I didn't realize that S4's were square and S5's were oval. I go to put the new injectors in and they are square, I have an S5...****... I'm getting tuned on saturday, can I put my walbro 255 in still or is that pretty much worthless on the stock injectors.

 

What size / condition injectors? I may be interested in buying... rich

 

I have a Walbro 255 on stock injectors for when I'm ready to switch to 720's +... just put it in and get it done ok, actually it came on the car like that... but that's good.

 

Definately still put the walbro pump in. The 720s will fit in no problem, all you need to do is buy a pair of bosch style injector connectors. A local auto parts store may carry it. Just cut off the stock connectors and solder in the new ones. Simple as that. Dont forget to solder in resistors at the ECU for the 720s (assuming they are low impedence like almost everything other big injector).

 

there are two wires going to each injector, which wire do I splice the resistors into (1 resistor for each injector)?

 

Why hack up your harness over the want of two injectors?
And he also has to buy the resistors + wire + connectors! Just buy some s5 injectors....That's definitely the simple way. ~rich

 

Yea I'm not going to rush it, I'll just wait until I can get it tuned again to get the right 720's.

 

uhhh do you know WTF you are talking about?? S5's have oval injectors with oval connectors. they do not sell any aftermarket injectors with that connector. You HAVE TO change to a bosch style injector unless you dremel out the stock connectors. He already has s5 injectors in his car. he wants to put in his 720s. When you buy the connectors they come with wire lengths already attached NOOB! resistors costs $1.xx at radio shack for 2. The fact that you need to solder in resistors already means you need to either cut the harness or at least unsheath it. You can solder in the resistors on either wire, it doesnt matter.

Dont talk if you dont know.

 

Wrong... I have couple 780cc oval connector injectors. You can get them but they are EXTREMELY hard to find. Mine are Venom injectors, got them off a forum member who got them from a vendor.

 

So you are absolutely certain he cannot find larger, saturation style, high-impedance, oval type connector, fuel injectors that will fit? Not at all? I'm fully prepared to apologize for misleading him if wrong...

But I do apologize for failing to mention he'll also have to change his ECU to a peak and hold (pre '87.5) to accomodate these larger, different injectors and since he'll now have a peak and hold style ECU the primary injectors which are saturation style, will also have to be changed out to match.... $$$.$$ ~rich

 

I'm pretty sure that:

peak and hold + resisters = saturation

The only time you can't convert is when the ECU is designed for peak and hold without resistors.

In other words: You can't make a saturation injector look like a peak and hold but you can make a peak and hold look like a saturation by adding a resister.

ed

 

Sorry but an S4 ecu will not work with an S5. what about electronic OMP? Do a search for peak hold vs. saturation type injectors about how they operate. it'll explain why most high cc injectors are peak hold and not saturation.

 

No - doesn't work that way. The PaH uses a higher opening current to open them and a lower current to keep them open. The saturation uses a broad, low current during the injector pulse. You may be able to physically make it work but it will negate the benefit of having the peak and hold circuit.

You are right about the ECU - don't have my thinking cap on. The VDI will not work either, etc... The point I was making is it's not a good idea to modify when you can buy in this case. ~rich