Injector Impedance

[Fish]

I used these when I did my 1600cc upgrade.

You can get bigger non-metal cased, but I thought they looked better.

Fish

[kbareham]

Diabolical1-

It\'s a while since I studied this, but from memory:

High impedance injectors (around 16 ohms) are easy to drive, since even fed directly across the battery voltage, the current is not too high. The disadvantage is that the low current causes extra delay in opening the injector (lag) especially at low battery voltages.

Low impedance injectors (around 4 ohms) would draw excessive current if fed directly from the battery voltage. If used with an ECU having appropriate peak and hold injector drivers, the ECU can allow the injector to draw a high initial current, thus opening quickly, and then regulate the current to a sustainable hold value for the rest of the pulse. When done correctly, this maximises the open period for a given pulse width, and reduces sensitivity to battery voltage.

Using low impedance injectors with resistors of course does not give the fast opening times that might otherwise be available. However, some manufacturers have used this method in the past.

There were at some time injector driver boxes that you could drive with your ECU to overcome this. I haven\'t looked around for a few years, but they may still be available if you are really interested. I think that I would try the resistors first.

Keith

[diabolical1]

thanks, kbareham! things make more sense to me now.

[crispyj]

I have spoken too Re-Worx about the 1600cc injectors and he has told me that they have fitted lots off these without resistors and they have not had any issues with the PFC.

So i dont know if to fit the 10 Ohm resistors or not.  If I dont fit them and it melts the ecu will the car run lean and melt a tip or  if I do fit them will it make setup for the guys at Re-worx more difficult as a resistor may slow the injector opening times.   :rolleyes:

[Prof]

I would find out what the power FC can tolerate current wise.  You might find you can get away without resistors, because for the most part the duty cycle on the secondaries is going to be low.

For example, if you had 4 ohm injectors, then across 12 volts they would draw 3 Amps.  If the duty cycle is only 10%, then the \'effective\' current drawn (for the purpose of working out heat dissipation and so on) is only 0.3 Amps.

The main things to watch for are the maximum allowable current through the injector, and the maximum current that the ecu can sink (injector current is drawn to ground through the transistors in the ECU).  Provided you don\'t go outside these limits, you should be ok.  

I\'m guessing that you wont be sitting at WOT for long extended periods  :Nono!

Best off asking Re-Worx what they think.

[Fish]

Some of the threads on the RX7Club forums, people have had issues with the PFC and not running resistors on the 1600\'s.

Fish

[Mazdarotaryparts]

We have fitted quite a few of these kits with never a problem as well, but can only comment on carts with a PFC.

Hope this helps

[Mazdarotaryparts]

We have fitted quite a few of these kits without resistors with never a problem as well, but can only comment on cars with a PFC.

Hope this helps

[crispyj]

Re-worx said it would be OK without resistors.  

Fish just for reference can you tell me the size of the resistors you have fitted on your 1600 injectors and who did the tune/setup.

Thanks crispyj

[Fish]

I think they are the 10W 10 Ohm type. I got the details from a thread on the RX7Club forums.

Clicky to the KGParts fitting site

Fish