This is the same exhaust system I have on my car. I have not heard anything louder than this except for the noweed cutouts but there not running through the mufflers. It sounds awesome inside and outside the car. Its not too loud in the car and there is no drone either. If you are going to modify the motor i.e. cam, nitrous, ect. then go with the 2" primary tube headers otherwise 1 7/8" will be fine. I have hi-flow cats on mine to stay legal. There is no power gain not running cats its just a little louder without them. The quality and craftmenship of Stainless Works is second to none and because they make the whole system from the headers to the polished tips it bolts up without any problems. Hope this helps.
http://www.stainlessworks.net/cart/index.php
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Hennessy CAI w/heat shield, Stainless Works 2" long tube headers, hi-flow cats, full 3" exhaust with aggressive s-tube mufflers.