hi, saw alot of topics about intake like short ram vs cai, but wanted ask about the pipe diameter, how much of a difference does it make ? i know air has to flow nicely, but if the diameter is too big there will be no flow.
anybody know the right answer ? thanks.

 

Use the size that's being used for your car by brand names (aem, comptech, etc.....) If there was any benefit in going bigger/smaller they would have done it.