Exhaust gasses are guided through 3-inch diameter tubing into the center inlet of the fully-24-inch wide muffler section. Internal to the muffler, the exhaust gasses pass through a reversed Y merge, efficiently splitting the exhaust into separate muffling chambers on each side of the canister. 2.5-inch outlets emerge symmetrically from each side of the canister and direct the exhaust out the rear through quad polished exhaust tips. This straight-through exhaust design is much more effective at reducing exhaust back-pressure as can be seen in the illustrations below: 304 stainless steel is used throughout the exhaust construction. All components are meticulously TIG welded for outstanding appearance and strength. Four custom exhaust tips fill the factory bumper cut-outs perfectly, protruding just enough to show off the COBB logos etched into the top of each polished tip. Perfect fitment is achieved with either the Subaru factory downpipe or the COBB 3" SS Downpipe. The COBB 3" SS Cat-back Exhaust for the 2008+ Subaru STI is a triumph in design and execution. Install the COBB 3" SS Cat-back Exhaust on your STI and experience performance like no other.