Since the stock inlet hat is fairly restrictive on these better off capping the hole with a little filter. i use a valve cover breather that they use on stock car valve cover tubes, 1.5" or something like that, every little bit helps but dont do that if you drive the car in the rain a lot Just use a black rubber plumbing cap with a hose clamp from a hardware store if you want to cap it, its a little large but works fine.

I dont remember how much it lowered the IATs exactly but it was enough where I left it open (with an air filer on the bypass) and lived with the noise.

 

I got mine form Home Depot.