Connect a Scangauge or some similar instrument to your OBDII port.
Arrange for it to display "MAP" (manifold air pressure).
Turn the key on but don't start the engine. What the MAP displays at that moment, is what it thinks the barometric pressure is.
Now start the engine and drive around. With some straight and open road ahead, floor the accelerator. Note what the MAP displays under those conditions. Ideally this should be at the same altitude and on the same day as your engine-off check.
The highest MAP can possibly be without forced induction, is barometric pressure.
So if barometric MAP shows (let's say) 98 - 99 kPa (as it does in my car where I live), and at full throttle it shows 97 - 98 kPa (as it does in my car!) it means the entire pressure drop in the intake system up to wherever the MAP sensor is, is (in my case) somewhere near 1 kPa.
That is not very much, and given that there is always going to be *some* pressure drop, it pretty much means that there is nothing further to be gained by doing anything to the air intake system - which, in my case, is the stock snorkel from the outside of the engine compartment to the stock air filter housing. I made my own connector hose from the air filter housing to the throttle body to eliminate a resonator that was a royal pain to deal with. Then the stock throttle body and intake manifold.
If, on the other hand, at full throttle it is only showing (say) 90 kPa, and barometric was 99 kPa, then you've got some work to do and there's likely power to be found by doing it.
Bear in mind also that the biggest gain will likely be by making sure the temperature of the intake air is as close to the outside temperature as possible, as opposed to the temperature of the engine compartment. This is where aftermarket "warm air intakes" end up LOSING power.
The auto manufacturers are not stupid; chances are, your intake system already draws air from outside the engine compartment. Mine does.
