well i was looking for some low impedence injectors . looking threw the forum i noticed some 1 selling 780cc gm delphi injectors low imp . so i did some reasearch and seen how much cheaper they are . my question is are they a strait drop in? i dont care about the clips i will get some to fit it . i am gonna be using rtek 1.8 4x720 injectors . these are 780s . i rather buy oem style injectors over the rc

these are the ones i want to purchace.
http://www.racetronix.biz/itemdesc.a...113742&eq=&Tp=

they also have these
seimens ones 760cc .
http://www.racetronix.biz/itemdesc.a...I11445&eq=&Tp=

 

yeah i am interested too. the 720cc injectors are hard to find, the greddy ones rx-7 club.com sels are expensive. like $590 for all 4

 

yea these are alot cheaper i feel like they would last longer

 

The real question is if they physically fit exactly the same way as the stock injectors. You need to find detailed dimensions of the injector and compare that to the stock component. You can adjust some dimensions by using different grommet thicknesses, get it machined down to a certain size, use spacers on the fuel rails, etc.

 

I have the seimens 750cc injectors (3145).

They have a layer of plastic that extends up almost the entire neck as opposed to the stock injectors that have a long thin metal neck and uses grommets to keep them from sliding too far into the fuel rail.

This makes no difference for the secondary injectors, as the lower mounting hole is deep enough to accommodate the difference in mounting position. However the primary injectors need to have that plastic trimmed (turned if you want to be fancy) down so that it can fit inside of the hole in the fuel rail. It took about 5 min w/ a dremmel to do both of them.

As an alternative you could use spacers on the fuel rail mounting point to make up for the difference, but room under the TII UIM is kinda tight, so I chose not to go that route.

Edit: What does the rtek have to do with this thread?

 

just want to make sure they work with the rtek fine . so basically just a little triming they fit good? and if not were can i find the right spacers for them

 

The rtek 1.8 is non-adjustable and its looking for 720's. Anything larger and it runs rich, anything smaller and it runs lean.

You need to consider that when you purchase injectors they are rated at a specific psi, 43.5 for example in the case of the Seimens 3145. If you run them at a lower psi they will flow less (I believe 40 psi is actually around 722cc) and if you run them at a higher psi they will flow more. IF you are running stock fuel pressure (36-38 psi) then you will probably flow less than 720cc on "750cc injectors"

Injector-Rehab.com has an excellent flow converter and fuel requirement calculator, you should check them out.

As far as fitment, yeah its easy. I actually used spacers on the secondaries before I figured out they would slide further into the mounting holes. I used a ball bearing to space the rail up about 5-6mm. It was a tight fit w/ the s4 UIM there was only about 2-3mm clearance once tightened down. The S5 UIM would have plenty of room.

 

im gonna be doing a walbro thats about it . so i shouldnt buy these for my rtek 1.8? and i dont mind running richer . as LONG as i dont run lean EVER idc

 

also, using low-imp injectors with resistors can reduce their capacity by 15%. doesnt hurt to go a little bigger. rtek 1.8 takes out the extra fuel anyway

 

With a walbro you'll be fine, because it will overrun the stock fpr and increase the fuel pressure at least 2-3 psi.

Are you referring to the stock resistor pack or splicing in resistors on a system expecting High imp injectors?

 

i hope it dont affect my idle thats all . cause i am gonna using my ac and i have a sound system . getting a upgraded alternator. lets see how it goes

 

nothing a bac and variable resistor can't compensate for

 

At idle and low-load, you'll notice more of a difference from the walbro jacking up fuel pressure than from the slightly larger primary injectors. You should be able to correct the idle by cranking the variable resistor over to "Lean", but low-load and high-load mixtures will not be adjustable.

 

let us know if this works, i plan on running the same setup

 

The Rtek 2.1 is worth getting for the cranking fuel map adjustment alone. Not to mention the error code checking and timing control, but the 1.8 will do in a pinch.

 

rtek 1.x series are nothing but fail and asking for trouble

ive never experience any rise in fuel pressure due to walbro 255.

stock resistors are 6.2 ohm, but higher resistance definitely will make it worse. I think the injector drivers can handle up to 3A, with means a minimum of 4.5 ohm resistors inline. any resistor inline will cause shortened injector pulsewidths

 

what varible resitor we talking about

 

Check the FSM. The VR is next to the MAP sensor on S4s.

What fuel pressure have you measured? Stock FPR, right?

I tested a walbro and an FD fuel pump with the stock FPR awhile back, and this was the result:

12 psi difference at idle, 7 psi difference at 0 manifold pressure and 3 psi difference with 10 psi applied to the FPR.

 

^^^ exactly.

When I first got my car it was stock except for a walbro 255. It used to smoke at start up, idle low/rich, and was often hard to start.

After I switched to an fd pump all these problems disappeared. The stock fpr is not up to the task when paired w/ a high output fuel pump.

 

Here's my D/R 3472's, picked them up from a bunch that apparently doesnt make them anymore. From what I have found on a unmodded 3472 the flow rate is 775cc @ 43.5 psi, length is 3" or 74mm, top an bottom o-ring 14.5mm. Oh, an stock clips should fit.

 

so that resitor box is adjustable??

 

Can anybody post what gm cars came with this injectors.