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Author: Subject: Threaded Injector Nozzles

posted on 4/7/22 at 10:25 PM Reply With Quote
Threaded Injector Nozzles

Hi peeps,

Is it possible to tap the nozzle of a fuel injector (probably only on extended nozzles)?

I doubt it is due to material type or wall thickness, but just wanted to hear the opinions of the more learned than me (i.e. everyone).


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posted on 5/7/22 at 06:30 AM Reply With Quote
Tap as in internal threads?

What are you planning to achieve?

If you mean cutting a male thread and retaining them in a tapped hole, I'd think it would only be possible with side feed injectors (I don't think there's enough meat with any layout really) but your injector plugs may end up in all directions when the injectors are seated. Top feed would more than likely interfere with the fuel rail.

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posted on 5/7/22 at 08:51 AM Reply With Quote
It would be adding a male thread to the outer face of the nozzle.
My plan is to convert a zxr-400 cylinder head from carb-fed to efi; but I want to try and keeo the injectors out of sight a little.
From what I can tell the main body of most injectors are plastic, but the nozzle where the fuel comes out from is still metal.
Underneath the heads' inlet tracts there appear to be some m5 bungs (I assume originally for vacuum or idle control) that could be expanded to m8 (nozzle diameters appear to be approx 8mm); my thinking is could injectors be threaded in and allow for a simpler inlet manifold.

The idea about side feed and awareness of misalignment of injectors and plugs is something to be mindful of and to look at.

Hope this makes sense of what I'm trying to achieve.

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posted on 5/7/22 at 09:15 AM Reply With Quote
I see what you're planning, but it sounds like it will drive you to a compromised solution if it were possible.

The injector wants to be spraying at the back of the valves so running them underslung, you'll always be spraying into the roof of the port at best. It will probably work, but might not run as well as a more optimised solution. That said, neither will carbs 90% of the time.

A bigger risk is that injectors aren't mechanically designed to be cantilevered from the nozzle so would need support at the other which case a traditional arrangement with top feed injectors with o rings in bosses is probably as easy to implement - it just needs some welding and machining. A broken injector body could be quite catastrophic.

There are a number of very competent high strength adhesives for close fitting cylindrical assemblies, loctite 648 for instance, but would need heat, 250C ish, should you ever want to disassemble the injector. Check fuel compatibility too. This would let you use top feed injectors though as you don't have any orientation constraint with the thread, but would still need good support.

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posted on 5/7/22 at 09:37 AM Reply With Quote
Yeah, it would be a compromise but as you say I'm not looking for the most optimised solution; just seeing if I can use as much of what I've got without adding too many new components.

I did wonder if a cantilever action would be detrimental; but if a top feed fuel rail can be securely mounted, it would hopefully reduce the risk of breaking injector bodies.

Adhesives are an interesting idea, but as you say a heat resilient one would be a faff to remove, which is why I was wondering about a threaded connection.

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