RAM AIR INTAKE

In any body of moving air (or other compressible fluid), the air’s static pressure is inversely proportional to its velocity. To take advantage of this principle, the cross-sectional area of a ram scoop’s intake plenum typically starts off small and gradually increases. As a result, air enters the plenum at high speed and then slows as the plenum widens. As fast-moving air continues to enter the plenum, air begins to pile up and its pressure increases. If this high-pressure air is admitted to the engine’s intake valves (assuming the pressure is not diffused before that), it can be used to provide a mild supercharging effect. A functional ram scoop generally also serves as a cold air intake, although the reverse is not necessarily true.

The benefits of even a properly designed and well-placed ram scoop can be difficult to quantify because the supercharging only occurs when the vehicle is moving and thus can’t be measured on a stationary dynamometer (unless you also have a wind tunnel). It can also be tricky to determine whether any power gain is due to the ram effect or simply the benefits of admitting cooler air to the engine. However, a good system under ideal conditions might conceivably produce a power gain of up to about 10%.