fuel injector question

[sLoWnStEaDy]

OK time has come to buy some injectors, i have to chose between two sets. both are the same price. they are going on a 3.4L DOHC pushin like 8-10 pounds of boost daily. when i get my new rods and pistons, i will be crankin the boost up. so which should i get. both are made for a mustang, but will work for my application.

Ford Motorsport 42# injectors, green top

MSD 50# injectors, PN 2013


usually id jus say bigger is better, but thats not always the case, so i figured id see what you'all have to say about it.

[TbTalon94]

What are you going to be tuning the car with? How much power are you going for?

Once again do not select things in referance to boost. Please Please stop using this concept. It annoys me very much.

-Trevor

[sLoWnStEaDy]

ill only have an SAFCII, ill be paying someone to tune.

for now im going for 300-350 RWHP at 10psi.

sorry trevor, please excuse my ignorance. i want to understand this shit, but im more of a look and listen to learn, not so much read a bunch of stuff that goes completely over my head and try to get some useful info out of it. sadly, the only thing i am using to reference parts is by looking at what other people have used, finding out what there weak points are/where then trying to kinda get the best from each and put it all together. ive read tons and tons of info, but i dont really remember/comprehend much of it. i need to hang out with people who actually know what they're talking about and have actually built systems and such.

[logans dad]

Will my old stock injectors work, I dont know what your car is but heard they work great in some Honda's.

[krustindumm]

What is your stock injector size and HP?

[sLoWnStEaDy]

i believe the stock flow rate is like 22.5 lb/hr
and the engine is rated @ 220 BHP

[TbTalon94]

What kind of injectors does your car run? High/Low impendence? Peak and hold? Dsm Injectors might work but of course you will need 6 of them. Whatever you car has you will need to wire in resistors if you were to use the other type of injector.

[sLoWnStEaDy]

WOW? i really have no frikkin idea, ill tell you the little bit i do know.

the short block is from a 1993 lumina Z34 (3.4L TDC, VIN X)
the heads are P&Pd from the same car
cam carriers are newer, better versions from 94-95 monte carlo (same engine)
using 94-95 (monte) ECM and wiring harness

so i guess they are whatever the 91-95 lumina Z34, 94-95 mont, 91-93 cutlass, 91-93 GTP etc. i do know that most people use 42# mustang injectors without any resistors, but wether they are high/low im not sure.

WHERE THE HELL CAN I FIND THIS STUFF OUT AT????

[krustindumm]

i'm pretty sure you can use the DSM's. Just need to measure the impedance of the stock injectors to find out if they are saturated (high) or peak & hold (low) type to know if you need resistors.

The reason i think you can use the DSM's, is i think mustang injectors fit Honda's, and so do DSM injectors.

I'd stay below 45lb/hr if you are only using an SAFC. You may run out of correction factor with anything larger (based off your stock injector size).

[Guch]

Have you actually heard of people running a resistor in series with a peak and hold injector to make it compatable with a saturated type ECM?

FYI: your factory ECU should be saturated - you need High impedance injectors which the 42# ford SVO injectors are compatable.

[krustindumm]

Have you actually heard of people running a resistor in series with a peak and hold injector to make it compatable with a saturated type ECM?


:werd: 91+ Honda and n/a DSM people have been doing this for years to run turbo DSM injectors.

Grab a resistor pack from any turbo DSM or pre~92 MPFI Honda.

[Ricky]

Do you plan on having an intercooler? if so were is it going...?

[sLoWnStEaDy]

yeah i do, check out my original build thread below. intercooler talk is half way down page 5

sadly the car is pretty much just how it was back then. only difference is the heads are finaly done, and i repainted all the blue stuff with a "metal flake" blue i found at Autozone!! pretty much exact match to my metallic blue paint on the fiero.

http://www.crunderground.com/viewtopic. ... p&&start=0 (http://www.crunderground.com/viewtopic.php?t=6712&postdays=0&postorder=asc&highlight=fiero+swap&&start=0)

but yeah anyways, i guess i can update that a lill now.

[Guch]

:werd: 91+ Honda and n/a DSM people have been doing this for years to run turbo DSM injectors.

Grab a resistor pack from any turbo DSM or pre~92 MPFI Honda.

What do the Ohm out at? So they run a resistor in series with the injector dropping voltage to the injector? I'm not being a dick but it doesn't make sense unless they have really strange ass logic.

[krustindumm]

IIRC, 10 ohm resistors. Some people use 10ohm/10watt ceramic resistors in place of the resistor packs.

Drops the voltage to the injector and limits current, that's all.

[DJ0820]

http://www.hondata.com/techlowohminjectors.html

[Guch]

So they did this on purpose. Please fill me in on this madness. I don't get it .I understand the theory and why they did it(cheap). Lets say you have sequential injection with a low impeadance injector with a 7 ohm resistor with total current draw of 1 amp.
So the resistor is dropping 7 volts, the injector dropping the other 5V. I guess I'm not a fan of lazy injectors or am I missing something that you have read about.

[sLoWnStEaDy]

OK, got 6 450cc injectors. they are peak and hold low impedence. and my system is saturated high impedence.

RESISTORS...

Where (can i get them)

Which (size do i need)

How (the hell do i add them the the wiring?)

[krustindumm]

radioshack
10 ohm / 10 watt
inline (series) with whichever side you want to.

[sLoWnStEaDy]

well, finaly gettin to the point where ill need to know for sure...

i was told:
resistors with peak/hold injectors on saturated drivers is a bad idea.

It's a cheap-ass hack job.

The problem with running resistors with p/h injector and saturated drivers is that you give up the BEST feature of p/h injectors... their FAST opening time. They slow WAY down and act like really slow saturated injectors if you run them with saturated drivers. They also have the potential to run at higher than ideal temps because they'll be getting more average current than they would when used properly.

true? once again only ask because i have the 450CC dsm injectors and the 10/10 resistors. If this is true i will have to get some 42#ers which'll be like $300+ or some L67 36#ers which'll be like $100, but i would like to go a little bigger than 36#

[krustindumm]

The problem with running resistors with p/h injector and saturated drivers is that you give up the BEST feature of p/h injectors... their FAST opening time. They slow WAY down and act like really slow saturated injectors if you run them with saturated drivers. They also have the potential to run at higher than ideal temps because they'll be getting more average current than they would when used properly.

It might be a cheap hack job, but it works. Honda people have been doing it for over a decade.

The fast opening time is still there, because the smaller coil on the lower impedance injector has lower inductance. Inductance resists changes in current, so a high impedance injector (larger coill=more inductance) will resist current flow more at the instant the injector is powered. Since the other resists less, current will flow sooner, and it will open sooner.

As for the higher current causing heating problems, I doubt it. Run them at acceptable duty cycles and it should be fine, again, no Honda's have had problems with this hack, even at and near 100% duty cycle.

[SLVR7]

[quote="krustindumm";p="102538":c89ed]
:werd: 91+ Honda and n/a DSM people have been doing this for years to run turbo DSM injectors.

Grab a resistor pack from any turbo DSM or pre~92 MPFI Honda.

What do the Ohm out at? So they run a resistor in series with the injector dropping voltage to the injector? I'm not being a dick but it doesn't make sense unless they have really strange a$$ logic.
[/quote:c89ed]

Running the resistors drops the amperage, so you don't burn out the injector driver. I run resistors with my set up for the same reason. Mouser electronics is the cheapest place to get good military grade ceramic resistors with heat sinks built in. For picking which resistor you need, measure the ohms of your original injector, then pick a resistor that makes your new injector equal the original.

[krustindumm]

it also drops the voltage to the injector.