I've seen some people advocate facing the scoop backwards, which would negate any (questionable) ram air effect. One of those mushroom type scoops would eliminate that as well.
If you ask people why they run them backwards, you will probably get the same responses I've gotten. Forward allows rain to get in and I had one say that's how the body shop installed it and they knew what they were doing. This "pool" of people consists of only a handful Ive been able to ask. I ask just to see why they did it and not to give grief. The mushroom type are based on the mining/commercial systems with the big air cleaners. Again raising intake a bit.
The ram air benefits can be fairly considerable depending on a number of factors. I cant remember the math off the top of my head for air velocity equaling temperature drop but if you change temp 10 degrees it equates to 1 percent of power change. 50 degree temp drop would mean 5 percent power increase.
On my 04 TJ the factory pulls air from inside the engine compartment. I put my temp probe just after my air cleaner and went out crawling in a small canyon. The outside temp was a little over 100 degrees, my temp probe was reading almost 300 degrees. Not having enough ground speed to move the air out of the engine compartment, I was pulling heat from radiator, block and exhaust.
Using the above math and rounding it off, I was loosing 15-18 percent power at low speed.
I cut a hole in the fire wall and pulled the air from the cowl through a ford air cleaner housing. My air temp dropped down to ambient and would drop about 10 degrees below on highway.
Did I feel any difference, no. I have seen the numbers on the dyno's I have at work but, not with my vehicles. Its hard to duplicate ram air sitting. All we have is a big fan. I have seen the "cold air intakes" loose 7-10 hp with the hood closed because they pull air inside the engine compartment.
I guess what Im saying here is, people expect to feel some difference when they do a mod. You don't always notice it so people will say something based on what they think.
The only reason I don't have one is I don't want to cut my fender. Any little bit will help my 7k pig with the aerodynamic of a shoe box.
Scott