A typical stock fuel injected motor is rated at about 85 % V.E. This means that out of the 346 cubic inches of air your motor could theoretically take in, only 85 % of that volume enters the cylinders. This translates to about 294 cubic inches of air. Some all out race motors can reach 100 % VE and supercharged or turbocharged motors actually exceed 100 % by forcing the air into the motor. Not everyone can afford a supercharger but there is definately room for improvement for the stock motor if you make it easier for it to get air into the motor for combustion. This is what ram air does.

As speed increases, the air entering through the sealed ram air kit actually becomes pressurized. This positive pressure helps to fill the cylinders more efficiency and raises the VE of the motor. As the VE increases, the motor becomes more efficient and produces more HP and also gives you better fuel economy. You will also find your throttle response dramatically improved. The motor is working less hard to fill the cylinder and is greatly assisted by the high pressure air. The faster your go, the greater the pressurization effect. This is similar to a mild supercharging effect.

The second benefit of a ram air system is that is supplies the engine with colder air than what it would normally breathe. Colder is more dense and contains more oxygen for the combustion process. For every 10 degree drop in intake air temperature, you can expect 1 % more HP. The ram air kit supplies cold air from the bottom of the car which is forced into the sealed air box. Unlike the stock system, the ram air kit does not let the motor breathe superheated air from the engine bay. Additionally, the computer detects this colder air and adds additional ignition timing. This makes more HP!