Nunyas,
Cold air induction actually doesn't matter if the car is fuel injected or carburated. I'm not sure how familiar you are with older American muscle cars, but that was a big deal back then (Besides my MGB, I also have a '70 Pontiac GTO). Pontiac was the first company to have anything that I know of, and I believe are the originators or the name "Ram Air" as it was called on the GTO's and Trans Am's.
Oldsmobile had an idea similar to EMGEBE is talking about on the 442. The 442 had two long tubes that ran into the air cleaner (one on each side) that were fed from openings low in front bumper.
Chevrolet eventually ran a cold air induction but not a ram air style - the Chevelle was available with Cowl Induction. Cowl Induction was where a plate opened on the hood right near the windshield, but the opening faced the vehicle occupants. The idea comes from basic aerodynamics. Air wants to flow in a straight line, with a constant velocity and pressure. When the air flow hits the front bumper, some moves upward, and some down. The air that moves upward requires a large drop in velocity and a large increase in pressure to change direction. As the air gets to the front of the hood (bonnet for brits), it can flow mostly straight again, so the pressure drops and velocity increases (notice that if one goes up, the other goes down). When it approaches the windshield, it has to turn up again, meaning low velocity and high pressure. The air does not stick to the surface and take every shape of the car, but flows a little above it. As air turns up for the windshield, it curves, and the little area at the base of the windshield has air just sitting there, not doing anything, and it turns out using this air in the engine is great. If you look at a side picture of any car in a wind tunnel that shows multiple smoke lines, you can see where the lines change direction that the lines near it that were straight get closer together because of the pressure increase.
The SS454 Chevelle that had this (as well as a big block 454 cubic inch American V-8) made around 450 horsepower.
So anyway, cold air is also great for carburated engines because of it being more dense. A cooler, more dense charge is great for all engines.
EMGEBE, I've considered creating a ram-air duct on my MGB, but the series I plan on racing it in does not allow it. If you want though, my idea was just to cut part of the hood (3 sides of a rectangle) near the carbs and, leaving the part of the rectangle closest to the front of the car, bend the metal down using that forward edge as the "hinge" if you will. You would need to add some other metal parts in to direct the air right to the carbs, but it should be pretty simple to do. Just an idea at the end of a long story.