There is a lot to be said for a rear facing scoop on a boat. Not because it takes advantage of the high-pressure area near a car's windshield, but in the event of crossing another's rooster tail or taking on a scoop of water.
Regarding a scoop functioning at low speeds, aerodynamic forces can be felt at meager speeds by simply sticking your hand out of the window of a moving car. The forces increase four fold as the speed doubles. The opening on a forward facing scoop can be made larger to take advantage of ram affect at slower speeds.
Some issues I have experienced: once the ram affect gets to the point where "boost" is actually generated, as in the case of a Bird Catcher hat mounted on a tunnel ram, the rear cylinders tend to run leaner than the front. Scoops mounted on carbs where there is turbulent air above the venturi or where air speed is high shooting across the top of a carburetor reduces booster signal. If the carbs are not functioning properly, you will never realize your peak potential.
I like to compare anything connected to the induction to cylinder head porting. It has always bothered me when somebody spends big dollars on ported heads, then bolts on some sub-standard induction and wonders why their dyno experience was less than hoped. The induction system is really everything in between and including the combustion chamber/cylinder and the atmosphere, which also includes the scoop. In my opinion, form follows function.
Just my $.02
Cheers,
Joe
