"cold air intake" piping size

Try looking at www.ramairbox.com they have some neat stuff up here in Canada.
If your running a carb (float bowl vents) and you connect to the cowl, remember that's were your fresh air comes from for you heater system and air vents, there will probably be the smell of fuel in the car as well as being loud.
Ill be using FI but I'm getting cold air from thru the rad support.