2004-2007 WRX STI Downpipes

The downpipe is the highest-impact exhaust modification you can make to a turbocharged 2004-2007 WRX STI. It replaces the restrictive factory pipe — and on most applications the factory catalytic converter — directly behind the turbo, unlocking the power gains that a tune can then take advantage of. Expect this to be the foundation of any Stage 2 build.

The key choice is catted versus catless. Catted downpipes keep a high-flow catalytic converter: less smell, less smoke, and a much easier time at inspection, at the cost of a few horsepower versus catless. Catless downpipes maximize flow but produce a strong exhaust smell at idle and will not pass emissions testing anywhere it is required. Be honest about your local requirements before choosing.

Construction details matter here because the downpipe lives in the hottest, tightest part of the engine bay. Look for thick-wall stainless steel, a proper flex section or donut gasket to absorb engine movement, and clean welds around the turbo flange. A poor-fitting downpipe causes boost leaks and rattles that are miserable to chase after the fact.

A downpipe requires a tune — running one on the stock calibration risks boost creep and lean conditions. Plan the tune before you buy. Every downpipe in this collection is confirmed for the 2004-2007 WRX STI turbo flange and chassis routing.