Quote:
Originally Posted by jlh335i
^ I was refering to the orientation of the exhaust manifold that easily distinguishes any twin scroll setup from a traditional turbo. A twin scroll turbo system begins with a manifold that routes exhaust gases according to the firing order of the engine.
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Twin scroll refers to the design of the turbine housing with two exhaust channels in the turbine housing itself.
On a I6, the routing of the exhaust manifold is similar both on the N55 single turbo twin scroll and the S55 twin turbo mono scroll setup. On a I6 you want to route the exhaust from cyl 1-3 and 4-6 into either each turbo (as per N54/S55) or to each of the scrolls in a twin scroll turbo (as per N55). On a N55 exhaust manifold, it's not really outwardly visible that there is a twin scroll turbo. It looks like a common I6 exhaust manifold leading to one turbo, but with cyl 1-3 separated from cyl 4-6
internally at the mounting flange to the turbo.
However on the I4 N20, you want cyl 1-4 and 2-3 routed together:
