Air/Fuel Ratio Limits Chart - AFR for Best Power, Torque & Economy

This document is a concise reference chart titled "Air/Fuel Ratio Limits" listing nine gasoline air/fuel ratios and their operational significance for engine tuning. It spans the full practical operating range: 6.0:1 is identified as the rich run limit and 18-22:1 as the lean run limit. Between these extremes, 9.0:1 corresponds to low power with black smoke; 11.5:1 is described as rich, giving best torque at wide-open throttle (WOT); 12.5:1 is called safe, providing best power at WOT; and 13.2:1 is lean, best torque at WOT. The chemically ideal (stoichiometric) ratio is listed as 14.7:1. For part-throttle operation, 15.5:1 is described as lean light load, and 16.2:1 as best economy. A reader can use this chart to understand target air/fuel ratios for different driving conditions—maximum power tuning at WOT versus fuel economy at part throttle—and to recognize the boundaries beyond which an engine will not run. The chart is generic to gasoline engines and contains no vehicle-specific year, make, model, or part number information, though it was uploaded to a 1990 Ford Bronco documentation album alongside EFI and tuning references.