My downpipe is 2.5" but then before the cat it goes to 2.25" and stays that size all the way tuntil the Magnaflow muffler which has a 4" tip. I'm changing the muffler because Ive had about 6 or 7 tickets for "Widened Exhaust Outlet" in the last two years, I've decided to go with a Borla Turbo muffler with 2.5" outlet. My 2.25" exhaust worked fine on 9psi but I plan on running higher boost now with my new turbo/built engine ~20 psi.
I'm wondering would an exhaust shop be able to modify my hi-flow cat/resonator that have 2.25" inlets/outlets up to 2.5" inlet/outlet so I could have a 2.5" turbo-back exhaust without having to replace my cat/resonator? Would 3" piping make a big difference in power or only a few little HP? Don't really want to have to get a new downpipe/cat/resonator and a 3" tip would be too large so I'd need it to go down to a 2.5" tip at the muffler anyway...any opinions?

 

Went and got a quote yesterday. They can change the inlets/outlets on my magnaflow cat to 2.5" as well as upgrade all the 2.25" piping to 2.5" and install my new muffler for 250-300. I made an appointment for friday, going to buy a muffler tomorrow I'll post videos of my new exhaust after probably.
If anyone wants a used Magnaflow catback with 2.25" piping/resonator/4"tip muffler I'll sell it for extremely cheap.

 

Hey interested in the exhaust, check your pm's

 

Anyone who has a turbo car and a 2.25" catback, get atleast 2.5" piping right now! Just got my car back and here's what i've noticed
-Deeper Exhaust Tone
-More power throughout RPM range
-Faster Turbo Spool-up

Much better now my downpipe is also 2.5" so I guess its a 2.5" turbo back exhaust with magnaflow hi-flow cat and Magnaflow 5x8 straight through style muffler with 2.5" inlet/outlet.
Very happy with the setup, even without a resonator the exhaust isn't too loud.