There is a statement that I have making, wich is "All intakes are the same". Thats actually a open ended statement. Well, technically yes they are all the same. An AEM intake won't give you any more power than an APC intake would. The differences between them are so minute that the most expensive dyno would have a hard time figuring out the difference. Regardless to what material the intake is made out of, there would be little or no siginificant difference between the two. However, ther are two things that would diferentiate one product from another. That is intake air temperature and air-filter flow rate.
There are also two different types of intakes. You have your short ram or cold air, more commonly reffered to as CAI(Cold Air Induction). Short ram intakes consist of a shorter intake tube, where the air filter component rest near or within close proximity to your engine bay. Now some of you may say, "Why in the hell would you want your intake to suck in dirty, hot air?" Well you don't, and that is why the short ram is the less desireable of the two. The cold air intake is slightly different, as the tube is longer and places the filter component outside or further away from your engine bay. However, this too has is downsides, but I'll get to that later.
So now we have discussed the intakes. You may be wondering, "What about the filter". Well hold your horses. Most stock filters in your car are made of a lighter, looser form of paper than you would find in your printer. It usually consists of many layers of what appears to be a thick tissue paper. The only problem with paper is that, while it allows air to flow freely, it still holds back some of those precious oxygen molecules. However, the paper is cheap and does filter air very thourougly. The next level up are K&N's cotton filters that are soaked in a oil. The K&N's aftermarket filters work better than stock simply because they allow more air-flow and have more surface space. Now you may have squinted when I told you the cotton was soaked in oil. Well its not the oil you are thinking of, its a sticky type of oil that catch smaller particles in the air as it is filtered through the cotton intake cone. The K&N filter is quite efficient and even works better as it gets a moderatley dirtier. However, the cotton cone does allow some tiny particles into the engine.
The intake charge temperature, or temperature of the air entering your intake, has a great effect on power output. Engines make good power when the temperature from the intake greatly differs from the temperature of the exhaust. So if your exhust is coming out at 300 degrees farenheit, and you run your car at the drag strip in the fall and summer... the cooler fall air should give you more horsepower creating a better run. There are many ways of allowing cooler air to reach your intake, taking out head lights, creating cold air boxes, and modifying hoodscoops to directly give ambient air to your engine. Well before you get crazy with it, you should know that one major drawback with CAI systems is that you can suck up water into your engine. This can result in hydrolock.
Hydrolock is where a siffucient ammount of water enters your engine to the point it locks up and stops. If you get a few good squirts of water into your engine through your intake, the cylinder(s) could become dead cylinders and cause your engine to shut down. Theres a good chance you will not suck in enough to water to destroy the engine completley, but in the event that alot of waters enters your engine. The piston(s) would hit a wall of water within your cylinder, not be able to compress the water, the connecting rod would either bend or break and the next revolution of the crankshaft would send the broken rode through your engine block. Permanently damaging a once perfectly good engine.
Now AEM has done os the favor of creating a by-pass valve on intakes. You place this item between your intake tube(yeah you'll have to cut teh intake in half) . It consist of rubber like gasket with foam under it, and when water is sucked in the intake(this creates a pressure drop) the valve on this product opens up and allows air to flow in from the surrounding area while blocking the water from within the intake. After the water flows out of the intake, the pressure returns to normal, and the by-pass valve closes. Cool Eh? Well however cool it may be, the by-pass valve creates turbulence within the intakes airflow thus making a CAI(with a by-pass valve) less or equivalent in power to a short ram intake.
As I mentioned above, people have specially modified hoods that allow air to reach the intake, cut holes in bumpers, or remove headlights. This is what is known as a "Ram-Air" setup. Used for decades by domestic cars, this element on intake has been brought to the imports. The Ram-Air setup places the intake into air flow path of the vehicle creating more air in the filter and cooler intake air.
I have seen many people ask "Why does it matter what "kind" of air my intake breathes in?". Well lets go back to freshman chemistry and phsyics. You should know by now that colder air is far more dense than hot air. The air does'nt matter but the molecules of oxygen within make a difference. When any element is cold, the ammount of molecule movement is reduced and the molecules stay closer and packed together. If the element is hotter, the molecules move arround violently. Now if we have a group of soldiers marching single file line, side by side. They represent oxygen. We have a group of people running in a cluster that also represent oxygen. Now if I had an extremly large vaccum, I would be able to suck up more of the marching soldiers than the running people as they are more dense. Same with air intakes. The colder the air is, the more oxygen occupying a given volume is present. Quite simple huh?
IMPORTANT NOTE: All of your rice ass wantabes. Taking the cone, or filter off your intake will not allow you to take in more air. If you believe this, then you should re-vist your local chemist and phsyics teacher to have them explain to you the relevancy of surface volume. The larger the surface area, the more air your intake will be able to take in at one given intake stroke. So in theory a larger cone, to the point its not so large that you are not able to occupy all of the surface area, will give you better horsepower numbers.
There are probably more sciences that involve intakes than I can explain. This is just a basic guide to get you informed. I'm on my quest to battle ignroance. I hope this helps