Civic SI (12-15) 3" Header Downpipe

Item # 300383

Unleash the potential of your big displacement K motor with our high flowing 3" Header Downpipe.  This product eliminates BOTH OEM catalytic converters.  Available Catless or with a single High Flow Cat!



  • 3-inch 304 stainless steel piping
  • 3/8" thick flanges
  • Cast stainless steel high flow bellmouth design
  • High quality stainless steel braided flex section with interlock liner
  • Available Catless, or with your choice of High Flow Catalytic Converters
  • Bung for OEM O2 Sensor as well as additional Bung for aftermarket O2 sensor (Plug Provided)
  • Bolts directly to OEM catback exhaust location


Max Horsepower: 206.88 whp (+20.41 whp gain)
Max Torque: 183.74 ft.lbs (+11.24 ft.lbs gain)

Note: Number on Dyno Chat is with Metal HFC and 3" CBE
With Metal Core High Flow Cat ONLY, 13-15 whp gain
With Catless version ONLY, 15-18 whp gain

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