if you want better airflow, open your stock filter box and see if you can remove any barriers that cause the air to make any turns right before going into the tube to the intake. maybe see if the opening into the box is smaller than the tube to the engine and if it is, enlarge the opening to match. and do those openings match the size of the throttle body.
you can probably smooth the airflow track out and mmaaayyyyybbbeee get a little more flow by adjusting openings to be the same size, or larger then the throttle body opening, but other than that, without going to an oversized throttle body, you are really just messing around for fun. your stock box is already a cold air system that also cuts down on engine noise. a k&n, or other aftermarket system just gets rid of the noise reduction so you hear the revving and "feel" its faster. and most of the aftermarket kits actually turn your stock cold air intake into a warm air intake by not properly sealing out the hot under hood temps and using highly conductive metals that transfer heat versus low conduction plastics that are way thicker to help stop heat transfer.
unfortunately, if you put a temperature probe on that intake tube in the pic above, and one on a stock intake, the air in that metal tube will be a higher temp than a stock system so you are lowering hp running hotter air with more widely spaced oxygen molecules than cooler compact oxygen molecules.
how much though, you would have to run on the dyno to find out. most of the time those aftermarket intakes actually cost you horsepower when you actually run them on the dyno.
