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Exhaust Pops & Afterfire

Unburnt fuel and air meeting heat in the exhaust and igniting — the burbles and bangs of a tuned car. Engone simulates it physically, so nothing is scripted.

Demo build: this panel is locked

The DFCO DELAY and CUT TYPE controls are available in the full game. See Demo vs Full Version.

What it is

Unburnt fuel and air meeting heat in the exhaust ignite, producing burbles and bangs. Engone simulates this physically in three zones — the header, the catalyst / mid-pipe, and the silencer — so nothing is scripted.

Why it matters

What makes pops:

  1. DFCO delay — fuel keeps flowing for up to 3 s after lift-off, then the cut leaves air in the pipe.
  2. Valve overlap × overrun vacuum — a big cam burbles on lift but stays clean at WOT.
  3. CUT TYPE = SPARK on the rev limiter — fuel keeps flowing unburnt into the exhaust and it bangs repeatedly.
  4. Misfires (lean or rich) dump fuel into the exhaust.

What stops them:

  • A catalyst — a hot cat quietly burns small amounts of unburnt fuel, so a stock car never pops.
  • A stock silencer — volume and damping.
  • Cold exhaust — no pops below about 400 °C wall temperature.
  • Rich WOT — no free oxygen.
  • DFCO itself — only air, no fuel.

How to tune it

For pops you need fuel, oxygen and heat in the pipe at the same time, and an exhaust that lets them out — a decat and a resonator, for example.

Rule of thumb

Fuel + oxygen + heat + an open exhaust. Take any one away and the pops stop.

In the game

Set DFCO DELAY and CUT TYPE on the IGNITION page → REV LIMITER card. Set the exhaust parts (catalyst and silencer type) on the SETUP page — see Exhaust Header.