I installed a ram air intake scoop on my four wheel drive 2004 Toyota Tundra Double Cab a few years back. Changes I recorded:
- 1.5-2 MPG increase depending on driving conditions
- Truck stopped downshifting on hills
- Better passing power from 50 to 90 MPH
The ram air intake scoop gathers and forces somewhere in the area of 11 times more air than the engine can ingest at 70 MPH.
There is a website that claims mounting a ram air intake scoop below the bumper places it in a region of negative pressure or vacuum but this does not hold true for my truck. Using a homemade manometer I recorded 3.5 water inches of pressure in this area running the highway at 70 MPH. The scoop connects directly to the stock air box with a True Flow drop in-filter.
I have never been able to draw (or force) water up into the air box or engine - even in driving through six inches of standing water. I would not have done this deliberately but I was trapped in my lane with nowhere to go.
I had pictures to post but they are too big. I would provide links to the pictures but I have not made five posts yet.