By sealing the air box you are bringing in outside cold air only which will make more power than hot engine air. To compensate for the small air scoop one just needs to remove the rain baffle form the hood scoop as this will increase the size of the opening dramatically. With the oiled green filters there is zero chance of water getting into your engine. I have driven at 80 mph in downpours so hard I could hardly see in front of me and I took in zero water.
I don't see reducing the wide width of the airbox's inlet down to the size of the hood scoop with much less area as a plus.
Along with that hole in the hood just not having enough area, most any flush mounted scoop lies in slower moving boundary layer airflow along the hood rather than faster moving air a few inches above the surface. A scoop with an opening that is flush with the hood surface is essentially in dead air...
If a 500ci engine needs 140 sq inches
minimum air filter area at 5800rpm, how does restricting initial inlet airflow through a much smaller hole in the hood lying in the boundary layer's slower moving airflow make sense?
I've experimented with blocking off a G2's airbox outboard of the NACA duct's opening-forcing the airbox to breathe only through the NACA duct, and I noticed a loss in power as rpms rose
before I got out of 1st gear .
I've also measured temps at the front of a G2 airbox's entrance at 45-50mph, and found no indication that engine compartment heated air is somehow
moving forward at speed-past the radiator support and all that paneling etc, to find its' way into the front of airbox.
I doubt that IAT's measured at the airbox entrance are influenced by engine compartment air temps at all once a car is moving faster than 5mph or so.
My bet is that you're losing way more CFM by only allowing air in through the hood scoop, than any perceived loss of HP due to heated air somehow finding its' way forward.
