So I've got a question, I bought a 04 5.7 hemi, and I've already put a k&n cold air intake and a afe throttle body spacer on it. I'm thinking about putting some more things on it you think you could tell me some things to do to add hp?
The goal of all intake systems is to warm the air. Liquid gasoline doesn't burn or develop any horsepower. It just goes out the exhaust, wasted. Gas has to be in vapor form to burn. Intake systems warm the air to help that occur. Why would you want to defeat that? Cold air intakes trick the Engine Computer into thinking the air is colder, and since it also thinks the fuel won't vaporize as well, just like chokes on carburetors, it is programmed to command more fuel in hopes a big enough percentage vaporizes for the engine to run right. You'll get extra fuel, but you won't get the needed extra air to go with it.
Race engines use cold air intakes because colder air is more dense, so more can be packed into the cylinders, and the carburetors are jetted to provide the matching extra fuel. The only time there is a benefit to this is at wide-open-throttle. At all other throttle settings, you may have the capacity to pack in more air, but you will never be at wide-open-throttle to take advantage of it for more than a few seconds.
Carburetors are different in that respect. They have idle jets and high-speed jets, and those are the only two places they can be fine tuned for a perfect air / fuel mixture. At all other throttle settings, the mixture can't be allowed to dip even slightly into a lean condition because that would cause objectionable hesitations and stumbles on light acceleration. To prevent the chance of that occurring, in that mid-range the mixture has to be sufficiently rich that no matter what happens, it never drops into the lean range. There were no computer controls, so if you packed in a little more air, you could use some of that wasted gas to get a little more horsepower. Also, if necessary, you could change the jets to provide more fuel, but in the end, what you would have gained, the rest of us obtain by simply pressing the accelerator pedal a little further.
With electronic fuel injection, your computer provides the exact perfect mixture at idle and high speed, just like a carburetor, but also at any throttle setting in between and all the way to wide-open-throttle. It's silly to think you're going to improve on that, but once the oxygen sensors warm up, their signals are added to the fuel metering calculations. Those readings result in a very precisely tweaked air / fuel mixture. If you add a cold air intake system, that will just trick the computer into providing more fuel to go with the air and the oxygen sensor readings will keep that mixture perfect at all speeds and engine loads. What you will have gained is a specific amount of power will be developed now at a throttle position that is perhaps " less than before. That is what gives the illusion of more power. The only place there is anything to be gained is at wide-open-throttle, and where are you going to drive like that for more than a few seconds?
Carburetor spacers were used or removed to change the characteristics of throttle response. The design of the intake manifold runners and the passages in the carburetor determined whether an engine was most responsive on the low end, like for motor homes and buses trying to get going at a stop sign, or the high end for racing and police engines. You don't have to worry about that. Your computer looks at throttle position, direction of change, and rate of change as a starting point in calculating the fuel needs. The MAP sensor tells the computer about load on the engine. Coolant and air temperature sensors provide mixture fine tuning data. If your cold air system results in more air, the computer will calculate a higher fuel need based on that colder air temperature, and the oxygen sensor will help insure the mixture stays correct. All of this will happen at a slightly less-open throttle position, that's all. You aren't going to pull a heavier trailer, and you aren't going to go up a hill any faster, unless you do this at a constant wide-open-throttle. The change in the "personality" of an engine, meaning throttle response, power band, etc, won't be noticeable because it's the computer control in charge of that now, not the physics of the intake manifold. You are not likely to improve on what the engineers developed with their computer modeling and many hours of research and development.
You can look into the "chips", or computer boxes that alter sensor readings, but those really work best on diesel engines. The Cummins, in particular, has been so severely detuned for emissions, and to prevent destroying transmissions. The aftermarket controllers take advantage of that to allow those engine to develop more of the horsepower they are capable of. A friend of mine has three, a '99, '06, and a 2012 Megacab, all duallies, and all with these chips. The acceleration and load-pulling capacity are mind-blowing. There's no way to come close with a gas engine unless you're willing to settle for five miles per gallon. The stock transmissions for gas engines won't handle that horsepower either.
Remember too that automotive marketing is an extremely competitive business. If a manufacturer could find one more horsepower, one more cubic foot of cargo room, or one more cup holder to advertise, you can be sure they would do it. If they could find another ten horsepower without adversely affecting emissions, reliability, or fuel mileage, you can be sure they would do it.