The paper discusses the influence of intake system design on engine volumetric efficiency. It notes that locating the air intake in regions of higher dynamic pressure on the vehicle front can slightly increase the pressure at the airbox, improving volumetric efficiency particularly at higher vehicle speeds. However, the magnitude of this ram effect is limited, on the order of a few percent, and benefits are also strongly related to intake air temperature and flow restriction.

This engineering paper analyzes a motorcycle ram‑air intake and reports that a forward‑facing duct can raise intake pressure slightly above ambient at higher speeds, increasing air mass flow into the engine. The authors state that the ram‑air system "increases volumetric efficiency and hence increases the brake power" at higher vehicle speeds compared to a standard intake. They also show that the effect is negligible at low speeds but becomes more significant as speed increases, confirming that ram‑air systems rely on vehicle velocity to generate beneficial pressure gains.

A CFD study of a motorcycle ram‑air intake in this conference paper finds that the dynamic pressure at the intake grows with vehicle speed, leading to a small increase in total pressure and air density at the airbox compared to static conditions. The authors note that this pressure rise improves the engine’s volumetric efficiency and power output at high speeds, provided that the intake duct is well designed and located in a high‑pressure region. They emphasize that at low speeds the ram effect is minimal and that the advantages are mainly realized during high‑speed operation.

Bill Jenkins is quoted explaining that hood scoop pressurization from ram air is a function of the square of vehicle speed, giving the formula: "0.0000176 x air speed in mph² = ram pressure increase in pounds per square inch (psi)." He calculates that at 90 mph the inlet air pressure increase is 0.142 psi, "just under 1 percent" over standard atmospheric pressure, which could yield a "corresponding 1-percent increase in horsepower" if the air/fuel ratio is adjusted. The article notes: "For every 10-degree increase in air temperature, there is a 1-percent decrease in horsepower," and contrasts hot under‑hood air with a hood scoop that "supplies outside air at ambient temperature," giving an example where dropping inlet air from 100°F to 60°F yields about a 4% (≈48 hp) gain on a 1,200 hp engine. It also stresses that while ram air can add theoretical horsepower, the extra aerodynamic drag of the scoop can offset the gain, leading Jenkins to describe it as often "a wash" between ram‑effect power and drag.

The whole point of a cold air intake is to get colder air, which is denser, and holds more oxygen for a given volume. The colder, the better. There is another critical element to cold air intakes for making power, and that comes in the form of increased and improved air flow. The key to gaining power from air flow is to minimize disruptions and obstructions to achieve laminar air flow and to increase the volume of air going into the engine, which will require more fuel to make additional power.

EngineLabs explains that as a vehicle goes faster, "the density of the air entering the air scoop increases dramatically at high speeds compared to when the vehicle is in a stationary position," and that beyond a critical scoop speed, the higher-density air has "dramatic effects on the engine tuning." The article states that when forward velocity passes 200 mph, "inlet air pressure can approach 2 psi over the current atmospheric air pressure," which can add "over 10-percent to the intake air density" of a naturally aspirated engine, provided fuel volume is increased to match. It notes that ram air from a forward‑facing scoop "helps the engine to ingest more air" at high speed and that correct tuning must account for this extra air mass, otherwise the mixture leans out and power is lost instead of gained.

A ram-air intake is an intake design which uses the dynamic air pressure created by vehicle motion, or ram pressure, to increase the static air pressure inside of the intake manifold on an internal combustion engine, thus allowing a greater massflow through the engine and thereby increasing engine power. The ram-air intake works by reducing the intake air velocity by increasing the cross-sectional area of the intake ducting. When gas velocity decreases the pressure is increased. At low speeds (subsonic speeds) increases in static pressure are however limited to a few percent.

A cold air intake system relocates the engine air filter outside of the engine compartment so that cooler air can be brought into the engine for combustion. Cooler air is more dense than warm air and contains more oxygen, which can result in a more powerful combustion event. By reducing intake restriction and turbulence, a performance intake system allows a higher volume of air into the engine, which can increase horsepower and acceleration.

For a race car or race boat, a forward-facing air inlet creates a ram-air effect above a certain speed. The air being pulled into the inlet has a higher density of air than in the surrounding atmosphere, which can create a significant boost in engine performance. Above 106 mph, there is pressure in the air scoop. That pressure increases with greater vehicle speed. Up to 3 psi pressure increase in the scoop was reported at 250 mph in this scenario.

Such were required the use of technical solutions capable of ensuring the pressure difference that ensures high speed filling. These technical solutions using air dynamics in motion along the bodywork and the phenomenon of inertional supercharging of intake manifold, known as RAM effect. In order to materialize the most convenient technical solutions it were required detailed aerodynamic body studies which were able to determine the areas characterized by high air pressure or areas where the air flow velocity is high enough to be able to ensure entry into the intake air mass flow rates capable of dynamic pressure increase. The areas are characterized by increases in values of local pressures from atmospheric pressure at high speeds, with the percentage up to 1%, using sockets in these areas of apparent air intake, arranged perpendicular to the direction of movement.

Cold air intakes relocate the system from its stock location, allowing it to draw denser, cooler air from near the fender well rather than warmer, thinner air above the engine, which improves combustion. When upgrading your air intake, you can expect a 5 to 15 horsepower increase, though this figure can vary depending on your make, model, engine size, and intake type. Turbocharged or supercharged applications typically see more significant gains from upgraded air intakes, while naturally-aspirated vehicles see the typical 5 to 15 horsepower jumps referenced earlier.

A cold air intake moves the air inlet outside of the engine bay so it can draw in cooler, denser air. Since cold air is denser than hot air, it contains more oxygen molecules per given volume. More oxygen in the combustion chamber allows more fuel to be burned efficiently, which increases the engine’s power output. In many applications this can free up several horsepower compared to a restrictive, warm-air factory intake.

The air outside the engine compartment is much cooler than the air inside the engine compartment. Cold air is denser than warm air, so the same volume of air contains more oxygen molecules. When more oxygen is available in the combustion chamber, the engine control system can add more fuel and generate more power. A cold air intake is designed to bring this cooler outside air into the engine, which can slightly increase horsepower at higher engine loads.

A cold air intake system is designed to provide cooler and denser air to the engine’s combustion chambers, resulting in improved performance and fuel efficiency. Cold air intakes draw cooler air from outside the engine compartment instead of the warmer air inside, usually at the front of the vehicle. Cooler, denser air has more oxygen, enabling efficient combustion and improved performance. Cold air intake systems increase the density of the air entering the engine, allowing more air and fuel to be packed into the combustion chambers. This results in increased power output from the engine.

The article states that hood scoops, when effectively designed, induct outside air into the engine: "When an effectively designed hood scoop is used, outside air is forced into the air intake, air which [is] up to 50°F cooler than air in the engine compartment." It adds: "Cold air is denser and includes a higher percentage of oxygen compared to warm air, resulting in improved engine combustion and added horsepower." It also notes that as vehicle speed increases, air speed and pressure at the scoop increase: "As road speeds increase, air speed and pressure increase, providing increasingly greater airflow."

The formula for theoretical maximum ram pressure ('velocity head') is: p = pv²/288g. So for example, at 150 mph (220 ft./sec.): p = (0.076 x 220²)/(288 x 32.2) = 0.4 psi (~11 " H2O), or about a 2.7% potential power increase. At standard air pressure of 0.076 lb./cu.ft., the velocity head per physics as in the above equation is 1.192 psi @ 260 MPH.

Ram air just means using a forward-facing air intake to gain some extra intake pressure. While it's appealing to imagine the forward velocity of a car being converted into free supercharge, the actual air pressure gain is extremely small at normal speeds. For example, at 150 mph, the pressure gain when air is efficiently brought to rest is 2.75 percent. A figure of 75 percent efficiency is usual, which reduces our notional ram-air gain at 75 mph to one-half of one percent.

The article states that "a functional hood scoop can increase horsepower" because it "works by forcing cooler, denser air into the engine’s intake" and that this "improved airflow allows for more efficient combustion, potentially leading to a noticeable power gain." It explains that the effect is speed‑dependent: "The effectiveness of a ram-air type scoop increases with vehicle speed. At low speeds, like city driving, the 'ram' effect is minimal… But at highway speeds or on a track, the increased air pressure forced into the intake can be quite significant." The author notes that gains can range "from a negligible few horsepower to over 15 HP" depending on scoop design, engine, and speed.

Anyway here goes, all based on the conventional formula for dynamic pressure, 'speed sq. times density over two', where density is set to one. Imagine that a 2500cc/1900Rpm four-stroke engine, with 100% filling of combustion chambers, would consume 380 liters of air, in an F1 car travelling at a speed of 300 km/h (83.3 m/s). When an intake area of 200 cm² seems about right, it makes for a speed difference of 64.3 m/s, which creates an extra static pressure of 2.07 kPa. Theoretically translating to some 15.7 extra horsepower if we started out with 760. Conclusively, a net gain of a mere 12 Hp.

You will not see positive manifold pressure unless the air speed coming from the scoop is faster than the air already moving through the intake. The theoretical maximum pressure rise from ram effect at reasonable road speeds is only a few tenths of a psi. Most of the gains from a good cold air or ram air setup are from getting cooler, denser air and reducing intake restriction, not from any real supercharging effect.

In incompressible flow at typical road car speeds, the dynamic pressure available from vehicle motion is given by q = 0.5·ρ·V². At 100 km/h (~27.8 m/s) in standard air, q is roughly 470 Pa (~0.07 psi), and at 200 km/h (~55.6 m/s) about 1,900 Pa (~0.28 psi). Converting this dynamic pressure to static pressure in a forward‑facing scoop can slightly raise the intake manifold pressure above ambient but only by a few tenths of a psi, corresponding to only a small percentage increase in air density and potential power, assuming the intake also draws cooler outside air than the under‑hood environment.

Reducing pumping loss through the engine improves fuel economy. Increasing AI pressure could improve fuel economy under certain conditions, such as wide-open throttle on a fuel injected vehicle, vehicles with carburetors, turbos, etc. But under low load with fuel injection, the higher pressure is wasted, because the throttle just restricts to keep stoichiometric. The essential problem is that, while many modifications make the oxygen at the AI more dense (cold, pressure), that delivers more power, not necessarily better fuel economy.

Contributors on this technical forum discuss that most so‑called ram‑air hoods mainly provide cooler outside air rather than significant pressure increase at typical road speeds. One user writes that "ram air needs much higher pressure like near 200mph with total seal to effectively gain hp" and that with a completely sealed box "you may actually get somewhere between 1-1.5 psi of forced induction starting at speeds near 100 mph." Another summarizes: "Ram air only works if the airbox is completely sealed to the hood and no leaks are present. Then it only works at high speeds, maybe over 100+ mph. Until then, it is just a cool air setup, which is also effective," indicating that cooler external air can slightly improve performance even when true ram pressure is small.

The highest static pressure rise would be a lossless, 100% conversion of dynamic pressure to static pressure. In reality it's less than this. To get a rough idea, at 100 mph you'll have about 0.18 psi max due to the ram air effect. Generally it'll be less than 1/4 psi, so not much. Boost Logic with SW's black MK4 Supra at the Texas Mile had a ram air intake system to the turbo and over 190 mph they noted about air fuel issues because of increased intake pressures.

The bad news is at normal road‑going speeds there's not a lot of pressure – I did some quick calculations: at 130 kilometres an hour or 80 miles an hour there's about 3.2 inches of water pressure available. That's a positive pressure above atmospheric, more than enough to make up for the pressure drop that occurs in the intake before the air reaches the engine. In most cars fitting a good high‑pressure cold air intake will improve performance, especially if the original equipment wasn't done very well in those areas.

A user discussing ram-air effects notes that scoop placement relative to high-pressure zones is key: "You'd get more ram air from a scoop behind the grill run to the airbox, then you'll ever get from the scoops in the performance hood. All you'll get from those scoops is cold air, no ram air." Another post emphasizes speed dependence: "At highway speeds you might see a very slight pressure increase, but around town it's basically just a cold air intake." These comments distinguish between higher-pressure air due to ram effect and just cooler outside air.

The product description explains the intended function of the ram-air scoops: "They're designed to force more cool, dense air into the engine compartment, which can help with performance, especially at higher speeds." It notes that by directing outside air: "the scoops can increase the amount of oxygen available for combustion, potentially improving power output when the vehicle is moving fast enough for the ram effect to be significant."

The product is marketed specifically as an air intake hood scoop: "Carbon fiber air intake hood scoop for 2021 RAM TRX" that "fits OE TRX hood" and is designed to work with the truck's factory intake path. While the listing is sparse on technical details, its purpose is described as providing outside air to the engine bay/intake system in a functional scoop configuration, rather than purely cosmetic.

In this installation video, the creator connects a hood scoop to an existing cold air intake, explaining that the goal is to route outside air directly into the intake box. Around the middle of the video, he notes that once the scoop is opened and ducted to the intake, it will "feed cooler outside air straight into the airbox" when the truck is moving, instead of drawing warmer underhood air, which he expects to help performance at speed.

This aftermarket scoop is described as a functional component rather than just styling: the manufacturer notes that their hood scoops are engineered to integrate with OEM designs and have been "crash tested and approved by major OEM Truck Manufacturers in the US." While detailed pressure data is not given, the implication is that the scoop channels outside air over or into the hood region, intended to work with the vehicle's airflow rather than against it.

Enthusiasts discussing a DIY ram-air mod emphasize ducting high-pressure outside air to the intake: one user writes that it makes sense to "aim for the 'ram air' from the front rather than thru the top" so that the scoop can capture airflow where pressure is higher. Another comment notes that cutting into the front bumper to route air to the intake is easier and can provide more direct high-speed airflow to the engine than a top-mounted scoop.