which is healthier for a n/a engine - more air or colder air? in other words - for a non s (no intercooler) would a CAI which got air from under the hood be helathier for the engine than the stock air box since the engine could breathe easier?

also, which type of filter is healthier for an engine - traditional paper, gause/cotton or foam. once again - is it helathier for the engine to get more air through a k&n type filter or cleaner less oily air from a paper filter?

 

More cold air is best. Increased oxygen allows the ECU to add more gasoline and make more power. So I would say cold air is denser and has more oxygen.

Under hood temperatures seem to be reasonably low as long as the car is moving. A good quality oiled foam filter would be my choice.