TOP HALF: There are cast- in plastic support ridges that form a criss-cross pattern in the upper air box. Some of these run perpendicular to air flow. I guessed that by removing these perpendicular ridges, especially those closest to the MAF, that volume and velocity of air MAY increase. It also reduces weight. Structural integrity is still maintained, as is filtering ability.
BOTTOM HALF: The side of the air box facing the front of the truck was removed. The ridges in the bottom half were contoured when possible, to smooth flow. There is a small hole right near the headlight support where cool air comes in. Thats the reason I only cut the front, and not the sides, like the picture shows. I don;t want hot air from the engine compartment feeding to the engine, and want max protection from splashing. The amount of dirt in the fender below the air box is amazing, and it was not just dust, it was pebbles and stuff. This is just my opinion and what I did. Its not right and its not wrong. Its just me.