This is the updated design from my older cold air intake published elsewhere. Significantly better flow, CFD says it will outflow a typical 90 degree elbow.

Included are two files, one with a shell thickness of 1.2mm and another with just a skin that can be shelled to whatever wall thickness is needed. For clearance, do not expand the skin more than .5mm. This design was intended for a thin wall thickness.

Engine bay heat soak can causes the part to see very high temps. Enough that PLA is a non starter, and ABS is marginal. My plan was to print these with a 1.2mm nozzle in straight polycarbonate (not one of the more easily printed PC blends)- For printing I was planning to hack together a gcode file from two sperate slice results, with the elbow side at the bottom transitioning into a vase mode print after the bend.

To set this part up you will need:
Assuming a MAP based aftermarket ECU you will need:
A first generation miata
Green Filter 2451
2.5" silicone elbows (90 and 45 degree)
A 2.5" crossover tube, try to find something thin wall. 2mm aluminum tubes have less ID than this duct
*IAT sensor best placed into the filter end to keep sensor from heat soaking. Easier to tune hot restarts

For best fit, you may need to adjust the rubber bumpers that control latched hood height. Also, some cars will need clearancing with a few hammer strikes to the interior of the hood structure just above the duct bend. Do not slam your hood with this intake.

More info in the very long miataturbo thread:
https://www.miataturbo.net/engine-performance-56/3d-printed-intake-n-na-miatas-76193/page28/
And in this blog post:
http://www.wrenchgame.com/2018/07/12/updated-miata-air-intake-design-now-available/