The Forester XT Exhaust uses our 3 inch from the front flange all the way to our Staight through design muffler with a 3.5 inch tip. This is hands the the best sounding exhaust for the Forester XT and to top it all off it doesnt reduce down to 2.5 inches anywhere unlike some of the other exhaust systems. You should see a 10-12 whp gain with this catback without a problem.