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But why does this make such a difference? What happens if you use a high impedance?
This is how I understand it (if I'm wrong, then someone please correct me):
If you use a low impedance injector on a 951 (for example) then the injector drivers will send too much power to them and they won't use it all. That stored energy will stay in the injector driver circuit in the DME and could potentially damage it. This is usually only an issue if you are WOT most of the time (like a track car) and doesn't make much heat if you're just cruising.
**DISCLAIMER: The above is MY understanding. If I'm wrong, lemme know!**
Darwin, I think you're basically correct. My understanding is somewhat simpler - the injector circuit was designed by Porsche for injectors of a certain impedance. Putting injectors with the wrong impedance in there will throw voltages all over the circuit out of whack and likely break something. You can use ballast resistors to get the total impedance to the right number, but you really want to do that if you're going to change injectors
Darwin, I think you're basically correct. My understanding is somewhat simpler - the injector circuit was designed by Porsche for injectors of a certain impedance. Putting injectors with the wrong impedance in there will throw voltages all over the circuit out of whack and likely break something. You can use ballast resistors to get the total impedance to the right number, but you really want to do that if you're going to change injectors
I added ballast resistors for my low impedance Siemens 55lb injectors. It was really easy to do.
the ford supercoupe/porsche 951 injector (same part) is a low-impedance, 36 lb/hr injector. it will plug into your manifold and into your harness.
They are not the same part but seem to flow very close to each other. The turbo are green top (4.5 ohm) Bosch and the supercoupe are brown top (2.8ohm) Bosch.
The difference is that a low impedance is generally around 2.2-2.8 ohm and is peak hold design
the high are around 16 ohm and are saturated design.
they are not interchangable. However you can use low impedance in the 951 (4.5 oddball) for street use from what I hear they overheat the drivers in a race app and need resistors. If you try to run a high on a low driver setup it will run very lean.