From what I understand, an ideal internal combustion happens with a 1:12.5 gas:air molecular ratio. And these days in modern cars, there are already sensors to adjust the amount of fuel injected to ensure this. So when people tune their engine, what are they changing? Are you going to get any better performance than a 1:12.5 fuel ratio?
In: Engineering
Firstly, the ‘ideal’ aka. stoichiometric air/fuel mixture is 1:14.7 (for gasoline engines), where you have just an exact amount of air to burn an exact amount of fuel, might not always be the ideal mixture for whatever outcome you’re desiring. For example, having excess air usually improves efficiency, but makes certain emissions (nitrogen oxides) worse. Having excess fuel might be necessary to keep engine temperature down, as fuel vaporizing has a cooling effect.
But the more important point is that while there are sensors to adjust the air/fuel ratio, the computer still needs a baseline fuel map to know how much fuel to inject at any given engine speed, since the response from the sensors is not immediate and the engine speed can vary a lot in a short of amount of time, for example when accelerating. Sensors help the most when the engine speed is not changing, such as cruising or idling.
And from the factory, these fuel maps are not often not perfect. Even mass produced engines have variations, and car manufacturers don’t tune the car’s computer for each vehicle. They have a single fuel map that works for all vehicles that use the same engine configuration, and this tune is generally conservative so it’s not squeezing out the full potential of an engine.
Tuners on the other hand will run the car on a dynometer, rev the engine across it’s rpm range, and see if there are rpm ranges where it’s running off the optimal and adjust the fuel map accordingly. They can also adjust when the spark plug fires, which also affects performance and is usually set very conservatively from the factory.
On a modern car on stock equipment a tune usually doesn’t result in huge improvements, unless the engine has been modified. Then a tune is almost mandatory, since while the car’s computer can adjust to a certain point, it’s way easier when the baseline map is set to match the changes made.
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