Split fuel rail theory
 

Why did Mazda decide to split the fuel injection locations into two different spots?

Primaries inject right in the center iron, close to the port.
Secondaries inject halfway up the lower intake manifold.

I thought fuel injection closest to the combustion area is best.?

Must have posted this in the section no one reads or something. :scratch:

As the primary injectors are used at light load/idle, they need to be close to the port for proper fuel mixing and to avoid large amounts of fuel clinging to the runner walls. The secondaries are brought in at higher RPM when airflow is high, so they are spaced farther from the port so that fuel atomizes better into the air stream.

And the reason that the staged injection system is used in the first place is that big injectors at the time weren't very controllable to inject small amounts of fuel, so staging them was the logical solution.

Gotcha. Makes sense.