Air-Fuel Ratio (AFR) is the mixture of air and fuel in your engine. A stock gasoline engine runs around 14.7:1 under normal conditions.
For turbocharged or supercharged engines, AFR is usually richer (lower number) to prevent engine knock and damage under boost.
Lower AFR = more fuel (safer for boost)
Higher AFR = leaner mixture (more efficiency but higher risk under load)
Air-Fuel Ratio (AFR) is one of the most important concepts in engine tuning. It describes the balance between the amount of air and fuel entering an engine. This ratio directly affects performance, efficiency, and engine safety.
A typical gasoline engine runs at a stoichiometric AFR of around 14.7:1, which means 14.7 parts air to 1 part fuel. This is considered the ideal balance for complete combustion under normal driving conditions.
However, performance engines — especially turbocharged or supercharged setups — require a richer mixture (lower AFR value) under load. This extra fuel helps reduce engine temperatures and prevents knocking, which can cause serious engine damage.
For boosted applications, AFR values commonly range between 11.5:1 and 12.5:1, depending on boost pressure, fuel type, and engine setup.
Fuel type also plays a major role in AFR tuning. Ethanol-based fuels like E85 allow for different AFR targets compared to standard pump gasoline because ethanol has different combustion properties and cooling effects.
This calculator helps you estimate a safe AFR target based on engine type, boost level, and fuel choice. While it does not replace professional tuning, it provides a useful guideline for understanding safe operating ranges.
A rich AFR (lower number) is used when an engine is under heavy load, such as acceleration, towing, or boost. This helps protect the engine from high combustion temperatures.
A lean AFR (higher number) is typically used during cruising or light throttle conditions where efficiency is more important than maximum power output.
Finding the correct AFR balance is critical for engine longevity, especially in modified or performance builds.
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