Hey, I'm new here but have always loved cars. This project will be for an Audi S4. For our car platform however, the intake options are less than ideal - otherwise I would buy one. 

An expensive but poor design:


This intake design is ideal, but it isn't for our car and serves as the inspiration for the project:


That said, my idea is to construct a snorkel that could work in conjunction with one of the heat shield only designs as such below:



Now, while I have never done any projects like this - I am pretty handy and learn quickly. I am looking to make a permanent mould, so that it can be replicated... but I have to design the shape first. I'm sure more questions will arise, but the two that I can think of are:
1. What is the best method to create an accurate mould?
2. If I make it a two piece that surrounds the filter, how do I set the threads for the screws to bolt down the lid? (See below for example):



Thank you SO MUCH in advance!!!

It's sort of a bit grainy to tell, but they look like nutserts to me.

Heat resistance is all down to the resin you're using. If you're planning on wet laying these, there's quite a few high temperature resins that will handle 160+C with a post cure.  If you want to infuse you may struggle to find anything higher than 95-100, especially if you arent wanting to buy in bulk. Both wet lay and infusion will require a post cure up to the planned operating temperature in order to realise those temperature capabilities, so you would need a solution for getting them to that temperature for a few hours. Otherwise, if you have the facilities, pre-pregs will do about 120.