The idea behind ram air is that you have an intake that takes advantage of the pressurized air in front of the car at high speeds. I think the term was first used in a production car by pontiac back in the 60's. A ram air system is basically just an intake that is strategically situated at a high pressure region on the front of the car. The added pressure can result in a little extra power at high speeds.
the key is you have to be at speeds high enough to actually get extra air into the intake. i don't know much about it but i'd estimate probably no slower than 30-35 mph...so if you're thinking about off the line gains, circumvent this. it won't do anything.