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Exhaust Header

Primary length and collector design tune exhaust scavenging — helping pull spent gas out and fresh charge in. Must match the intake type.

What it is

The exhaust header carries spent gas away from the cylinders, and like the intake it tunes pressure waves. Key parameters: primary length and diameter, collector type, back pressure, and how many primaries feed each collector. Good design uses the exhaust pulse from one cylinder to help scavenge another.

Why it matters

  • Scavenging — well-tuned primaries create a low-pressure wave that helps draw exhaust out and fresh charge in during valve overlap, lifting VE in a particular band.
  • Primary length sets where that help arrives: longer primaries scavenge low, shorter primaries high — the same low-vs-high trade as intake runners.
  • Back pressure that's too high simply chokes the engine, hurting VE everywhere.

Must match the intake type

The header must be compatible with the intake setup — a naturally aspirated header and a turbo header are not interchangeable. A turbo exhaust feeds the turbine; an NA header is tuned for free-flow scavenging. The build enforces this.

How to tune it

Target the same RPM band as your cam and intake. For a turbo build, use the turbo-compatible exhaust; for NA, tune primary length to the band you want to fill.

Rule of thumb

Intake, cam, and header should all be tuned for the same RPM band. A high-RPM cam with low-RPM runners and a restrictive header wastes its potential.

In the game

Header selection on the Setup page adjusts the VE curve. Incompatible intake/exhaust combinations (NA vs turbo) are blocked.