FC Injectors - Part 2

[grinder]

how do you put resistors on injectors ..

you idea idea of how USED they are ?

*** edit ***

me again

how do you know they are low rated ones ??

im not too keen on hacking the wires to fit resistors

why is nothing straight forward on a FC eh ??

read : http://www.rx7club.com/showthread.php?t=121793&highlight=720+resistor

[Prof]

To fit the resistors:

1. You need to cut one of the wires that goes to the injector plug.  

2. You then need to buy a 10 Ohm - 20/30 Watt resistor (the wirewound ones that come in their own heatsink are best - look cool too, as they are gold in colour).  

3. Place a bit of heatshrink tubing over each end of the wire you cut - and move it along the wire quite a bit (keep it cool when soldering  :yes )

4.  Pare back the insulation on each wire end.

5.  Solder the resistor in place.  

6.  Push back the heat shrink over the fresh solder joins and wave a hair dryer over it.

It doesn\'t matter which lead you cut, as the resistor will be in series either way, however if someone is measuring voltages on the car, they will get the same readings as Hi-Impedance injectors if you put the resistor on the positive supply line (the ecu\'s have power transistors that ground the injector which fires it).

As to how used they are  - I don\'t know.  I got this off ebay - they look pretty clean, but are minus the O-rings on the top.  They are in an injector mounting bung, so there are just three hex bolts to release them.  They are top mount and should fit the standard fuel rails.  They are labelled as DENSO, and have a blue rectangular connector.  Not sure what connector the S5 FC has.

I decided to go with the 800\'s, and possibly up the fuel rail pressure just a smidge  

I\'ll keep the primaries as 550, as it seems there is much better control for idle and low rpm.  There is also spare capacity on these, so there should be about another 500cc worth of fuel on each rotor to be had with the larger secondaries.  (An overall fuel increase of 66% based on 85% PWM).

That\'s gotter be enough to see 300BHP at the fly, with an increase in boost on the stock turbo (12-14 psi max) !  :yes

Now I just need to find/make a boost controller and something to map the extra fuel - and of course cooling ! :Thumbs-up

[Prof]

Just read through that other thread regarding injectors - god they make it complicated.

Here\'s a quickish lesson on solenoids / injectors.

Basically these devices use a current to actuate them.  So if you apply a voltage across the connector, it will cause a current to flow.

For clarity\'s sake let\'s keep the figures simple, so the maths is easier.

A High Impedance injector will be about 12 Ohms.  Assuming 12V supply, you will get a current flow of 1 Amp.

With a Low Impedance Injector of 2 Ohms, and 12V Supply, you will get about 6A, followed by a melting plastic smell, and a small fire as the injectors catch fire !

So the 10 Ohm resistor in series adds resistance restoring the 1 Amp current flow.

As it happens, the S4 cars had a pack of resistors for just such a purpose, so these can be used if you can find them.  Otherwise anything in the region of about 8-10 Ohms should work.  Power resistors come in strange values (2.7, 3.3, 3.6, 4.7, 5.6, 6.8, 8.2, 10) - Dont be tempted to go any lower than the 8.2 Ohms for the reasons above.

Hope that helps ?

[grinder]

matey - i love you electonics 101 lessons

they make sense

IF i get your 720\'s i can control them with the SAFC ( once its fitted ) - so thats not a prob from my end

Stu