Fuel, Octane & Unleaded Conversion
U.S. pump octane is the Anti-Knock Index, AKI = (RON + MON) ÷ 2. Octane requirement rises with compression ratio.
Octane Requirement by Compression Ratio (iron heads, approx.)
| Compression Ratio | Min. Pump Octane (AKI) |
|---|---|
| 8.0:1 and below | 87 |
| 8.5–9.0:1 | 87–89 |
| 9.0–9.5:1 | 89–91 |
| 9.5–10.0:1 | 91–93 |