Wideband Air-Fuel Ratio Devices: what you need to know!
We always hear tuners talk about using a "wideband" to tune our "afr's" and for most, we leave it up to the tuners; the mad scientists that they are, to carry on their esoteric speak.
But jargon aside, we believe it is important to have an understanding and also an appreciation of the device known as a "Wideband AFR Controller".
Well, in the first instance, the reference to it is incorrect. A wideband device is not capable of controlling anything. It is simply a device that monitors and in some cases, displays what the ratio of air and fuel is during the combustion process.
What is this ratio and why is it important?
All internal combustion engines produce power by mixing a given quantity of air with a given quantity of fuel, pressurizes it and ignites it at a precisely calculated moment and voila! Combustion! This quantity is calculated as fourteen (14) parts (or to be atomically correct lbs.) of air to one (1) part/lb. of fuel. This would then present an air-to-fuel ratio of 14:1. Most, if not all naturally aspirated engines are designed to consistently combust the air/fuel mixture in this ratio.
Forced induction (aka turbocharged or supercharged) engines are designed by the manufacturer to keep an approximate of this 14:1 ratio on idle and on negative pressure (vacuum). As the engine starts building positive pressure, known as boost, the engine control unit is pre-programmed to change the mixture, by adding a bit more fuel. While the exact ratio may vary, it is said that optimal combustion occurs at an air-to-fuel ratio of around 12:1 and so this figure is used as a point of reference, although many manufacturers, with safety and engine longevity in mind, would factory tune an engine to air-to-fuel ratios much lower than this, under boost.
What causes this ratio to be altered?
Remember when our mechanics advise that ever so often a "tune-up" is needed on our engines? Well, this is so that nothing, such as a clogged fuel injector or dirty air filter would prevent variances in the 14:1 ratio large enough to affect our engine's performance.
However, in our nature of being human, we always want better, and this is also true of performance. For many, factory performance just does not cut it, so we go about buying bolt-on parts that promise power gains, or start ripping open engines and grinding here, polishing there etc. All of these "modifications" have a basic effect on an engine...it changes the way in which an engine produces power. Power is simply the amount of energy produced in a given amount of time.
How then do we make more power?
Simple....since energy produced is a factor of how much air and fuel are combusted, then we either increase the volume of air and fuel in each cycle of combustion or we increase the amount of combustion cycles (known as Revolutions Per Minute or RPM's). This article concerns only the first method of increasing power.
So what happens when the ratio is altered?
Well, the ratio of 14:1 (or to be precise, 14.7:1) is known as a sSTOICHIOMETRIC ratio or in short, "STOICH". If this ratio is altered so that there is a relatively greater amount of air than fuel in the mixture, this condition is known as a LEAN mixture. If the ratio is altered in the other direction, that is, more fuel than air, the mixture is said to be "RICH".
For most engines, richness up to a certain point has little effect on an engine's performance (in the short to medium term). However, a lean mixture is a much more undesirable condition and with every incremental combustion cycle, is dangerous to an engine's components. This is because a lean mixture produces much more heat than a stoich or rich mixture, which could lead to meltdown of the components in an engine's combustion chamber, including the chamber walls itself. Furthermore, a lean mixture, when combusted, does not produce as much power as a stoich or rich mixture.
What is a wideband AFR device?
It is a monitoring device which utilizes an sensor that analyzes the spent combustion gases (exhaust gas), and determines how much oxygen is present. Since oxygen is the main combustible element in air, analyzing how much of it is present AFTER combustion, tells how much was used DURING combustion! The sensor is connected to a neat little electronic device that analyzes the sensors reading's and then displays the results as a ratio of air to fuel. Most units are calibrated to display a figure that is always relative to one (1), for ease of use. Some are capable of logging captured data to some storage device via software, such as a laptop or PDA.
Who needs a wideband and why?
At Science Of Speed, we strongly recommend that any owner of a turbocharged or supercharged engine have one of these devices permanently installed in your vehicle, especially if you are the type to toy with air/fuel controllers, piggyback ecu's and bigger turbos. These devices, as mentioned above, physically alter the air-fuel ratio of your combustible mixture. It is important therefore that you monitor the air to fuel ratios to ensure that your mixture does not get overly rich, or more dangerously, overly lean. Personally, we can attest to the usefulness of these devices, as on more than one occasion, it has saved our engines.
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