Let's suppose that an engine uses 1000 CFM of air. That is 1,278,000 cubic inches per minutes. If one has a hood scoop that measures 6X6 inches in clean air, that is an air velocity of 2958 feet per minutes, or a mere 33mph. What this means, at wide open throttle, is that a 1000cfm engine needs to be travelling at 33mph before its 6X6 inch scoop in perfectly clean air is no longer at a partial vacuum relative to the outside air. Thus the cute little hole in the signal light used by Hellcats is a chokepoint for the airflow unless the grille shape can raise pressure enough to overcome it's roughly 1/7th size of a 6X6 inch opening if it is using 1000cfm, and it is using more than that. with both signal lights used for an opening, the air velocity through both of them for a tiny 1000cfm of airflow would be 123mph through both openings. To have to travel 123mph to get 1000 cfm is suboptimal, as most people don't do most of their acceleration at that speed and above. 188 cubic inches (one intake stroke every two revolutions) times 6500 RPM gives 15.9 cubic feet per second, or 956cfm, but those of us who know math know that with the supercharger, the engine is using more than 100 percent volumetric efficiency, due to the Hemi heads PLUS the supercharger. What is the point? The point is that the puny little air openings for the Hellcat are insufficient to keep the engine fed with fresh ram air until speeds reach WELL over 123mph. The first-generation Mazda RX7 GSL-SE had a much superior intake system of at least 12 square inches or so fed from the high pressure zone right in front of the radiator bulkhead, and that was at about 1/5th the horsepower, or 200cfm or so. On another note, that is why Hellcats feel like they are trying to climb the air so hard once you get above 123mph, as you are now getting greater than atmospheric pressure being fed to the engine, aka, free boost, a total of about 0.375 PSI at 100mph. But, the object of this is that air filters are less of an issue in the overall airflow if they are placed, as they were with the Hellcat, in the already-compressed air stream fed from a scoop. When a body of air is moving slowly enough, such as the roughly 2.5 square feet of effective area of a pleated second-generation Hellcat filter, the air being above ambient pressure makes the loss due to flow drag of the filter itself less significant. So, in short, use the biggest posssible filter or, better yet, multiple filters for your car and place them in the intake tract in such a way that the air passes easily through them, unlike the laughable tiny paper filters perches on the top of individual Strombergs, for example. a "Stromberg" is a small carburetor. The issue with this, of course, is that it requires volume. If K&N made a 2X2 foot pleated filter that could somehow be rigged to fit in or under a Demon hood scoop, Then placed to angle upwards from front to back, one could experience even more performance if the associated ducting was shaped to take advantage of it, at the very rear of the scoop. At 1000 cfm, that would be an air velocity, (assuming 3x the overall area due to pleating) through the filter, of a mere 1/6th of a mile per hour. This would effect the intake air pressure in an almost negligible fashion. One problem with air filtration obstruction/drag is that it gets worse at the square of the air's velocity. This is less of a problem on a turbo car, as the turbo will just spin fast enough to boost the intake air to its set PSI. Superchargers, however, don't have this luxury. There is a reason drag racers don't use air filters on their directly-facing-the-front-of-the-car superchargers and turbochargers. Multiple filters trump single filters of the same size. If you live in a not-very-dusty area (such as the Pacific Northwest during the drizzly months) you can eliminate the filter if you really want that last bit of efficiency or speed.
This is true with most hood scoops. While drag racing, the shaker on my 1971 'Cuda did not add any hp. until I reached the top end and approached 100 mph. Read these informative articles. https://www.allpar.com/threads/hellcat-demon-and-redeye-power-levels-explained.235463/ Evolution of Hood Scoops | Dodge Challenger Forum
Scoops would work best if place in clean air or at the grille opening (famed high-pressure area) and if they were large enough to flow maximum air unrestricted at low speeds. The closest I've seen in a Challenger is the Drag Pak. The Demon scoop, shaker, and the SXT's scoops are not optimally positioned to take advantage of pressurization due to facing clean airflow, and allow the air to ramp over the scoop. No race cars use scoops that look like the ones that get used on factory street cars. But even the race cars from the factory looked better. Iterations of the Drag Pak: scoop mainly for blower cooling: A bit of boundary layer bleed: The new reigning dominator of the racing series in which the Drag Pak competes: You cannot see it, but the top several inches of the grille are entirely take up by the radiator-width scoop that funnels air into the engine. The radiator is kind of short in the race car. The top of the grille is NOT occupied by the radiator, but by the intake scoop. Rear view of radiator and scoop area: You notice how Mopar put rubber flap-valves on the radiator shroud to allow air to blast through but block air from being sucked into the read of the shroud by the fan? Mopar, like the USA, will rise again, in spite of the braying and shrieking of those who pleasure themselves to the defeat of masculinity and freedom in the world, such as many EV lovers, the mentally ill acolytes of Thunberg who crow with delight at the idea of the V8 going away. Pro Stock intake: Notice its placement: The front grille.
Not a chance. That thing's a collector's item. The dealer was surprised, I think, when I brought it in to fix some CEL and the entire car was utterly, completely, bone stock, mechanically. I even got them to throw on some Mopar splash guards. Were I to modify one, I think I'd prefer to start with a salvaged Hellcat to save it from the crusher or something. It's like adopting a dog from the pound instead of doing surgery on a purebred to give it floppier ears or whatever.
When designing an intake system for a car for FREE horsepower, you would be best served, if you were really thorough, to do some dynamic air pressure measurements at various points around the car and identify the highest-pressure zones, and continue to do measurements of your intake tract leading to your oversized intake throttle body as you experiment with various fresh air intake placements. Then, you calculate your maximum desired air velocity and size your system's minimum cross-sectional area (CSA) to keep your air velocity below that level at your prioritized target speed. The one pictured above on the Drag Pak near the grille is the best factory-offered air intake I've seen since the Ford Thunderbolt. See this pressurized beauty: Where is it fed? Right at the grille. Those two inner light bezels are sealed to the air intake hoses.
Further, back when Pro Stockers were far more glamorous and sexy, they had the "wind tunnel tested to add ZERO drag" giant hood scoops on their cars towering over the hood to gulp the tunnel rams and dual split Dominators. Yes, that slick, gorgeous Pro Stock scoop was found to add no additional drag to the car. THAT is a win-win-win of epic proportions. A) intake tract pressurization B) sexy as heck C) no drag or any other penalty. Now, due to the extreme volume of air gobbled by the twin Dominators at the start line coupled with ZERO forward speed, they had to size the front opening of the scoop to offer little to no impedance to the progress of that air from the outside world to the carb throats. I am guessing that the opening is about the equivalent of a 9" circle. That yields 63 square inches of size. At a combined (theoretical) 2000 cfm of air intake, which is 2,556,000 cubic inches per minute, or 42,600 cubic inches per second, this yields an at-the-scoop-mouth air velocity of 669 inches per second, or 55 mph. This is all theoretical, of course, as I do NOT know the dimensions of the Pro Stock scoops of years ago. But, supposing this is all accurate, the Pro Stockers hit positive air pressure at the scoop mouth at 55mph. They obviously know what they are doing, as they do spend a long time in the wind tunnels. As I said, though, I do not know what all is going on with those cars, including ACTUAL cfm of the airflow into the engine, etc. I was just taking a guess of 1.4 cfm/hp OR SO. But, if these cars top 200mph, then, at the end of the race, that mouth of that scoop is enjoying 1.4 PSI of ram air supercharging at no expense of horsepower or drag and 0.375PSI at 100mph or so. Shall we shoot for a 55mph top speed at the intake of our cars, too? Or should we shoot lower to take better advantage of the speeds most likely to be experienced on the street. Maybe 27.5mph? If our cars use around 1000 cfm, then that would require a similarly-large 9" round opening. There is no such thing as too much air ram. The throttle body can keep out all we don't need.
