You have to realize that car companies have a multitude of regulations to make the vehicles conform to. One being so-called 'noise' laws. The exhaust noise is one thing, but intake noise is also severely regulated these days.
My expe has two "cans" bulbing off the intake tract doing nothing of consequence that I can see except requiring that much extra plastic in the build. All they are there for (IMHO) is to break up harmonics from the intake tract (they help make it quieter). Apparently that intake wooshing sound is objectionable to some nursing home residents.
I'm no expert on fluid dynamics but air rushing past a hole in the side of a tract is going to depressurize the area beyond the hole, in this case one of the open liver shaped boxes on the side of the intake. I've heard some call it a reservoir. HUH? An wind reservoir? That works for vacuum or pressure but not for moving air. I've never seen anything that can store wind.
So,whether this empty boxed area has any actual usefulness beyond breaking up noise I can't answer, but for the life of me I can't figure out any other purpose for them.
My point is the OEM is a compromise at best. Piping air with smooth large radius bends will eliminate turbulence in the air stream. The slicker the inner walls of the tube the easier the air stream flows also. The sides of any tubing no matter the diameter cause restrictions to air flow. Friction is the cause of that. The boundary layer in contact with the outer diameter of the flow path slows the entire flow down. Now look at all the corrugations, joint's, flex tubes, and holes and bends in a stock system. It's a wonder any air gets to the intake at all.
Put a simple pipe in the inlet of the intake mouth, put a filter that has very little resistance to air movement through it and the air stream into the intake is going to be much faster with less turbulence. Turbulence is the mixing you get when stirring a glass of something, it's not something you want in this portion of the intake system. Once the air gets past the intake valves is where more turbulence is better.
The entire idea is to get as much laminar (smooth) flow of air to the mouth of the intake as is possible at all times. For comparison, look at the intake tract on a big (semi) truck engine. A supersized filter, then round metal or plastic tubing with smooth radii going to the turbo, then even smoother round(ish) shaped tubing going from the turbo to maybe an inter-cooler and then back into more round(ish tubing where it can straighten its flow out before getting to the intake. A diesel is normally fed as much or more air than it can use. The turbo packs as much into a cylinder as the design allows.
The same can be said for a throttled engine. More air is good as long as the amount of fuel is capable of making a stoichiometric mixture then all things work better. This is where the aftermarket cold air intakes shine. Colder air is denser therefore there's more of it in a given volume. Which is a sloppy way of describing it.
The round tubing flows better than all the bends and irregularities of the OEM intake. The implementation in actuality is still a compromise. An OEM pulls air in from (normally) inside a front fender opening. This spot is better than most aftermarket systems that try to isolate the intake filter inside the engine compartment off to the side by a fender. This is actually a lousy place to pull air from even with the intended isolation panels. Especially considering the panels are often made of aluminum or thin sheet steel, neither of which don't really stop much heat transfer. But the objective is to get your money and at that work beautifully! Nevertheless, the front corner of the engine compartment is going to be cooler than anyplace else in the engine compartment so it remains a compromise.
The ideal solution is those fording kits for overland expedition purpose built vehicles. They have two benefits, they can be placed in the forward facing position to help ram air into the intake tract at speed, and they pull much cooler air from many feet over the pavement. For fording deep water the intake is turned rearward so large water splash won't get sucked in or when it's raining really hard, although they do have automatic drains on them.
In essence, a good flowing filter is necessary, a great flow path is a good thing too. As in all things automotive, the compromises are never ending. Great flowing filters apparently don't filter very good, and great filtering filters don't flow all that good.
