Intakes
Written by MB38
There are three main types of intake "upgrades" you can perform:
1: Cold Air Intakes
2: Short Ram Intakes
3: Drop-in Filters
The first thing to note is that Imprezas do not like to have their intake plumbing fiddled with. Many tuners won't allow a car on their dyno if the intake has been modified. The single best change you can make to your intake tract is the removal of the intake silencer.
1: The concept that drives cold air intakes is simple: colder is better. The piping extends from the MAF down into the fender behind the fog lights where it will, in theory, suck in colder air than it would in the engine compartment. While it's a good theory, there is a problem. The ~5-10 degree intake temperature difference that you will get by sucking in fender air will be thoroughly negated by the 400+ degree temperature inside the turbo. In naturally aspirated Imprezas, the colder intake temperature will not yield greater horsepower either. In fact, in both forced induction and naturally aspirated Imprezas, any cold air intake will merely yield a CEL. There has been no dyno proof that cold air intakes have any positive effects on Imprezas.
2: Short ram intakes stem from a different principle than cold air intakes. The short ram intake sucks in the same air that the factory airbox does, it simply does it in a more efficient manner by reducing restriction. In both naturally aspirated and forced induction Imprezas, this lowered restriction will cause a dangerously lean fuel mixture and a CEL. There is only one [WRX] intake on the market (Perrin Performances) that will not yeild a CEL as the MAF housing is the same diameter as stock and the filter element has enough restriction to keep from causing problems. There has been no dyno proof, however, that this intake increases power.
3: Drop in filters rely on the factory airbox to supply air. The filters are lower restriction than the stock filter which, theoretically, increases power. Unfortunately, there has been no dyno proof to illustrate these power increases. Some drop in filters will cause CELs and lean-mixture problems, some will not. There is no advantage to buying a drop in filter over the stock airbox.
There are only two circumstances when an aftermarket intake of any kind will be required or will increase power. The first is when a front mount intercooler has been installed. Because of the way that FMICs are plumbed, the factory airbox must be removed and replaced with a short ram intake. The setup must then be tuned appropriately.
The other condition is on cars making more than 350awhp on a Dyno Dynamics Dyno. Only at these extreme power levels is the factory airbox's utility expended.
In other words, save yourself the money.