The TXS downpipe is larger than any other WRX/Sti/FXT downpipe on the market. Why is that important? Because, despite what your girlfriend might tell you, size does matter. Turbochargers work best when there is large pressure and temperature differential across the turbine wheel. Having a large, free flowing downpipe is what give you that large pressure and temperature differential. The downpipe has a 4 inch cast bell mouth which tapers to 3 inch towards the flange end. The downpipe fits all 2002+ WRX, STI, FXT and LGT models although different Catpipes or Racepipes are needed. All TurboXS Exhaust components feature a 5 year warranty! Exhaust components fit both the manual and automatic 2002-04 WRX. *Turbo-back exhaust systems are for off road use only and are not street legal!