Octane¶
A fuel's resistance to detonation. Higher octane raises the knock limit and lets you run more advance — match it to your compression and boost.
What it is¶
Octane (RON) rates how well a fuel resists auto-igniting under pressure and heat — its resistance to knock. It is not a measure of energy content; a higher-octane fuel doesn't carry more power on its own. What it does is raise the knock limit, giving the tune room to use timing that would detonate on lower-octane fuel.
In Engone, octane shifts the allowable advance by roughly ±0.5° per octane number relative to a 95-octane reference, and correspondingly raises the knock limit.
Why it matters¶
Octane and the engine must be matched:
- High compression or boost raises cylinder pressure and temperature, which lowers the knock threshold — these engines need high octane to run their intended timing.
- Low compression, naturally aspirated engines gain little from premium fuel; the knock limit isn't what's holding them back.
Run too low an octane for the build and you're forced to pull timing (losing power) or risk knock. Run higher octane than needed and you've simply spent money for advance you can't use.
How to tune it¶
Pick the octane that matches your compression ratio and boost, then tune the timing table to it. If you switch to a higher octane, you can add advance toward MBT; on lower octane, you must retreat.
Rule of thumb
Set octane to match the fuel you'll actually run, then tune timing. Tuning on premium and then filling with regular is a recipe for knock.
In the game¶
Octane is selected from the dropdown on the Ignition page. Changing it shifts the knock limit, so re-check your high-load timing cells afterward.