How it works:

An engine under heavy load will ping/knock sooner (lean mixture) than an engine under a light load (rich mixture). If we give more pre-ignition to an engine under light load, the efficiency will increase and as a result the engine will use less fuel.

The vacuum in the intake manifold is a measure of the load on the engine. (full throttle up the mountain = throttle valve open –> very little negative pressure. Half throttle down the mountain = throttle valve partially closed –> a lot of negative pressure/vacuum). This means that if a vacuum is created in the intake manifold, we can advance the ignition slightly.

Why do you want this:

In summary, by using vacuum advance we can reduce fuel consumption in partial load, the combustion will be cleaner and the efficiency will improve.

As an extra for the more advanced technician:

Altitude compensation: The 123ignition uses absolute pressure, (MAP or Manifold Absolute Pressure) to adjust the ignition timing. This compensates for thinner air (lower air pressure) at higher altitudes. The oxygen concentration per volume of air decreases with altitude, which results in a richer fuel mixture that takes longer to ignite. In these conditions, more pre-ignition is needed for optimal combustion.