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Recommended Air/Fuel Ratio Chart
The following chart may be used as a guideline for baseline tuning of your engine.
The values specified in this chart should provide reasonably safe starting points when
beginning an engine calibration. Once you have tuned your engine to run at or near
these values, you can experiment to see how small changes in fueling impact power,
economy, and drivability.
If you have any questions or concerns about these values or how your combination
will work with these values, you should consult your engine builder or a professional
tuner before you begin. Such factors as fuel octane rating, air temperature, ignition
timing, exhaust configuration, cam profile, compression ratio, and combustion
chamber design all have an impact on the “ideal” air/fuel ratio for your application.
This chart should be considered a guideline ONLY. In addition to air/fuel ratio
information, you should monitor engine temperature, listen for spark knock, and
read the spark plugs to determine a fuel setting that is safe and appropriate.
Suggested A/F Ratios
Engine Type
Idle
Cruise
WOT
Stock - little or no modification
to engine, 87 octane gasoline
14.7:1
14.7:1
12.5:1
Street/Strip engine – naturally
aspirated, performance
camshaft and exhaust, 10.0-
11.0 compression, premium
pump gasoline
14.2:1
14.0:1
12.8:1
Race engine – naturally
aspirated, high lift/duration
cam, 12:1 or higher
compression, high-flow heads
and exhaust, high octane
racing fuel
13.5:1
13.5:1
13.0:1
Turbocharged/supercharged –
stock or mild performance, 6
to 8 psi boost, premium pump
gasoline
14.2:1
13.8:1
12.3:1
Turbocharged/supercharged –
street/strip performance, 10
to 15 psi boost, intercooler,
pump gas with octane booster
or race gas mix
14.0:1
14.0:1
12.0:1
Turbocharged/supercharged –
race configuration, 20-30 psi
boost, intercooled, high octane
race fuel
13.0:1
13.0:1
11.5:1
Turbocharged/supercharged –
race configuration, 20-30 psi
boost, NON-INTERCOOLED,
high octane race fuel
13.0:1
13.0:1
11.0:1
