Knock & Detonation¶
The unburned end-gas auto-igniting on its own — a damaging hammer-blow on the piston. The ECU retards timing fast to escape it.
What it is¶
Normally the spark lights a flame that sweeps smoothly across the chamber. Knock (detonation) happens when the last pocket of unburned mixture — the end-gas — gets so hot and pressurized that it auto-ignites on its own, before the flame reaches it. The two pressure waves collide violently, producing the characteristic metallic rattle and a sharp spike that batters the piston and rings.
In Engone a knock index rises quadratically as spark advance pushes past the knock limit. That limit is set by the combination of: octane, compression ratio, load, intake and coolant temperature (IAT/ECT), lambda, and RPM.
Why it matters¶
Knock destroys engines. Sustained detonation hammers piston crowns and ring lands until something fails. Because the knock index climbs quadratically, a tune that's a little too aggressive isn't a little risky — it's rapidly dangerous as you add advance or load.
To protect the engine, Engone runs closed-loop knock control:
- Fast retard when knock is detected — pulling timing out at roughly 3–12°/s.
- Slow recovery afterward — easing advance back in at about 0.5°/s once knock clears.
How to tune it¶
Stay below the knock limit by design, not by relying on the controller to save you. The levers that raise the limit (buy margin): higher octane, richer mixture, cooler intake air, less advance, lower boost.
Watch out
Knock control is a safety net, not a tuning tool. If it's constantly retarding to hold the engine together, your timing table is too aggressive for the fuel and conditions — fix the table.
Rule of thumb
Hot day, low octane, or more boost all lower the knock limit. When any of those change, pull timing or richen before you push power.
In the game¶
The Ignition page has an octane dropdown and a knock-sensitivity slider, plus a live knock indicator. Watch it while advancing timing or raising boost.