Mongo

Where is the solid mount mentioned above? I looking at PET now.

SeanR

That's......interesting.

Hilton

I have that style of injector handy too - they were the first type of design III I bought.

After fitting them in a fuel rail off the car, and then subsequently measuring them, I was not willing to install this injector body style on the vehicle.

The issue is that unlike the properly grooved injectors, these provide a rounded surface which can force the retainer clip apart over time, so whilst it would apparently hold in place, with a small amount of pressure it can push (pull in the case of my testing) out of the fuel rail. The rounded resting surface issue was, IIRC, compounded by the fact that the injector "neck" is narrower than on the correctly grooved ones, which allows the clip to **** over on one edge, onto the curved surface.

The correctly grooved clips provide a completely flat surface to seat the retaining clip on with no play, which isn't prone to this problem. Thats also why I started the other thread to document finding the design III injectors with the correct grooves.

Hilton

Mongo, for Ken's chips, I'd just buy some design II injectors. Same physical body style as the stock injectors, but will a disc-style with 4 holes like the design III.

I've got a set of the Ford Racing 24lb ones I picked up used for about $60 on ebay, which I then cleaned myself - they're not that hard to find.

0 280 150 947, aka 0280150947, aka F1TE-D5A (Ford factory injectors for Ford Mustang Cobras 4.6 L. from 1995 - 1998), also sold as Ford Racing M-9593-A302

They're 4-hole, fit perfectly on stock rails, and are also well documented (injector opening times etc. all easily found online).

To use them, you can either just buy the correct top and bottom o-rings from a 928 supplier (I bought the correct Bosch lower o-rings from John Speake - rather than aftermarket lower o-rings from other sources), or buy the correct rebuild kit from Porsche (which includes pintle caps, plastic spacer, and the correct o-rings).

edit for Porken: In my opinion the best injector solution for non-stock use on S4's is the 30lb one.. Ford Racing m-9593-bb302 aka 0 280 155 759 aka 9454556 (volvo p/n). Cheap and readily available because it was used on production Volvo's, plus well documented opening times etc. It might be worth your time/effort to tweak your chips for each of the Ford Racing options I've listed above, to make your customers' lives easier acquiring known-good parts which correctly fit the fuel rails?

Hilton

Its a modification for 87 fuel rails to replace the original rubber mounts for the fuel rail, used only in 87.

I posted pics of the solid spacers that are on my '87 in a thread somewhere here, which replace the rubber buffers with a longer stud and piece of metal. I'll see if I can dig it up.

edit: pics I posted in this thread: https://rennlist.com/forums/928-foru...-s4-model.html

Mongo

I am going to give JFrahm's method a try with the dash 012 o-rings and see how they fit prior to making my conclusion.

Jfrahm

A different injector retention method might be "better" in some Platonic way but I just put at least 100 lbs of force on one of these injectors with the clip and O ring, and it stayed put. So honestly it's gonna hold and a more perfect solution is just not going to work any better. The injector is not going anywhere and that's that, at least in my case. Couple that with what seems like an impossibility to pop the injector down and out of the rail and you are A-OK. If you are worried about it, ziptie it to the rail from below the connector. Crimeney. Do you people wear three belts and two sets of suspenders and then stay home just in case?

-Joel.

Mongo

I LOL'd.

Jfrahm

Interested in the amount of force that might drive the injector down and out of the rail, I quickly connected a fuel rail (with a regulator) to 75psi of air and gave it a go. I expected "not a lot" of force due to the small cross section of the injector inlet. I actually pre-tested this by fitting my my injector cleaning hose to the airgun and hitting it with 30psi to see if it was going to be scary. It wasn't.

At about 60psi I could easily hold an injector in place with two fingers of one hand. I tried holding the injector in place with two rubber bands from the post office and these held the injector in briefly, but then it popped off and scooted about halfway across the pizza box I am using as a workbench. If one could keep the injector from going crooked it seems like the rubber bands would be adequately strong to hold the injector in place. I'm out of ideas for reassuringly pathetic injector retaining methods for now but so far this has been encouraging. It'd be sort-of fun to clamp this mess to the proper bench with a strain gauge scale under one loose injector to see what it registers, but I am not sure I will invest the time. I do not think the force is more than 10 lbs.

Extra clips are pretty easy to find for BMWs, easier to find for GM in sets of 8 but they are slightly different and I do not know if they'd fit as well. Not sure I want to spend $8 to find out if they fit but the GM clips have a nice springy look to them. Too bad someone in the past failed to fit them to my blower car, but at least the injectors seem very solidly mounted despite this shortcoming.

Please note: I suggest running the clips and some appropriately secure way to fit them to your injector of choice. Clips are cheap and they are plenty strong. If, as in my case, the previous muppet has discarded them I suggest you get some and get them on there properly, despite it sure not seeming to matter on my motor.

-Joel.

Mongo

What is the difference between 70 and 75A o-rings? I am looking at the 012 for this application.

Jfrahm

https://www.oringsusa.com/html/durom..._o-rings.html:
"The hardness of rubber compounds is measured by the Shore A durometer; the higher the durometer, the harder the compound. 70-durometer hardness should be used whenever possible as it offers the best combination of properties for most O-Rings applications."

Joel: 75A is pretty common for Viton and I reckon it'd be fine in this application. Or 70. No big deal.

In other news I put my fuel rail on some blocks of wood and put a bathroom scale under one loose injector, and found it to press down with about 7 pounds when the rail was pressurized with a stock 944S2 3.5BAR regulator in place. The beat up and dodgy looking rail gauge I installed read about 57psi , which is about what was in the compressor, so I guess the regulator is a stuck (it never hissed) but hey that's fine for this test.

This force seems correct to me as I could hook a finger over the injector harness connector and slide the injector in and out of the rail cup like a trumpet valve with the rail pressurized. That felt like less than 10 lbs to me.

Mongo

Got my o-rings ordered. I will be keeping these injectors.

PorKen

Unless Roger has a problem sourcing the rebuilt 24# at some point...meh. If anything I might give in and make a (detuned?) 19# version.



Redo all the maps for slightly different 24# injectors? What about summer vs. winter weather, or running in a different gear than where it was tuned?

It's batch fired. All injectors firing twice per RPM, once onto a closed valve. No weather, road speed, etc., etc. compensation. Not going to be all that accurate or particularly efficient. Ever. There is no advancing or retarding of when the injector opens. Latency is just a matter of adding or subtracting to the overall injector on time which is handled at a low level by Adaptation.

Mongo

What is so different about these ones I picked up aside from design?? Just wondering if there is an incompatibility with the chips. I assume there isn't...

Hilton

Defensive much?

Go read my post again, I didn't at any point criticise your solution. If you want to tie bits of wire around your injectors it doesn't bother me. All I did was post my own opinion and analysis of the injectors I played around with in the garage.

I did my own testing, and drew my own conclusions. I recommend anyone else should do the same. Reaching a different conclusion to mine is not offensive to me - different people have different degrees of experience, tolerance for risk, budgets, and mechanical abilities, and sometimes I'm just wrong and can learn from others.

By the same token, be careful what you recommend to people on a public forum - they might follow your instructions badly and cause harm to the car, themselves, or others.