Jim is 100% correct.

Injectors have a permenant 12v live and are operated by the ECU earthing them out.

Low impedence injectors require a lot of voltage to operate them so by doubling up you will be doubling the voltage the ECU has to ground.
Forget about the fact you will half the open duration, you will still be doubling the power the drivers have to put to earth.


Also the idea if 8 injectors is so that at low revs only 1 set operate, this helps prevent fuel drop out in the slow moving intake air.