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BMW N54 Downpipes: Catless vs. Catted High-Flow Downpipes
N54 Catless vs. Catted Downpipes Why Upgrade my N54 Downpipes? One of the biggest restrictions on the N54 powered 135i, 335i and 535i is the factory catted downpipes. Downpipes bolt directly to the turbochargers and the factory catalytic converters create significant back-pressure which results in slower turbo spool. Modifying your N54 with catless or high-flow catted downpipes