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The AMG GT platform — GT, GTS, GTC, GTR, and GTR Pro — uses the M178 4.0-liter twin-turbo V8, a dry-sump variant of the M177 with dedicated turbo hardware and a unique exhaust layout. The factory catalytic converters sit directly downstream of the turbochargers in one of the tightest engine bays in the AMG lineup, creating significant backpressure that limits turbo efficiency and total power output. Replacing them with race downpipes is the single most effective bolt-on modification for any AMG GT variant. This guide covers catless versus 200-cell high-flow cats, real-world power gains by variant, exhaust sound characteristics, fitment...