MidnightDriver - if I may make a suggestion, go with upgrades that you can build upon. Power Adders Heads, Cam, Intake Manifold, gears, headers and tunes are the real performers.
Most bolt-ons are offer nothing on stock engines but bling and bragging. Despite what many people say, the 2V 4.6 has a lot of really good engineering in it and two areas where there is no significant improvement to be had at stock levels are the entire intake tract and downstream of the exhaust crossover. Nickel and dime bolt-ons are doing nothing but nickel and dime-ing you and giving little in the way of performance. Until you are making serious power, they are mostly a waste of time and an even larger waste of money. Remember, every manufacturer is trying to sell you something. No matter what they sell, or how good or bad their product is, they need your money to continue their business. There are companies out there that tell outright lies and manipulate data to their benefit to ensure they get your money....they have certainly received a lot of mine. Please beware. I offer below a list of things that have worked, and not so worked. These are my opinions. I am not trying to offend anyone.
The little stuff - very little offered in stock applications, everything combined will not add up to even one of the items listed on the GOOD stuff.
CAI - can actually throw off your tune, causing loss of fuel economy and improper metering by causing noise in the MAF signal. Up to about 350 hp it is not going to be a significant restriction. Any performance gain you see can probably be attributed to the product screwing up the metering of the air resulting in a lean condition.
Throttle body - will give you seat of the pants feel. Everybody says I can feel it all though the pedal. That is because it is physically allowing more air for a given pedal position. It is not an restriction compared to other parts of your engine at stock levels. In fact most people see a reduction in peak torque. The stock 70mm is not going to be a significant restriction until you get within 10% of it's max flow, which is roughly 475CFM. The same applies to the entire intake tract.
Ignition - until you get a supercharger or are spinning past 7500 rpm, you will probably not see any real gain either in coil packs, COP's or control boxes.
Hi Flow air filter - get it if you want but don't expect it to give you much of anything initially. Past 300hp it starts to pay off for the purchase price.
MAF - not a restriction as it is physially larger than the TB, which is also not a restriction at stock levels. Do not get one until you actually are maxing out the stock meter. you will max out the meter voltage long before it becomes a physical restriction.
Mufflers - get a set you like the sound of, beyond that....well thats really about it until 400hp
Now the good stuff....
Power Adders - Superchargers, turbo chargers, and nitrous all offer great dollar to horsepower value...the downside is there is a large minimum to buy. Systems are pricey, but oh so worth the price. Power adders offer offer no real reduction in overall physical air restrictions, but either mechanically or chemically increase the amount of O2 entering the engine. Having a built bottom end will cost a lot but will give you longevity at higher than kit boost levels.
Heads - Single largest restriction in your engine. Get a set of Trick Flows, ported PI, or ported SVO's. The Trick flows offer about a 100hp increase. The others can add a significant level of power as well. A good set of heads will make the most of every other part you put on your car.
Cams - A good set of stage 2 cams will give you between 45 and 60 peak hp with even more for any given rpm after the power peak. A stage one set can improve performance throughout the RPM range on a stock car. A radical set can be the crowning piece of a fire-breathing monster.
Gears - They don't actually give you power but they change the overall torque multiplication of your engine in every gear and put into your powerband faster. At $150-250, nothing, and I mean nothing, will match the bang for the buy-in of a set of gears. On the downside, aggressive sets can cost you a little fuel economy.
Exhaust - Tuned Length Long tubes only, shorties get you virtually nothing. The exhaust manifold is not a physical flow restriction in most cases, the additional power and torque comes from effective exhaust scavenging. Some mid length sets achieve promote some scavenging.
Intake manifold - An upper plenum will get 10-12hp and is a decent dollar to hp purchase. I used to use Accufab but any are an improvement over stock. An entire manifold will give you better high rpm power. The pi stocker is actually pretty good and until you are forced aspiration, it only loses out past 6k to a couple of others. typhoon and the dorman (an OE replacement)are complete junk. Obviously the Bullit and SVO are an improvement, as is the Trick flow which is actually based on them and offers matched runners. Despite a lot of hear-say, the P-51 is a good choice for applications that it is specifically designed for. Despite the genuine gains you will see, naturally aspirated, the price of a complete manifold does not justify the power you get. Until you are doing a max NA effort or have a power adder (especially nitrous since most are aluminum), your money is better spent elsewhere.
Hopefully this information can help you make the most of the resources you have available. I hope I don't offend anyone, that is certainly not my intention. I only offer these opinions out of my own experience, based on mistakes myself or my friends have made.
