Howard Coleman

iTrader: (6)

as i understand, Apexi says that the injector drivers should see no more than 2 amps.

my 1600, 1680s (take your pick) have a R of 2.8 ohms.

so 12 volts divided by the 2.8 plus whatever resistor you choose, say 4 ohms, ends up at 1.76 amps.

my question relates to the "volts" in the equation. my DL says i generally have 14.4 volts.

which V number should i use?

currently i have 10 ohm resistors in the system and have always had to jack up the Ms a ton for the 400 rpm segment where my primary and secondary injectors mesh.

i realize there are other factors but would like to get the volt number proper so i can resize my resistors.

thanks,

howard

cewrx7r1

iTrader: (2)

My Bosch 1600 kit came from the RX7 store with 3 ohm resistors.
I contacted them about this as I thought they were too low.
They said NO PROBLEM with them.

2.8 + 3 = 5.8 ohms.

14.1 / 5.8 = 2.4 amps
12 / 5.8 = 2.1 amps

Haven't had any problems with them and they have been in the car for two years.
If the car was a road race car, then I would run a bigger resitor due to the turn on time being very high. The higher value resistor should only affect lag by increasing it.

Who really knows the answer?

My dataloging shows my transition from 550 to 550+1600 to go richer. That is when I started playing with the transition (ms) and (%). I had posted on this and it is in my tuning notes.

I run 30% and .100 ms.

Wargasm

I don't think there is an easily-proven answer.

The main thing is that as far as I know, the factory secondaries are saturated type injectors. This means that the ECU hits them with "full" power (calculated with your V=IR formula) for the whole pulse.

Aftermarket low impedance are peak and hold type. These work by sending a zap to open them fast and then it scales back a little for the rest of the pulse. Because the PFC doesn't have the right driver circuit for this, it just hits them with full power the whole time as far as I know... therefore, the primary concern in my mind is to avoid overheating them/burning the circuit out.

*edit* So the upshot is that if you put bigger resistors in, you protect the injectors and the driver circuit a little more, but you may find they become sluggish due to no "peak" for the peak and hold *end edit*

I use 10 Ohm 20 Watt resistors on my car and they work great for me.

I'd focus more on preventing burn-out then I would on trying to make them exactly like the factory ones (which they'll never be)

Wargasm

To expand a bit more...

Your stock system is somewhere around 1 amp.

14 volts / 14 ohms = about 1 amp.

Your aftermarket peak and holds are looking for either...

4 amps to open, followed by 1 amp hold
or
2 amps to open, followed by 0.5 amp hold

Putting a 3 Ohm injector + a 10 Ohm external resistor nicely approximates the factory setup from the point of view of the computer (therefore it is protected), but, your new low-impedance injector is kinda not feeling the "peak love" that it wants as a peak-and-hold. Using a smaller resistor only solves half the problem. Sure, you get more amps to pop the injector open, but there is no back-off. It just holds it at that higher value.

Will it burn your injector or driver circuit out? Maybe not since most of the time, for a street car, your on-time isn't that high for secondaries. This might temporarily heat the stuff up a bit, but it will cool when you drop the duty%. As long as you don't slam it with way too much it can probably tolerate a bit of juice. Is it cool with Apexi to hit 2 amps for a few seconds, or can it drive 2 amps all day long? I dunno. I don't want to try to find out. If someone opened their PFC up, they might (MIGHT) be able to figure out what components are on the board and look up the specs on the 'net and figure out more info. Since some folks circuit race, they will really stress the secondaries more than your typical street machine that spends 99% of the time under 4k rpm.

Reference: http://www.twminduction.com/EFI/EFIInjectors.html

Wargasm

One more thing and I swear I'll shut up....

Make sure the resistors you buy can dissipate the proper amount of power.

P = IV

for my setup that is

P = (1)(14) *approx*
P = 14
This is why I'm using 10 Ohm, 20 Watt resistors. If you burn out your resistor, the circuit will fail open and that's a bad thing.

Howard Coleman

iTrader: (6)

thank you, both, for you help.

hc

Howard Coleman

iTrader: (6)

looking at the numbers...


given:

14.0 volts from my logs

resistor--------amps
10 ohm--------1.09 amps
9----------------1.18
8----------------1.29
7----------------1.42
6----------------1.59
5----------------1.79
4----------------2.05
3----------------2.41

since i run 10 ohm R that may explain why i have been unable to tune out a 50% Ms bulge in my base fuel map as my secondaries come on. i have adjusted most of the variables all over the place and have never made a dent in my fuel bulge. while my AFRs are steady i have never liked the looks of my base fuel line charts.

currently i have my injectors set at the RC flow numbers 888/1658. i use 64.5 for the primaries and the popular .04 and .14 for the lag. primary/secondary transition is 40%. i have tried 30 and they still seem to come on at 48% w either setting... and my secondary transition is at .7 Ms. i have been all over the block w most of these settings and had sort of resigned myself to the initial secondary bulge setting.

perhaps w my 10 ohm resistors the secondaries just aren't getting the initial blast and i am having to make up for it by raising the Ms a bunch. after the 800 rpm transition they gome back to the trendline...

based on all of the above posts i will probably see if i can find some 4 ohm resistors.

howard coleman

Jodeny

iTrader: (3)

Howard,
Talk to Ralph at groundzero. He doesn't use any resistors. I believe he stated that they slow down the reaction time of the injector but don't quote me on that...
John

cewrx7r1

iTrader: (2)

Howard,

I was looking for an old post of mine and came across this one which was posted
after I received my Bosch 1600 injectors from the RX7 Store.

"The Bosch injectors are 5.1 ohm."

I had measured mine with my digital multimeter.
Did you actually measure yours at 2.8ohms?

5.1 + 3 = 8.1.

14.1 / 8.1 = 1.7 amps thus very safe!