i was wondering, on my lancer i have 2.25"straight pipe exhauste headers, resonator, and i am trying to decide on my muffler purchase.

my question is on a stright through muffler does it matter if the inlet size is 2.5" or is it better to keep it the same size as the rest of the piping 2.25" (i dont want to lose too much back preasure).

 

Stay with the 2.25", you've already lost some back pressure with all the striaght pipe and header.