Hey guys there are no performance gains from sti mufflers. They're the same as stock just different tips...some tcp or hi tech quads would give you the same look and 5kw odd on a 3" tbe, just be mindful most aftermarket mufflers drone with a full 3" tbe on an auto... I've been told hi techs don't drone? Haven't tested that myself
they definitely sound better than sti
Also to see the gains from bolt ons you need a re tune, but you dont have to have a retune straight away for things like mufflers, tmic, bov, 'hi flow' panel filter and even a silicon inlet pipe (although don't floor it at the lights with the inlet pipe without a retune - 90% sure it wont do any damage but just in case your ecu cant keep up).
Better to let a good workshop, like msr
, do the inlet pipe as jackson said, but also because they'll run a boost leak test which will save you so much headache later. Seen so many people struggle with boost leak because of DIY pipes
Hopefully this helps and maybe saves some moneys
And if you want to save even more...a good tune can be had for $120 while you're installing all the parts on and once theyre all on - turbo tbe fluffy dice etc...then go to msr for a final tune on the dyno and happy days