I got a good buddy buying a delta level 3.5 GTR efi rig. He's being sold on stainless works exhaust because it's quieter. Is there any performance gain by going voodoo like delta advertises? Any help would be appreciated. Note he has two children and dealer told him voodoo would not be enjoyable because it's so loud and that the stainless works performs just as well just quieter

They have dyno sheets showing the differences. Look at them and decide if it's worth the potential noise difference. I've heard dealers say all sorts of things that proved to be inaccurate. Some knew better, others just didn't have all the facts and we're being parrots. Some actually know what they're talking about.