AFR and the importance of monitoring...
07/04/2020 4:34 pm
Who doesn't love the look of aftermarket gauges? All the needles and lights that give off that cockpit like vibe that brings out the Paul Walker in all of us. The looks are cool and all but what does it all mean? Well, depending on the application it could mean a few different things. Here, we like boost, so we will keep it in relation to forced induction. The two most popular gauges for turbo systems are "Boost", of course, and more importantly Air/Fuel ratio.
What is air/fuel ratio? Air/fuel ratio is an important measure for both emissions and performance-tuning reasons. If exactly enough air is provided to completely burn all of the fuel, the ratio is known as the stoichiometric mixture, or "stoich". Ratios lower than stoichiometric (14.7) are considered "rich". Rich mixtures are less efficient, but may produce more power and burn cooler. Ratios higher than stoichiometric are considered "lean." Lean mixtures are more efficient but may cause higher temperatures, which can lead to the formation of nitrogen oxides.
A stoichiometric mixture burns very hot and can damage engine components if the engine is placed under high load at this air/fuel mixture. High temperatures at this mixture causes detonation of the air/fuel mixture while approaching or shortly after maximum cylinder pressure is possible under high load. This is commonly referred to as knocking or pinging. This detonation can cause serious engine damage as the uncontrolled burning of the fuel air mix can create very high pressures in the cylinder. Stoichiometric mixtures are only used under light to low-moderate load conditions, like idling or cruising. For acceleration and high-load conditions, a richer mixture is used to produce cooler combustion products and so avoid overheating of the cylinder head, preventing detonation.
Engines with forced induction such as turbochargers and superchargers typically require a richer mixture under wide open throttle than naturally aspirated engines due to the increase of power demand. Forced induction engines can experience catastrophic failure by burning too lean for too long. The leaner the air/fuel mixture, the higher the combustion temperature is inside the cylinder. Too high of a temperature will destroy an engine resulting in melted pistons and valves. While not as detrimental, a richer air/fuel mixture can result in a lack of engine performance and excess engine wear. Common causes of a lean mixture range from vacuum leaks or a fuel system issues to bad gas. Common causes of a rich mixture range from worn our spark plugs or faulty O2 sensors to EVAP system issues.
When choosing a AFR gauge, we highly recommend using the X-Series digital by AEM Electronics. Not only is it one of the quickest gauges on the market, it also fully integrates into the HP Tuners VCM Scanner software pulling live data via the OBD II port right into the datalog.