Originally Posted by Silver on Blacks
I am looking for the turbo spooling noise and I heard you cant get that sound when you have a catted DP. Is this true?
Turbo-spooling noise from a DP is more of a function of the material the DP is made of, and also the method of manufacturer (cast bellmouth vs. "formed" bellmouth). The cast bellmouth (as found on a COBB DP) will be a bit quieter as there is physically more material in the bellmouth area versus a bellmouth that was formed by manipulating the metal to form the bellmouth shape. The process of manipulating the metal to form the bellmouth (think "stretching") results in thinner metal in the bellmouth area which often equals more exhaust noise (& turbo-spooling noise) eminating from the DP area.
COBB has some interesting DP info here:
Make sure to click on the "Click here to view Pictures and more in-depth information" link for more info.