There are a lot of threads about various tuning devices so I figured I would start one on the basics of how an internal combustion motor is tuned. Please note this is about basic tuning. If others would like to chime in with specific details about the devices available, please feel free to do so.
The two key elements of a good tune are the air fuel ratio (AF) and timing. Both of these elements must be correct for the circumstances the engine is under at all points in time. These generally include RPM and "load." Load is how far the throttle is open. There is another important factor called volumetric efficiency (VE). VE is how much your cylinders fill with air and is given in percent.
The stoichiometric point for gas and air is 14.7:1. This means that the fuel molecules and O2 molecules are in perfect balance. There will be times when a richer AF ratio is required (heavy load and high VE) and times when a lean AF is used to save gas (light cruising). If the AF is too lean under heavy load - especially where VE is highest, detonation can occur. On the other hand if the AF is too rich, the fuel will not burn properly and power will be lost. The rule of thumb is that the most HP can be produced at 12.5:1. This is where timing can be advanced the most without detonation.
We hear a lot of talk about creating a lean condition by adding aftermarket parts. In fact, this may be a lean condition or may be a change in VE causing slight detonation due to increased compression. Either way it must be corrected and that is where these tuning devices come into play.
Timing plays a crucial role in achieving power. The object is to advance your timing as much as possible without causing detonation. Things to take into account are AF ratio, because a lean mixture will burn faster than a rich one, and VE because the higher your engine compression, the faster combustion will occur. Increasing air flow of a motor means you are increasing VE which affects the amount of timing you can run at a given RPM and load range.
VE, RPM & Load:
The VE of a motor changes greatly depending on RPM and load. ECU software generally has tables with RPM on one axis and load on the other. Each cell represents a given RPM and load. And for each cell, there will be a given VE. These three things must be taken into account when determining what the AF should be at that point as well as timing. Getting this all perfect is the goal of tuning and is best done on a dyno.
Most cars have auto tune. In cars, this is called "open loop." Generally, the ECU gets info from sensors such as an AF sensor and sometimes a knock sensor. Over time these ECUs "learn" and tweek the tuning for the conditions and driving habits. Generally, open loop is used to reduce fuel consumption and emissions. Under heavy load, a car motor will enter "closed loop." In closed loop, the ECU drops the info from the sensors (not knock sesnor) and uses the information stored in the tables. Generally, open loop is not considered adequate for high load WOT conditions and therefore not used as a tuning mechanism. One reason micht be because regardless of how many times your ECU samples a wide band O2 sensor, the sensor can only measure at a given rate and it probably isn't anywhere near fast enough to acturatly assign values all along the RPM and load range.
So, if you are just wanting to maintain a decent AF ratio (assuming that is your problem) and auto tune device may work. But the proper way to tune a motor is to buy a device that controlls AF and timing, put the bike on a dyno and have it properly tuned.
By the way, pretty much all tuning problems can be masked by running a rich AF ratio. But that may come at the expense of lost power. Never assume that because adding fuel made your bike "run right" you have properly tuned your bike.
Like a richer AF ratio, high octane ratings slow the rate of combustion. So, the higher your RON, the more timing and the leaner AF ratio you can run at a given RPM / load. This translates into more power. Also, combustion of lean AF mixtures can actually release more energy where as rich mixtures can result in unburned components and lost power.
If you want to make your bike run ok after putting on a cool sounding pipe, an auto-tuning device that enriches your AF will work. But, if you want a proper tune that will result in more power, get a device that controls both fuel and spark and have your bike properly dyno tuned.
Well, that is a start. Gotta get to work. I hope people find this useful.