98 civic ex sohc vtec.... my question is I got a 4-2-1 dc header and I was wondering if it will help me to change out the stock pipin from the dealership to a 2.5 inch.... I just have a tip on my stock muffler >?? please help

 

yea it would help...if your N/A then i'd go at 2.25 or 2.5 any bigger you'll lose power..