The plastic intake resins are fiberglass filled, not really do-able with current 3D printing.
But you can 3D print a master in casting wax, then use that for an investment casting in aluminum.
There are also folks making sand molds with 3D process, the sand is held together by a deposited binder.
Another option is to 3D print one in polyjet or other high accuracy method. Accuracy being key as long as material isn't overly brittle (vero white or similar would be good)
Then use the printed one as a mold to pour Plaster of Paris cores.
Seal the cores and coat with liberal amounts of mold release and then lay gelcoat and fiberglass over the plaster.
If the plaster of Paris is difficult to remove, mix in cornstarch (start with 1/2 as much as the plaster) to soften it and make it easier to break up to remove from the fiberglass.
Or use the plaster molds to thermoform polypropylene or hdpe. Pour the plaster core with a 1/2 pipe sticking out about 6-10 inches. This requires and old oven or understanding wife. You want to have your mold only a step away from the oven.
Drill and install a hose fitting in a cap on end of a 12-16" long piece of 1-1/2" pipe and connect to a vacuum pump with a shut off. Clamp the piece of 1-1/2" pipe horizontally with a slight upward tilt in a vice with the open end facing you and 6" sticking out.
Prep the mold by placing the pipe from the plaster mold into the one clamped in the vice. Put a nylon stocking over it and tape it around the large pipe to keep it tight.
Heat the plastic sheet on a flat sheet metal plate in the oven until clear. Silicon or teflon spray will keep the plastic from sticking to the sheet.
Once the plastic is clear, quickly lift off the sheet by two corners ( using bottom corners will make sure the side that was facing up on the sheet now faces away) and drape over the mold and onto the large pipe beyond the stocking.
Bring the loose edges together under the mold (and at end toward you) and press them together to take a majority of the air space around the mold out. Turn on the vacuum and make sure all air bubbles are removed and the seam is tight underneath. If you don't press the seam together again after turning on the vacuum you may end up with gap along there.
Once is cools you can cut off the ends and break the plaster mold to remove it. The plastic can be sanded and polished to finish the ends.
Was doing some research last night, discovered that same problem of not being able to print with glass fibers, so printing a finished product in nylon 6/6 is out.
So the options now for 3D-printing a finished product are coated ABS (explosion-prone, teetering on the brink of melting problems) or coated sintered metal (still possibly explosion-prone and expensive).
Other options are 3D printing a form for aluminum casting, CNC'ing aluminum billet ($$$), good ol' fab work (laborious or costly depending on how much I DIY).
Thermoforming the HDPE sounds like at least as much work as shaping metal, but it could be a good option depending on the weight savings.
Can they print with PEEK? PEEK is great unfilled and high temp so likely can't print but look and see.
I have PEEK in my flat head harley intake for bushings (compression ferrels) and will be using peek coated bearing cages in my RD400.
You can print in Ultem, which is high temp and rugged.
The problem is that it would be done with an FDM process, so you need to do some sanding and polishing to if you want to produce a smooth surface.
Doesn't look like 3D printing in PEEK has been done yet, but printing in the similar PEI/Ultem seems to be fairly common.
This handy site lets you compare materials:
http://www.makeitfrom.com/compare-materials/?A=Polyetherimide-PEI-Ultem&B=polyetheretherketone-peek
^I figured some sanding and polishing would be necessary in any case.
GameboyRMH wrote: I've been thinking about the design of an ITB adapter and it's getting fairly complex and potentially chunky - not large in overall dimensions,
do tell??? 
I haven't drawn up any plans yet but I'll have no trouble keeping at least as much firewall clearance as with the T3 adapter.
In reply to GameboyRMH :
What was the final out come? What did you use?
Still saving up money for the next and final batch of engine mods, which will be ITBs + "Stage 2" cams + shimless lifters + maybe some reinforcements for high-RPM use like a billet oil pump gear and crank ladder bars. I saved up 7 years for the light restomod that included swapping in the 4AGE, and at this rate I'd say it'll be a couple more years from now until I do another big job, which could be the engine work, a major suspension mod + new wheels, or a Quaife diff.
Looks like the best material available now is NylonX, but Nylon 6/6 or Ultem could also work. Burdickjp is also working on 3D printing ITB stuff and has produced some parts already.
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