Author: Todd Marcucci
Programming the AFC
In general, with a stock or mildly modified car (bolt-ons), you will find that the factory mapping is good at lower RPMs, or below VTEC in VTEC Hondas, and then the mapping becomes progressively more rich on the top end. Depending on your modifications this may vary greatly, for instance most turbo/SC vehicles will need a much richer air/ fuel mixture than a naturally aspirated (NA) vehicle. Also, the factory mapping is rich for a reason- this provides for a much greater range of operation, such as operation in very cold temperatures at sea level (more fuel injected) and also in very hot weather at higher altitudes (less fuel injected). Honda has to make sure the car will run well independent of whether it is in Phoenix in summer or Minneapolis in the winter.
Consult a local, experienced tuner for the most appropriate air/fuel ratio based on your vehicle and your driving, and tune the VAFC appropriately. As a point of reference the factory mapping will oscillate around 14.7 (stoich) when closed loop (may vary from 14.5 to 15.0) depending on the situation and run as rich as 11:1 when starting or in WOT/VTEC at or near the rev limiter. I would not recommend NA vehicles going any leaner than 13.5:1 for reliability's sake (can lead to detonation or burning valves) or FI vehicles going any richer than 11:1 (it will likely be too hard to ignite the air/ fuel mixture and cause stumbling).
This page last updated 5/15/07.