intake?

how do intakes like these increase horsepower? http://www.urbanautoaccessories.com/gfx/products/cold%20air%20intake%20polished.jpg thanks.

I take it that you mean "why do polished air intakes make moer power?". By making the walls of the intake as smooth as possible, you can get less air to touch it (rough surfaces have more surface area than smooth ones), thus reducing the surface resistance. then there is the small turbulance that reduces the effective velocity of the air going through the pipe. that alos can create problems with density / flow patturns within the manifold that wernt designed by the engineer.

so smooth intakes are better

that wasnt exactly what i men but that really helps too. i mean how do intakes like that even though theyre not polished add hp compared to the stock one.

more air flow means the o2 sensory adds more fuel. More Fuel + More Air = More HP

Well the thing with polished intakes is that they allow for greater air flow but not as great velocity. Polishing an intake might actually reduce your horsepower because the fuel in the air will seperate because of a lack of turbulence.

The general idea is to move the air filter to a place in the engine bay with a lower ambient air temperature. The reasoning is this, colder air is denser, denser air contains more oxygen molecules, more oxygen means more fuel can be burned efficiently, and more burnt fuel means more power.

Hence the name...cold air intake.

The air intake tract should be as efficient as possible. It is the job of heads and the valves to created the proper turbulence. If the heads are doing their job properly, than you want to supply them with as much air at as great a velocity as possible so that they have more to work with. While not all heads do their job well, most newer cars' heads do.