Quote:
Originally Posted by GREASY_BEAST
You've only thought about half the event. The event goes as follows:
1) Plunger rises
2) Injector line swells
3) Injector opens
4) Injector line contracts (depending on pressure relief through nozzle)
5) Injector closes
6) Injector line swells
7) Plunger descends
8) Injector line contracts
You made it to step 4.
With higher pop-pressure (more spring tension in the injector body due to thicker shim) the injector closes sooner, thus causing the line to swell and not allow as much fuel in. Keep in mind that even with only 5psi in the line, the line DOES swell, just not very much. Therefore, if you increase the pop pressure, the line has more volume when the injector closes, therefore, because the plunger only pushes a finite volume, the line "absorbs" a greater quantity of the fuel.
Again, this is all completely theoretical and if you really want to find out anything meaningful, dyno testing is probably the best method.
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I was not describing all the steps it took to inject the fuel; I picked things that I believe would change the fuel quanity if the pop pressure/opening pressure if the injector nozzle would possibly effect.
1) Plunger rises- The pluhger rises but will not start injection fuel until the fuel feed port/hole in the side of the element is closed (causing the begin of injection/port closing). The begin of injection depends on what position the "Helix" on the plunger is in.
6) Injector line swells- The injector line dose not swell again as the delivery valves have a portion on them that produces "fuel retraction" in the fuel lines which causes an abrupt cut off of the fuel and even pulls some fuel backwards to. Partly to cut off the fuel abruptly and decrease the pressure wave. The result is that there should be no swollen hard line.
7) Plunger descends- Ounce the delivery valve closes (this happens before the plunger decends) the decending plunger has no effect on what is going on in the injector hard lines.
8) Injector line contracts- Again when the delivery valve closes the the injector hard line is already contracted due to the fuel retraction feature built into the delivery valve.