Air Fuel Ratio is the ratio of air to fuel that is going into the chambers of your engine. It is measured in the exhaust, after the combustion has happened, by measuring how much oxygen is left over after combustion. There is an “ideal” Air Fuel Ratio of 14.7, but that’s for an engine under little or no load. To make power, you need a richer mixture than that. For reference sake, 14.7 is leaner than 11.0. Under power, 14.7 would cause engine damage, especially if you were talking about a boosted application.

High performance engines, depending on whether they have a power adder or not, tend to need to be somewhere in the 13.0-11.5 range when under load. But is there an ideal AFR for an LS junkyard combo? Richard tests several and has some advice. Watch.

Video Description:

TUNING YOUR LS FOR POWER! WHAT WORKS? HOW MUCH TIMING SHOULD I RUN? WHAT A/F SHOULD I RUN? IS 13:1 TOO LEAN? IS 10:1 TOO RICH? HOW MUCH POWER DO I LOSE WHEN I RUN AN LS AT 11.0:1? WHAT HAPPENS IF I MISS MY TUNE? CHECK OUT THIS VIDEO WHERE I RAN A 5.3L ON THE DYNO EQUIPPED WITH A BTR RED HOT CAM. THE MOTOR WAS “TUNED” TO PROVIDE NEAR 13:1 A/F, THEN 12:1 A/F, THEN 11:1 A/F THEN 10:1 A/F. WHAT WAS THE DIFFERENCE IN POWER? I THEN “TUNED” THE IGNITION TIMING STARTING AT 29 DEGREES, THEN 24, THEN 20 AND FINALLY, 17 DEGREES. WHAT HAPPENED TO POWER.