i got a tl type s... im thinking of keeping the 2.25 inch exhaust piping and putting hks hi power mufflers... would this mod get me more hp then just buying a after market cat back exhaust that has 2.5 inch piping

 

the catback would yield better gains because it's a better flowing system

 

but isnt it better to keep more back pressure

 

Yes, somewhat, for low end torque, but no for top end HP