3D Printing Strength

Why wouldn't it be 3D printed? Not strong enough? I assume it's a fairly specialised item and shape.

You'd need to be able to 3d print POM, though (or use CNC).

3D printing doesn't help much to reduce prices for mass market manufacturing. And the materials that can be used in most 3D printers still aren't strong enough for applications like this. Milling, casting, and forging can generally produce stronger, lighter parts.

Does it make sense to 3D print these parts rather than injection-mould them?

Can 3d printed parts handle higher pressures very well?

This comment goes a bit too far the other way. 3D printing is a manufacturing technique with its own possibilities and drawbacks which you need to be aware of, but it's very possible to make engineering-grade parts with 3d printing - for some things, it's even the state of the art. You can eliminate layer stress lines with annealing, and you can print interior shapes that would be impossible to injection mould. I myself have made polycarbonate fan blades, only a few mm at the thickest

The end of that first sentence you quote, "must withstand huge temperature ranges and enormous forces", kind of gives away the answer -- this isn't made from "standard" materials. 3D printing is an amazing technology that's rapidly developing, but it's not quite that far yet.

Oh yea CNC'd is more likely. A 3D print would never survive.

For parts, additive manufacturing (3D printing) might be a suitable option? You can even print metal these days.

Could a 3D printed nozzle of some sort improve its characteristics?