Intakes, Ram Pods, & Filters
Feeding the Flame
The next step for improved airflow is replacing the factory air filter with either a high flow filter or a cold air intake. Most cold air/Short ram intakes utilize a high flow cone filter. The idea behind both is that you are giving the engine the ability to suck in cold air from the fender well as well as a greater volume of air.
A cold air intake (which takes its air usually from a fender well) tries to feed the engine with colder or denser air. Once again, properly tuned (read with some sort of engine management), an intake is worth 9-15 hp. Without engine management, your intake will give 0-12 hp.
A side benefit of a cold air intake is that great "sucking" or gulping sound the engine makes when you get on the gas. There is a big debate on Cold air intakes on Subaru?s, saying that they aren?t good for them. This is true, but only if you are not running any engine management. If you don?t have any engine management then it would be a wise decision to hold off on this until you have some sort of engine management in line.
Another thing you want to be careful with if you a re running a CIA (Cold Air Intake) is going through puddles. With the air filter down in the fender well, you are more likely to suck in water if you were to go through a big puddle. If this does happen, it will prove to be disastrous as you will hydro-lock the engine which equals expensive repairs. See the picture of the APS Cold Air Intake above.
A Short ram intake (also known as a ram pod) is a shorter version of a Cold air intake. Where the CAI draws air in from the fender well, a short ram intake draws air in from the engine bay. Like the Cold air intake, there are good and bad things about a Short ram intake. On the positive side, there is a shorter distance for the air to travel into your engine, you are less likely to suck in water, and they are almost always cheaper. On the Negative side, since you are sucking in air from inside the engine bay, you are drawing in HOT air. This can lead to problems if under hood temperatures get too hot. The engine has to work harder to keep itself cool and it makes it easier to over heat. See the Cobb Short Ram Intake Picture above.
One thing I do want to add when it comes to intakes is, be weary of intakes that are just a cone filter on the end of a tube or piece of pipe. It is important that unless you are taking the car to a tuner who will tune for the intake, that you find an intake that is the same inside diameter as the stock box (65mm). Also it is good to look for an intake that has a velocity stack. Cobb?s intake uses a velocity stack that smoothens out airflow as its being sucked in to the turbo/engine. This helps reduce the amount of turbulence flowing inside and past the Mass Air Flow Sensor. If there is too much turbulence, it will disrupt the readings and can trigger a check engine light. It can also make your car run ?lean? as the ECU is not able to accurately read the amount of air being sucked in. It can also cause your car to idle rough and in turn make your car run like crap.
One of the best things to do is add a ?High Flow Panel filter? (K&N, Perrin) that goes inside your stock box. These filters are usually re-usable and are less restrictive than ordinary ?paper? filters. They are great because the will add horsepower, do not require tuning, and can be cleaned with a special kit that is inexpensive. The factory box will also flow enough air to handle 375+ hp.
When you upgrade the turbo, you will need a tune after it?s installed, and will then be able to get more use out of an aftermarket intake. A cheap alternative to a cold air intake (that works very well, I might add) is to perform a "resonator-ectomy" combined with a K&N or Perrin High Flow Filter. Below Left: K&N High flow Panel Filter. Below Right: Perrin Panel Filter.