They don't make any intakes for the 4.2L V8.
Would it make a difference if I made my own? Or should I do something else?

 

Depends on what you had in mind as to what the intake looks like? Describe it ??

 

Basically replacing the box with a cone and replacing the rubber tube with a metal(or whatever its called that the intakes are made of)
The sensors wills till be in place.

 

I know that there have been several companies who have come up with a CI for the B6/7 S4. What Audi has done in the original design is a CI intake. The problem with aftermarket intakes is some of them don't deal with the extreme hot engine bay temperatures in our cars. The only really good system that I know of is the Carbonio one. I would avoid the cone sitting open in the engine bay scenario. Other than that I would recommend frequent filter changes with the OEM box.

If you could come up with a good CI intake that utilizes a less restrictive filter let me know.