| Condition | Lambda | AFR (this fuel) |
|---|
AFR and Lambda Explained
Air-fuel ratio is the mass of air divided by the mass of fuel in the mixture an engine burns. The chemically perfect ratio, where all fuel and air are consumed, is called stoichiometric, and it differs by fuel: about 14.7 to 1 for gasoline but only 9.8 to 1 for E85. Lambda normalizes all of this, so lambda 1.00 is stoichiometric for any fuel.
Rich, Lean, and Why It Matters
A rich mixture has extra fuel and runs cooler, which is why engines deliberately go rich at full throttle to protect against knock and heat. A lean mixture has extra air and improves economy at light load, but under high load it raises combustion temperatures and invites detonation. Tuning is the art of being rich where it matters and lean where it is safe.
Switching Fuels Changes the Numbers
Because each fuel has its own stoichiometric ratio, an AFR that is perfect for gasoline would be wildly wrong for E85 or methanol. That is the strength of lambda: it lets you tune by one consistent scale no matter what is in the tank. This tool converts your measured AFR to lambda for the fuel you select.
Frequently Asked Questions
What AFR should I run at wide-open throttle?
For naturally aspirated gasoline, roughly 12.5 to 13.0 to 1; boosted engines often go richer, near 11.5 to 12.0. In lambda that is about 0.85 to 0.88, which carries across fuels.
Is lean always bad?
No. Slightly lean is efficient at light cruise. Lean becomes dangerous only under load, where it spikes temperatures and risks knock.
Why use lambda instead of AFR?
Lambda is fuel-independent, so the same target works whether you run gasoline, E85, or methanol. It removes the confusion of different stoichiometric ratios.