Intake There are basicly two different types of intakes on the market. "Short Ram" and "Cold Air" intakes.
A "Short Ram" intake is a filter on the end of the intake tube that sits inside the engine bay. Generally a shorter distance from the filter into the throttle body.
A "Cold Air" intake locates the air filter outside of the engine bay. It gets its name "Cold Air" from pulling in air from out side of the engine bay not the warm air from inside of the engine bay. Cold Airs do not magically cool off the air, it just brings in cooler air from outside the engine room.
Intakes that fall under the "Short Ram" catagory are: Jim Wolf Technology (JWT) Pop Charger, K&N Typhoon and Fujita intakes.
Intakes that fall under the "Cold Air Intake" catagory are: NISMO, AEM and INJEN.
There are some more intakes then these, but these are the main ones to look for.
The Performance Difference
All of these intakes will give you some kind of gain when installed properly. They all give you a larger more roaring sound from the engine bay at full throttle once above around 4000RPM. With a Short Ram Intake, there is less distance for air to travel from filter to throttle body. This makes for better throttle response and greater power at higher RPM's. Cold Airs do not have as quick of a throttle response but gain a little more in the mid range of the RPM band.
Air is constantly moving through the engine bay while the car is in motion. Filter placement is key here. Where the Short Rams place the filter is in a pressurized zone where air is directed towards the filter. On a Dyno, the car sits still so generally these numbers are lower, but in motion, this is where these intakes shine.
Filter placement is something to look for on cold air intakes. The INJEN intake places its filter infront of the radiator. At highway speeds, a cushin of air is formed around the filter directing on coming air around the filter. It is harder for the engine to draw in air when the filter is in a high turblent area like this. On the NISMO / AEM intake the filter is placed infront of the wheel. In this area air is less turbulent so the engine can draw in air with less effort.
With a Cold Air Intake you can possibly suck water up into your engine. To avoid this, look for an intake that includes or has an option to add a water diverter valve. This keeps water from being sucked into the engine by bringing air in through the valve rather then the soaking wet filter. The NISMO intake includes this. It is an option with the AEM. Short Ram intakes do not have this problem.
Is it possible for an aftermarket intake to void your warranty? Yes. Only if the Mass Air Flow sensor is damaged. The only time this happens is during instalation or if an over oiled filter is installed. If oil or any particle comes in contact with the MAF it could damage it. A MAF can be damaged with the stock intake as well.
The intake that makes the best horsepower gain for the money, sound, and performance that I would recomend is the JWT Pop Charger. $120 plus shipping and a independantly proven consitant 6.5 Horse power to the wheels gain. This is the way to go.
There are many makers of exhaust systems. NISMO, 5Zigen, APEXi, Amuse, ARC, Borla, DC Sports, Fujitsubo, GReddy, HKS, Injen, Invidia, JIC, Magnaflow, Power Enterprise, Stillen, Tanabe and Veilside... (Just to name a few). How do you know what is rite for you?
Cat Back / Y-Pipe Back / Axle Back? Whats the difference?
In the exhaust system of most cars these days, they are structured like this. Exhaust Header, Catalytic Converter, Pipe, Muffler. We have 2 headers off the cylinder heads. 2 Catalytic Converters off each Header. a Y-Pipe that joins the 2 catalytic converters to 1 pipe, a Mid Pipe and finally to the muffler which splits into two tips.
A Cat-Back exhaust system replaces everything from the Cats and back. It does not replace the cats, but from directly behind them.
A Y-Pipe back exhaust replaces everything from the exit of the Y-Pipe.
Axle Back replaces everything from the rear muffler back.
Some Y-Pipe back exhausts are Fujitsubo, JIC, Veilside, Tanabe etc... These exhausts can be used with any Y-Pipes which are also sold seperately.
NISMO, HKS, INJEN, STILLEN, and GReddy make full cat-back exhaust systems. GReddy, HKS, and Stillen's exhaust systems are true dual system where the piping from one side of the exhaust system does not merge with the other (unless a X pipe or H pipe is in place).
JIC, Tanabe, Fujitsubo and NISMO offer Y-Pipes seperately that can be used with any Y-Pipe back exhaust or even used in different combination with any Cat-Back exhaust that uses a Y-Pipe.
Lets look at materials of the exhaust system. Most exhaust systems today are made from Stainless Steel. This material will not corrode from salty air or salt on the roads. Stainless Steel is also very durable and can take abuse. Some exhaust manufacturer's are making systems out of Titanium. Titanium exhaust systems are a fraction of the weight of a stainless steel exhaust but are double or tripple the price. A style for exhaust's is a "Burnt Titanium Tip" which gives a special look to your exhaust system.
Hope this info helps some of you.