zero gain. your stock 2.75" piping is already pretty much too big for your GT. The GT500 uses the same 2.75" piping your car already has. You'll need around 500hp to even consider the need to go bigger than 2.5", and 2.75" would need north of 650hp. 3" would be good until over 800hp. you're at half of that roughly. it's overkill. Even at those numbers (650rwhp for 2.75" you aren't leaving much on the table not going bigger. you could in theory go down to 2.5" piping and have enough to support your GT.
Last edited by TheDivaDanielle; 08-25-2014 at 05:42 PM.