbors, accelerated hearing loss etc.
If there is an alteranative that won't get you arrested I would love to hear about it.