Air-Fuel Ratio (AFR)

The mass ratio of air to fuel in the combustion charge, the core metric you tune fueling against.

AFR is the ratio by mass of air to fuel entering the cylinder. For pump gasoline, 14.7:1 is stoichiometric (complete combustion); numbers below that (e.g., 12.5:1) are rich, above it are lean. AFR matters because it directly drives power, heat, and engine safety: too lean under load causes detonation and melted pistons, while a controlled rich AFR cools the charge and protects the engine at high cylinder pressure. Tuners typically target roughly 12.8-13.2:1 at wide-open throttle on a naturally aspirated build, richer still under boost. In HP Tuners VCM Scanner, log AFR from a wideband (a real measured value), not the factory narrowband. In VCM Editor you set targets indirectly through the commanded fuel and PE tables. Remember commanded does not equal delivered: always confirm with the wideband what the engine actually got before trusting the calibration.