Join Date: Nov 2018
Location: Willamette Valley, Oregon, USA
This coming from a commoner with little evidence, the upgrade to a larger FULL LENGTH exhaust can provide some performance enhancement, to a point. Reading around has yielded that a 2&1/4" exhaust is enough for up to about 300 hp (iirc), but supercharging or turbocharging will require 2&1/2" or bigger exhaust.
However, if you only do a muffler addition, there probably won't be much of a performance increase, if at all.