AFR ↔ Lambda Converter
Convert air-fuel ratio to lambda for any fuel — petrol, E85, methanol.
Get a proper dyno calibration?
How it works
Lambda (λ) is fuel-agnostic: λ = 1.00 is always the perfect (stoichiometric) mixture, below 1 is rich, above 1 is lean — no matter what fuel you burn. AFR is fuel-specific, so a “safe” AFR number on petrol means nothing on E85. That’s why tuners think in lambda and only convert to AFR for a given fuel.
Enter a lambda and pick your fuel to get the equivalent AFR. Typical wide-open-throttle targets are around λ 0.80–0.88 for boosted petrol (richer = cooler, safer), near λ 1.00 for cruise, and similar lambda values on E85 — but a very different AFR number (because E85’s stoich is 9.76, not 14.7).
Reading and holding the right lambda under load is the core of safe tuning. On the dyno we watch lambda against knock and load, not a single AFR number.
These figures are engineering guidelines to help you plan. The reliable number always comes off the dyno — that's how every DMS build is proven.
FAQ
Why do tuners use lambda instead of AFR?
Because lambda is the same across all fuels — λ 0.85 is the same relative richness on petrol, E85 or methanol. AFR changes with fuel, so it’s easy to misread. Lambda removes that ambiguity.
What lambda is safe under boost?
For boosted petrol, roughly λ 0.80–0.86 at full load is a common safe, power-making target — richer runs cooler. The exact figure depends on the engine, fuel and timing; we set it on the dyno.
What’s the AFR for E85?
Stoichiometric E85 is ~9.76:1, so a power target of λ 0.82 is ~8.0:1 AFR on E85 — a number that would look dangerously rich on petrol but is correct for E85.