Simultaneous vs Alternating

[Philip Lochner]

"There is some benefit to choosing 2 squirts/alternating for port injection, since only half of the injectors fire at once, the pressure drop in the fuel rails is reduced and the fuelling is more consistent. "

For V8:
Is it ONLY 2 squirts that will have half the injectors firing at once? Will 4 squirts/alternating not also have half the injectors firing at once?

[Bernard Fife]

Philip,

Yes, 4 squirt alternating, 8 alternating, etc., have the same advantage as 2 alternating in that they distribute the fuel pressure more evenly in theory.

The higher squirt counts have no additional benefit over 2 squirts though, and they eat into the injection time with the extra open times. This increases the duty cycle for the same amount of fuel, and means the engine will run out of fuel sooner. So for port injection, 2 squirts/alternating is generally the way to go.

TBI is another story entirely, of course.

Lance.

[Philip Lochner]

The higher squirt counts have no additional benefit over 2 squirts though, and they eat into the injection time with the extra open times.

Thanks Lance

Is it not possible that with more squirts one could have slightly better evaporation of fuel?

[Minami Kotaro]

My experience with alternating vs. simultaneous is this:

I have a horizontally opposed engine. When I had both injectors on the same side on the same circuit (1+2, 3+4), I found that two squirts simultaneous provided the smoothest idle and low-end. When I had two injectors on opposing sides on the same circuit (1+3, 2+4), I found that two squirts alternating provided the smoothest idle and low-end.

Alternating vs. simultaneous didn't make much difference past 2000 RPM or so.

Going with one squirt made the idle and sub-2000 RPM performance very poor. Moving up to four squirts, the engine would barely even run.