i am using hight inpedence secondary stock 850cc fd injectors and venom 550 low inpedance primaries i am using a stock ecu in my 87 rx7 and i need to find out if i need to put in resistors for the stock fd injectors

 

bump

 

you just answered your own question: the fd injectors are high impedence thus no resistor.

 

what happens if i run the resistors with them?

 

^ They might not open, or open very slowly and not work well. Basically, just don't run a high impedance injector with a resistor if you want your car to work well (or work at all).

Seek to understand the basic relationship between resistors and injectors first, so that you can make the right choices for your car...

High impedance injector = no resistor required. Don't run a resistor with a high impedance injector.

It is only low impedance injectors that may require you to run resistors (and only if they are replacements for high impedance injectors). If you have factory resistors already (to go along with factory-installed low impedance injectors; I think my 88 Turbo II had factory resistors, IIRC), you could just eliminate the resistor from the circuit.

-Max

 

what about mixing/adding low impedence injectors to high impedence ie adding an extra low impedence in line with the stock high impedence?

 

You shouldn't add a low impedance injector in parallel with a high impedance injector, because the resulting impedance would be less than the low impedance injector on it's own. The risk here is that it would burn out the injector driver circuit in the ECU (too much current).

Idk if this would work or not, but you might be able to use a low impedance injector + resistor (low imp inj + resistor in series) wired in parallel with the existing high impedance injector. That would increase the current somewhat, and risks burning out the injector driver circuit in the ECU, but it might work.

I also don't know if this would work, but another possibility would be to use the low impedance injector wired in series with the high impedance injector. The high impedance injector would sort of be acting like a resistor in this scenario.

However, the safest option would be to simply get a larger high impedance injector, or have your existing injector enlarged (which is somewhat controversial, but has worked fine for many). Or, if you just need a little extra fuel flow and have a good fuel pump and a programmable ECU (to adjust the low load fuel flow back down), you could run higher fuel pressure. Or get an additional injector controller box and use that to control the additional injectors.

-Max