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BMW M3 F80 & M4 F82 Downpipe Guide — Catless vs 200-Cell vs 400-Cell GESI, S55 Power Gains, Sound & Installation (2026)
The S55 twin-turbo inline-six responds to downpipes harder than almost any other mod you can bolt on. On the BMW M3 F80 and M4 F82, the factory catalytic converters sit immediately downstream of the twin-scroll turbochargers — creating a restriction right where exhaust gas velocity peaks. Replace them with aftermarket downpipes, pair with a Stage 2 ECU calibration, and you're looking at 500+ WHP from a 3.0-liter six-cylinder. This guide covers everything you need to know before buying downpipes for your F80 M3 or F82/F83 M4: catless versus 200-cell versus 400-cell GESI high-flow cats, real-world dyno numbers, exhaust sound changes,...