ok i got a 3" cowl hood for my car, im wondering if there is something that i can use to seal the opening in the cowl to the base of the airfilter, or can i use a velocity stack for it?
what are my options?
what is the best route to go so i get the most air from the cowl into the engine instead of sucking in the hot under hood air?

 

that's a dismally un-descriptive title ya know

A velocity stack is usually taller than that, and sticks out a hole in the hood, I don't think that's what you want to do.

Look for a cowl hood - carb setup, you might be able to buy a kit for it. Otherwise, you want to build some sort of plate that will go above your carb, to replace the bottom of your air cleaner, then your choice of air cleaner, with a tall foam "lip", to mate with your hood. I've seen it done in many different ways, one guy had a monte carlo, with a gigantic K&N plate filter, or you can do something like this, but without the fact it's for a power bulge hood:
http://www.hioutput.com/tech/air2.html

etc etc.