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.
Demo build: this panel is locked
The knock-detection panel is available in the full game. See Demo vs Full Version.
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:
| Advance over the limit | Knock index | Meaning |
|---|---|---|
| 5° | 1.0 | audible |
| 10° | 4 | severe |
| 15° | 9 | catastrophic |
How each factor moves the knock limit:
| Factor | Effect on the limit |
|---|---|
| Octane | Base = 40° + (RON − 87), so +1° per octane point |
| Compression ratio | −2° per 1:1 above 8:1 |
| Load (MAP ÷ barometric) | −18° × (load ratio)² — about −1.6° at idle load, −18° at full NA load |
| Coolant (ECT) | −0.15° per °C above 90 °C |
| Intake air (IAT) | −0.08° per °C above 30 °C |
| Mixture (lambda) | Rich raises it by up to 3° (at λ 0.85 or richer); lean lowers it by up to 8° (worst near λ 1.4); beyond λ 1.7 knock is impossible — nothing burns |
| RPM | Low RPM is worse: −2° at 1000 RPM, −1° at 2000, 0° at 3000, and +2° (better) from 5000 RPM up |
| Bore | −0.15° per mm above 86 mm (the V8's 99 mm costs about 2°) |
Why it matters¶
Knock destroys engines. Detonation wears the block, the head and especially the pistons, which take 2.5× the block's rate. 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.
Knock control. To protect the engine, Engone runs closed-loop knock control:
- Knock is only evaluated above 1200 RPM.
- Fast retard — once the sensor reading exceeds 0.3, timing is pulled at 3 → 12 °/s (more knock means faster), capped at 15°.
- Slow recovery — after a 0.5 s hold, advance is eased back in at 0.5 → 1.5 °/s. It scales with RPM, and is slower at low RPM.
- There is no knock during any combustion cut — DFCO or either kind of rev-limiter cut. No flame, nothing to knock.
The ECU's retard is a safety net. The damage is calculated from the real knock, not the sensor's.
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 coolant and intake air, and a lower compression ratio. Pulling advance keeps you under the limit.
Player controls — IGNITION page → right column → KNOCK DETECTION card:
FUEL OCTANE(87 / 91 / 95 / 98)SENSITIVITY(0.5–2.0) — multiplies what the ECU sees. Too low and the ECU misses real knock — and the engine still takes the damage. Too high and sensor noise above about 4000 RPM (full by about 7000) triggers false retard.CUTOFF RPM(0 = off) — turns the sensor off above that speed: retard freezes, and real knock continues unseen.
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 conditions, lower octane, or a higher compression ratio all lower the knock limit. When any of those change, pull timing or richen before you push power.
On a boosted engine
Engone currently simulates naturally aspirated engines only. For background: a boosted engine packs far more air into the cylinder, so the tune changes — target lambda moves richer (to cool the charge and protect against knock), ignition advance comes down in the boosted cells, compression ratio is usually lowered, and higher octane matters more. See Boosted Engines (Background).
In the game¶
In the KNOCK DETECTION card the live readouts are KNOCK (the index), RETARD (degrees pulled),
EVENTS (a count), SIGNAL (CLEAN or NOISY) and a bar. Warning light 4 lights when the knock
index passes 0.5 (see Warning Lights & Engine State). Detonation
wears the engine — see Damage & Wear.