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!!!

I thought the actual design is far from ideal? So why should replicating it be an option?

Just because there are even trickier parts out there doesn't mean that this is a good beginners project. it seems like you've come to the conclusion, that the airbox might be a bit difficult to start with. As someone who actually reached a point where projects like this are possible, I just wanted to tell you, that I think the intake is already fairly complex. Split mould, compound curved flanges, that are topics that will likely cause you problems, especially if you never done composites before.
This videos make it look quite easy, but only looking a video doesn't make you master those techniques. I really doesn't hurt to just start with a simple one piece mould. A cover ore something. Your experience from that will make any further part that much better. And it will likely save you both time and money in the end.
To the temperature topic: just making the intake out of carbon will rather increase the temperature of the air, as the tube will be (when made properly) is thinner than the original, and carbon has a higher thermal conduction coefficient than the original material.