What's the best AFR?
25 Jun 2025
Another common question that is asked is "what is the best AFR to use for my engine?" The following chart s is a general guideline AFR/Lambda Best Practices. Unless its a Subaru...you might want a little more fuel in boost ha!
- Target AFR: Aim for 14.7:1 (Lambda 1.0) at idle/cruise for gasoline; 12.5-13.5:1 (Lambda 0.85-0.92) under load/tuning.
- Monitor Lambda: Use wideband O2 sensor for accurate readings; Lambda is fuel-type agnostic (1.0 = stoich).
- Check Conditions: Ensure engine is warm, no leaks, and sensor is calibrated.
- Log Data: Record AFR/Lambda during runs to spot trends or issues.
- Safety Margin: Lean mixtures (Lambda >1.1) risk detonation; rich mixtures (Lambda <0.85) protect under high boost.
Target AFR Chart for Gasoline Engines
|
Driving Condition |
Target AFR |
Lambda |
|---|---|---|
|
Idle |
14.7:1 |
1.0 |
|
Cruising |
14.7:1 |
1.0 |
|
Light Acceleration |
13.5-14.5:1 |
0.92-0.98 |
|
Heavy Acceleration |
12.5-13.5:1 |
0.85-0.92 |
|
Turbo/Boost |
11.5-12.5:1 |
0.78-0.85 |
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