BMW Moves to a Single Twin-Scroll Turbo for Efficiency
BMW shifted from its older non-sequential Twin Turbo setup on the 3.0-liter inline-sixes to a single twin-scroll turbo (the N55) to cut fuel consumption and emissions, simplify under-hood packaging, and reduce maintenance costs. The twin-scroll design improves exhaust-pulse efficiency and speeds up turbo spool, a move BMW highlighted when switching from the N54 to the N55 around 2009; some engines in other brands still use two turbos for packaging or performance gains, such as banked layouts in the Audi S4 or Porsche 911.