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blue2000s · 12-08-2009, 05:43 PM

14.7:1 is the ratio of complete combustion of gasoline in air in an ideal situation. Meaning that all the fuel is atomized and there's enough time and conditions are perfect when the flame front comes through.

Obviously, nothing's perfect. It takes more fuel than the ideal amount to account for non-atomized fuel and incomplete combustion.

Richer combustion also serves to lower the temperature of combustion products, helping with the reliability of valves and valve seats. At full load, there's alot of energy being released and for the best combustion and the most reliable engine, AFRs of 12:1 are better. Turbos usually run even more rich at full load. Not to mention that spark timing is set to coincide with an expected fuel ratio.

The best ratio depends on the engine as airflow patterns and mixing are always different. That's what dyno runs are for.

At light loads, where there's less stresses on the engine and mixing is better, ratios closer and sometimes even leaner than 14.7:1 are possible.

Running 14.7:1 and higher at full throttle is bad for your engine.

12-08-2009, 05:43 PM	#2
blue2000s Porscheectomy Join Date: Mar 2006 Location: Seattle Area Posts: 3,011	14.7:1 is the ratio of complete combustion of gasoline in air in an ideal situation. Meaning that all the fuel is atomized and there's enough time and conditions are perfect when the flame front comes through. Obviously, nothing's perfect. It takes more fuel than the ideal amount to account for non-atomized fuel and incomplete combustion. Richer combustion also serves to lower the temperature of combustion products, helping with the reliability of valves and valve seats. At full load, there's alot of energy being released and for the best combustion and the most reliable engine, AFRs of 12:1 are better. Turbos usually run even more rich at full load. Not to mention that spark timing is set to coincide with an expected fuel ratio. The best ratio depends on the engine as airflow patterns and mixing are always different. That's what dyno runs are for. At light loads, where there's less stresses on the engine and mixing is better, ratios closer and sometimes even leaner than 14.7:1 are possible. Running 14.7:1 and higher at full throttle is bad for your engine. Last edited by blue2000s; 12-08-2009 at 05:53 PM.