To maximize efficiency on the GTS, Porsche redeveloped the intake manifolds. At high engine speeds and loads, this new pressure design offers higher thermodynamic efficiency. Porsche has restricted the intake size, and allowed the air to mix between pipes. This may sound counter productive, but this is one of the tricks Porsche used to maximize performance in the GTS models.
Stock replacement intake manifolds for 718 Boxster / Cayman GTS models. We're not sure, but this could be an upgrade for standard 718 models. Installation is pretty intense, requires removing the airbox and intercooler.