Spark advance explanation

Hi, why the spark advance changer like the graph attached through the rpm range. Why we have more advance, then goes down and up again..

Regards

When you are tuning you're trying to create the maximum safe cylinder pressure, the engine is an air pump, and as such is only truly efficient at one rpm. With this in mind if you look at your torque graph from a dyno you'll see there is a peak, this will be where the bottom of the dip is in the timing which will also be the peak efficiency of the engine (highest VE), as you go away from this point on either side you'll be able to add more timing in to ignite your fuel mixture earlier to try and maintain the same cylinder pressure achieved at your peak torque.

I understand that part, what I´m trying to understand is the grapho shown in the pictures you see timing advance on the right , it goes up, then you take out advance and then you give more advance again. Why is this happening

As you pass the point of peak VE the engine becomes less efficient at generating its peak cylinder pressures and as such you fire the spark sooner to give more time for the flame front to try to generate the same cylinder pressures.