One of the most important things about tuning and your motors safe, efficient and power generating operation is Air Fuel Ratio (AFR). As the name suggests, this is the ratio between the air and the fuel. While a complete burn may be the best for emissions, a slightly lean burn (less fuel) may be even better for fuel consumption and a rich burn (more fuel) may be better for engine cooling and fast moving piston speeds. Both lean and rich burns have their drawbacks though, too lean can cause a burn so hot it's enough to melt engine components while a burn that is too rich can wash out cylinder walls and cause block damage. So why not just tell you the perfect AFR and be done with it? Well, different motor designs and very small differences in manufacturing can mean changes to what AFR is best for your car. As a general starting point most tuners recommend 1 lambda for idle and 0.76 for turboed cars at high rpm on gasoline. A dynometer (machine used to measure power) can be used to then measure the power change when a different AFR is used. Incremental changes to the AFR should then be made until the ideal AFR is reached. It's important to note that different fuels also react differently to different AFRs and that most wideband O2 gauges read in Lambda but display in gasoline AFR. They are therefore still accurate but are not displaying the value most true to the fuel.