dropping resistors

[magic formula]

I know this topic has been covered before, but...
I have the 420cc benz injectors, which are low impedance, with an 88t ecu (my car is an 87t) which i believe, if i have the terminology correct is a saturated ecu, The PO had been using resistors with the injectors. He had a fairly decent tune going. When i got the nistune stuff, due to reading in multiple places that it didnt make any difference, i decided to leave them out. I recently hooked up the PO's tune without the resistors, and the car was running SUPER pig rich. So there is definitely a huge difference in the amount of fuel delivered when resistors are used. I suppose using nistune one could create a tune to make it work either way. But seeing that there is such a stark difference in the amount of fuel delivered, one would have to think that one way or the other is the optimum way to go.

Other random thoughts that may or may not be related...

When using the resize injectors operation, going from stock 260cc and a k value of 607 to 420cc gives a k of 375. But my tuning experience so far has told me that a k value of 250-260 is best. This scenario is with no resistors. I haven't tried it yet, but i bet that if i put in the resistors, i will be much closer the the "suggested" k value of 375. I suppose my point here is that using the resistors should make the tuning a bit easier, as the resize injector, ttmin, max and other stuff that is automatically done with this function should be closer on the mark. idk.

Any thoughts on this subject are appreciated, as i am still trying to wrap my head around this issue, and tuning in general.

Thanks,
Brian

[Matt]

the resize injector calculation is purely based off theoretics. if X injectors are resized to Y injectors must reduce the amount of flow by X/Y CCs

then given that increased k adjustment, allow for a greater load range and adjust accordingly (also increase your max pulsewidth allowed)

then take into account the opening/closing time (latency) @ 14v as well as latency changes at other battery voltages. all the result of characteristics of different injector types and sizes

when you compare injection types saturated vs peak hold then the characteristics of injection change but I dont know the exact effects of this throughout the rpm range

definately having an high impedance mismatch can be the difference between overloading your injector drivers and perhaps opening/closing them a lot quicker than usual (latency being lower would be lower most likely). the easy answer here is to match the original impedance and drop the resistance using inline resistors

regarding low impedance mismatch not driving them hard enough may make them act a bit lazier and need k + latency adjustments to make up for this

I'm sure if you google this stuff there is a lot of discussion regarding this, not only for Nissans but other vehicles also which may provide some more definitive information. I'd be interested to see others opinions here also

[PL]

I tend to play with the later model stuff but FWIW Nissan use around 6 ohms. This value does seem to do the trick - if you can find them.

Theoretically you need to dissipate around 17W worst case (injectors running at 100%) so they're gonna be pretty chunky. Looking at the size of the dropping resistor packs that Nissan use it would appear that they've got some sizeable resistors in there.

I'd say you'd want 20 or 25W resistors. You may get away with less if it's just a street car and you keep an eye on the temperature.

PL