With forced induction, it's a different game because more performance can be gained with intake mods. Typically, a turbocharged motor can see 20-30 HP gain on the dyno with just a cone filter and no other mods. With a charger (turbo or supercharger) the motor is actively seeking more air compared to a NA motor which takes only as much as it displaces. This is why it is crucial to have free flowing intake and exhaust in a FI car in order to maximize the benefits of supercharging.
Think of the motor as an air pump... it's a lot easier to understand and visualize that way. Better yet... simplify and think of it as a single piston/cylinder motor... a basic model super soaker type water gun... or a syringe. Let's say it's a 10 ml syringe. When you pull the plunger/piston back to draw water... if you pull it back at to the 5 ml mark, it'll only draw 5 ml of water. And, if you pull it back all the way to 10 ml, it'll only draw 10 ml of water. What if you want to draw 15 ml? and you only have that one 10 ml syringe? The only way to get more water into that 10 ml chamber is to compress the fluid. So assume you attach the syringe to a pump to force the 10 ml syringe to hold 15 ml of water. With the additional 5 ml of water, the syringe's chamber will become pressurized and the force of the compressed water molecules pushing against one another will force the plunger back... if you don't hold the plunger in place with force, the plunger will be pushed out of the syringe and spill 15 ml of water on to your table or floor (which displaces 15 ml of air). Same thing with a motor... when intake boost is increased... at some point you will have to use stronger forged connecting rods, head studs, and other hardware to keep the motor from blowing apart.
To make more power, you need more air. When you have more air, you have to supply more fuel. When you have more air and fuel, you have to have a hotter spark or you'll get a inefficient combustion and waste gas and not make as much power as you should. Everything is related... it's rare to mod one thing without having to mod something else too. There is no such thing as a cheap bolt-on big power mod. Some people might say you can bolt on some cams and make more power. Well, not really. Cams don't make more power. They just move the power band around along the RPM range. High end, low end, or mid range. If a company claims to make more power all around with their cams... they're lying. Keeping the motor NA, the only way to get more power is to:
1. Stroke and/or bore to get more displacement
2. Increase compression ratio with different pistons
3. Less restrictive exhaust (small gain)
4. Less restrictive intake (small gain)
5. Mess with ignition spark and timing (small gain)
Internal motor work is retty expensive stuff. Supercharging costs about the same (stage 1), if not less... and makes more, if not the same, amount of power. Less labor involved too.
A ram-air type intake could work... but only in accomplishing the task of supplying/surrounding the filter with ambient (or near ambient) temp air. You won't see positive intake pressure from a ram-air intake until you reach speeds of 100 mph or so... a speed our 130 hp (at the wheels) 4,000 pound truck won't see often enough to take advantage of the ram-air effect. Cowl induction, on the other hand, is a much better way to lower engine bay temp and to encourage air flow from outside the engine bay to within. Those body hugging hood scoops you see on a lot of the import body kits (and some OEM muscle car hoods) are for cosmetic purposes only. For hood scoops to function, they have to sit at least 1" to 2" above the body surface. The classic Pontiac GTO, for example, air hits the leading edge/face of the hood and skips right over the scoops. This is why the pro drag funny cars have scoops sitting way high above the hood. It is also the same reason why F1 cars have the intake scoop above the driver's head... just about the highest part of the car.
Ron (vxconcepts.com) is working on a carbon hood insert with a extraction type vent.
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