I'm considering the purchase of a GZ/Xcessive LIM with 4 sec injector positions.

Considering the fast I have quite a lot of part laying around, I could do a sec fuel setup with 4 850 cc OEM injectors (and 2x 550cc prim) by splicing the OEM wiring

Keeping in mind that the OEM injector system is high impedance (12-16Ohms) I need to verify if the OEm wiring and more importantly, the APEXI PFC unit will be able to cope with that.

So... Did anyone try/verify this yet? Can the PFC injector driver handle double the impedance?


If not, another option could be to add 2 very fast reacting relays that only use the original injector wiring as a 'signal' to make the relays work.

I know there is the low impedance 1600cc injector option or the FJO, just looking at some options

Any (usefull) input would be highly appreciated.

 

There is a section in the FC edit documentation (Datalogit software) that covers this exactly. The short answer is yes, and I'm pretty sure you don't even need resistors. you will have to change your secondary injector size and play around with injector transition settings.

Don't even bother, your very fast acting relays are probably way slower than a fuel injector, especially a low impedence one. Low impedence injectors are designed to have very few solenoid coil windings in order to improve response. This is discussed in the 2nd generation (FC) training manual.

 

thx,

so what you are saying is it is not possible to run 4 850cc (OEM injectors) in the sec positions?

But rather a combo of 2 850cc's and 2 additional ones with a lower flow rate? If that is what you are sugesting, I don't see the problem with 4 850cc's either as it all comes down to the Ohms the injectors are rated at.

If you mean 4850cc's in the sec rail are possible, that would be great.


I'm planning to use OEm injectors, so they are all high impedance. A fast reacting relay would be something like a MOSFET type relay

 

I'm not saying that. Do you have the Datalogit instructions? There is a section in there that talks about wiring up a pair of series 5 FC top feed injectors which are very similar impedence to the FD 850 CC's. But the bigger question to me is, where are you going to get a side feed rail that will work in the GZ LIM?

 

you are right I only though of that after I posted the thread. So I would havet o switch to top feed injectors for that setup (like Sard's). my bad there

In other words, the Apexi internal injector driver is up to the task of extra 'load'

 

according to the makers of the datalogit, the injector drivers can handle up to 3 watts. They explain the method for calculating how much wattage the drivers are seeing. I have elaborated on this further.

V=I * R (Ohm's law. max battery voltage the injector will see = current across injector multiplied by resistance across injector. Solve for current)

P=I^2* R (Power drain on the injector driver = current across injector from the calculation above ^ multiplied by the resistance of the driver itself, which is .25 ohms according the FC Datalogit)

You need to do the power calculation for each of the 4 injectors and then add it all up to see if it's under 3 watts. I explained it further in a couple other threads, doing a full calculation with real numbers. It's in at least two threads in the 3rd gen section and one in the PFC section.

 

nice exactly what i was looking for thanks for the info...... 3w


z

 

see https://www.rx7club.com/power-fc-forum-47/power-fc-injector-resistors-849993/ for a full example of how to do the calculation

for the V=IR calculation, you have to add all the resistances together on an individual injector's circuit. So if you are trying to run 6 injectors, for a front secondary calculation you would have the first injector's resistance added to the additional injector's resistance. Then add any resistor on top of that.

so total resistance is

Front secondary injector 1 impedence + Front secondary injector 2 impedence + any resistor .

on a primary circuit, you would have

front primary injector impedence + any resistor

 

I talked to WGT performance in Uk about the topic and they seem to have tried this set up several times with good results. The PFC ECU seems to be able to cope with 2 additional 850cc (OEM) injectors

 

I would run a Peak and Hold injector driver just to be on the safe side, it keeps the powerfc happy.