Quote:
Originally Posted by Diseasel300
... pop pressure sets the timing ... If the pop pressures are off very far, it will affect the spray pattern and cause uneven power and a rough idle.
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Pop pressure has a very small effect on injector timing. The IP is positive displacement and the fuel is very incompressible, and the tubes very stiff, so the nozzle will open in sync with IP piston motion, i.e. it keeps building pressure until the spring pressure is overcome and the nozzle pops open. To be exact, raising the pop pressure will delay opening, but very slightly and only due to the very slight compressibility in the system (i.e. negligible).
If pop pressure is so critical, why did I notice negligible difference from changing the 3 injectors in my 1984 w/ 1600 psig pops to the spec'ed 1950 psig? And, yes I tested on my electronic pop tester. On a related note, I can't say I noticed a difference from changing the injector timing (start of delivery) from spec 24 deg BTDC to 27 deg, in both 300D's.
Spray pattern is very important since small droplets are critical to combustion and a uniform mixture, but the non-turbo 1600 psig injectors give about as good a pattern as the 1950 psig turbo injectors, as they should. Most of the time while driving the turbo is not adding significant boost. Does anybody know why the designers made the turbo injectors pop higher?