On some mustangs the hood scoop is ther for show. I have a friend that has one and I checked out the hood scoop and all it was, was a scoop with a plastic wall. Same with the 2000+ Celicas, hood scoop with a plastic wall. Cant say much about muscle cars and impreza but that is a good question.
How do they keep the water out?
Hmm, water is a good thing, on my friends Impreza, he has a TMIC, and water only cools it down more. None of those cars actually have their intake sitting right there, even the mustang just has the air comming in for extra cooling.
I would go with a vented hood, NOT one with scoop.... I think it just doesn't look right!!
And vented hoods usually have a tray you can place under the vents for when it's raining or carwash and etc... and that tray just redirect the water and as far as possible from your air filter..
I'm still doing a research on that, since I really wanna get one soon
Cutting a hole in your hood and trying to make a scoop = $$$. And not only that, your guys hoods are aluminum. Can you even do welding on that?
And what for? To get cool air to your WAI? The cost is going to go well over the cost of a CAI. Try driving on the highway for a bit, then immediately get off, pop the hood, and touch your WAI. I bet you it's cool to the touch. I have a homebrew short ram intake, and I was planning on make a heatshield box and a ram air extension. But then I found out my intake was cold to the touch. Cool outside air is reaching my intake while driving.
the engine temp is one thing i immediately noticed on my altima, it never gets even warm, i mean past the point of usual temp, even while running it hard, racing and such, doing top end runs and staying at 5000-5500rpm for a matter of about 35sec. or so, it jus never seems to over heat, and the WRX, the intake is for the top-mount intercooler on the car, as opposed to having a front mount intercooler where the air that comes toward your car goes into it, the scoop sucks air from above
and yes, a front mount intercooler is more efficient and better for hp gains, but remember, if u have a low car, it gives u a much better chance of water getting into your intercooler, and i know they have parts that redirect the water away from the intercooler on front mounted ones, but this is jus a lil less of a chance