The stock air-box is very restrictive and does not provide the necessary airflow that a high performance engine requires to run at optimum efficiency. To resolve this issue, several alternatives to stock are available. When any of these modifications are performed, the stock Blow-Off Valve can usually be heard from within the cabin of the car and somewhat increases the amount of background noise. Expected gains can be between zero (0) and fifteen (15) horsepower.
This is a drop-in replacement for the factory filter and uses the factory air-box. The filter is far superior to the stock filter and is made of the same material as the FIPK, however alone, this is not a very effective solution. If this is the upgrade path you choose, consider combining this with the Cut Air Box modification (see below).
K&N Filtercharger Injection Performance Kit (FIPK)
Perhaps the most popular of all air filter upgrades, the FIPK allows removal of the factory air-box completely and instead replaces it with a oval conical open-element air filter which allows far better flow than the stock design, and in addition to filtering the air, also assists in smoothing it as well. This filter claims to last 50,000 miles and is then washable and reusable with K&N Recharger Filter Care Service Kit. More realistically, the K&N air filters should be cleaned approximately every 25,000 miles or whenever the inside of them has turned mostly gray.
This is more or less a K&N FIPK, with a bigger filter element, allowing more air flow. It usually also costs less because it does not have California Air Resource Board approval and is for off-road use only. This should not effect emissions any more than a FIPK would because it is almost the same kit. This kit was designed for the second generation Eclipse/Talon (95-98) but fits the 3000GT / Stealth.
This K&N manufactured filter features a dual cone open element design. It is available in a wide variety of colors. The top of the cone is open rather than closed off as in the K&N. The open top, in theory, provides greater surface area and therefore superior airflow, however there is no hard numbers to support this claim.
HKS Super Power Flow
This aftermarket open-element air filter also replaces the factory air-box, but instead of being cone shaped, is shaped like the top of a mushroom. It is made of foam, and is available in two variants. The first variant is the direct competitor to the K&N FIPK and performs the same function; the second variant is designed to work with the HKS Vein Pressure Converter (VPC), contains two filtering "mushrooms", and in addition to replacing the factory air-box also replaces the Mass-Airflow Sensor, which is another restrictive part of the intake system. The second variant will not work without the VPC. This filter element is not washable and should be replaced every 6000 miles.
The stock y-pipe (the pipe that connects the two intercooler pipes to the throttle body) is notorious for blowing off at boost pressures around 15 PSI and above. The nature of the gasket in the y-pipe precludes any effect tightening the clamp may have, in other words, the stock y-pipe was simply not designed to withstand high boost.
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