I'm actually making a true cai, or the closest to it. I've got the hole dremeled out which leads to my fenderwell area, which is where the washer reservoir used to be. This is for an s4. Starting at the MAF, which has the 3" filter adapter currently, I will be running 2.5" aluminum piping to the newly located filter. 3" to 2.5" couplers will be used from the maf, to the piping, and once again back to the filter.

Question: Will it be restrictive to have the 2.5" piping leading into the 3" maf filter adapter?

 

I used 3" all the way, however 2.5 shouldn't be a huge deal. The afm is going to limit flow more than any diameter change like that. The main reason to run this setup is to get cold air. I measured temps of a fenderwell intake versus stock box and cone in the engine bay and it blew them out of the water.

 

Hey. You're in Richmond? I think I saw you up at the 7-11 by carytown one day by the looks of your car. Nice ride.