Exhaust Header¶
Primary length and collector design tune exhaust scavenging — helping pull spent gas out and fresh charge in. The catalyst and silencer shape the sound and decide whether the exhaust can pop.
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.
Two properties are also modelled:
- Catalytic converter — present or absent.
- Silencer type — straight pipe, resonator, sport or stock.
They mainly shape the sound and decide whether the exhaust can pop and burble — power is governed by the header's back-pressure and scavenging, not by these (see Exhaust Pops & Afterfire). The V12's Race Decat Headers have no cat and a resonator-type silencer; the standard I4 and V8 manifolds keep the cat.
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.
- The collector type and the number of primaries per collector feed the scavenging and the sound.
How to tune it¶
Target the same RPM band as your cam and intake: 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 is the EXHAUST HEADER dropdown on the SETUP page and adjusts the engine's real
VE. After swapping it, re-tune the VE table.