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
Tuning generally involves more than just changing values. Typically you “tune”after you upgrade parts. For example you may install aftermarket injectors, pistons, exhaust, etc.
If I install aftermarket pistons, intake, and exhaust systems which may allow for a greater quantity of air/fuel to be delivered to the combustion chamber I would need to adjust the software in the main brain of the car to compensate for these upgrades.
Factory specifications include lots of liability “buffers” For example cars built in the US have to adhere to certain environmental laws. You could change specifications to bypass some liability functions. So there are ways to get short term improvements in power. However without upgrading components this kind of adjustment puts you at greater risk for part failure or even breaking the law (depending where you live)
Car makers tune to hit specific efficiency and longevity goals, as well as power. They also tune for driving comfort and lower grade fuel for most non-sports cars.
Air fuel mix isn’t the only knob tuners can tweak. There is also detonation timing and variable valve timing (like Honda’s VTEC).
A tuner going for maximum power will adjust all the variables to make more power in specific RPM ranges, as well as ignoring efficiency. Tuners are also sometimes making changes to take advantage of car modifications like bigger air intakes or fuel pumps, or just changing a car to run better on premium fuel.
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.
Usually you’re changing the fuel/air mix and the ignition timing. These are specific to your exact setup based on a lot of factors from your intake to spark plugs to altitude.
If your goal is performance, the question is *when* do you want that performance. Do you want it when the engine is idling, when it’s at mid throttle, or when its going as fast as it can? And what do you call “performance?” Do you mean max power or max efficiency?
Are you planning to use lower octane gas (cheaper, more forgiving in terms of pre-detonation) or higher octane (more power).
Timing is weird because you want the bang at exactly the right time. Imagine two kids on a trampoline, one double bouncing the other. The bounce has to be at exactly the right moment, right? Same with the bang in each of your pistons. It needs to be at exactly the right moment but the right moment can change at different speeds of the engine.
If you get that bang wrong enough it can mean that you get to see some of the inner workings of your engine… if you can find them wherever they land.
Thanks to electronic ignition, electronic fueling, and better computer technology, you can now tell your engine how to change the way it uses fuel, air, and spark at different times so that you get the most performance (whatever that means to you) when you want it based on your application AND change those parameters when it needs to.
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