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Motorcycle dyno tune - Air to fuel ratio

What is a motorcycle dyno tune? What is air to fuel ratio? And is that for us, dual sport lovers, or is it dedicated to power-hungry racing machines?

On such a delicate and nuanced topic, it is very difficult to give definitive answers, and more than that, to each its own. Meaning that if you ask this questions to 100 people, you will most likely get 100 similar, yet different answers, if not completely different ones.

However, the principles and basics are common, and I believe I can share with you some ideas on what an engine re-mapping is, what a power commander purpose is, and get you rolling on some topics you can study more or ask a professional engine tuner, something I'll bluntly say I am not.

Please keep in mind that what I will share are very basic views and explanations on a much more complex topic, aimed solely at helping you understand a bit better what all of this means.

So let us start from the top.

AFR stands for Air to Fuel Ration, and the stoichiometric AFR for petrol is 14.7 parts of air to 1 part of fuel - this being the chemically complete combustion, hence no residue and the lowest emissions.

On a note, different fuels will have different AFR’s as some chemical equations can show.

For a better power ration, you should go more RICH, meaning, a lower AFR. For better fuel mileage, you want to run LEAN, meaning, higher AFR.

Too lean, or too rich will result in engine damage, so it is important to find the sweet spot. And how do we find that? With a dyno run, with a professional reading charts as the bike rolls on a dedicated machine.

He will take into account things such as air temperature, pressure, humidity, spark plug firing timings and many other points.

Today's bikes are smart bikes, and they will read, over many sensors, what your engine is doing, and within limits, adjust the fuel input in order to keep the engine running as close as possible to its designated AFR at all times. That means the AFR serves as a beacon from which the bike guides itself.

Temperature, humidity, air pressure… all will change the way your engine performs. As an example, if you are a more sensitive rider, you may feel the bike running better on a cold night than you will on a warm summer day, meaning that the environment changes went above what your bike's computer managed to self-adjust.

But why isn’t the factory set up the best one and why should we consider change it?

The factory setup is a compromise between the best engine performance and the laws regarding emissions and noise. That is the reason why Power Commanders, Bazzaz's or any other engine tunning devise will have a disclaimer stating “for race use only”, as the laws for racing are not the same as the ones for the street. That, however, has nothing to do with the best performance of your own engine.

That being said, to whom is an engine tune aimed for? To anyone that wants their engine to work at its best, regardless if any other changes like exhausts or different air filters have been done to it.

You want more mileage? Can be achieved. You want more power? Can be achieved. You want to get rid of any power dips you might feel at certain rpm’s? Can be achieved.

Just keep in mind, that changing these parameters, will influence your engine longevity, and if some might be more gentle with the engine, some will be more aggressive and damaging.

On a personal note, if you do get your bike on a dyno and change your engine map, don't stay focused on your hp or torque, as those numbers will vary from dyno to dyno, will change with air conditions, will even change with the tires you used on your run.

Focus on the relative numbers, and if you improve on what you wanted when compared to when you arrived there, may that have been more power, a smoother power line, or a torquier engine, you did well.


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