Twin-scroll turbine housing
Keeps exhaust pulses from different cylinders apart until the turbine.
On the hot side of the turbocharger, fed by a divided exhaust manifold.
Grouping cylinders whose pulses do not overlap gives the turbine sharper energy at low engine speed.
Two lanes merging just before a toll booth.
Cracks or leaks in the manifold or housing can cause ticking, smell or reduced boost.
Filters follow the vehicle service schedule; ducts and boost hardware are inspected for condition, sealing and operation.
A hose or filter is generally simpler to service than a turbo assembly. Access and diagnosis can dominate cost.
The N55 and B58 inline-sixes feed cylinders 1–3 and 4–6 into separate scrolls.
BMW combustion models; boost hardware applies to turbocharged engines only.