WRX STi Intakes

PRE-ANALYSIS INFORMATION PRIMER

Jumping right into it, we are well aware of the ECU's tendency to compensate for changes in air f ow; to that end, our installers reset the ECU before and after each test run; without running a standalone engine management unit, this was the only way to gain some sort of consistency between runs.

Additionally, several tuners familiar with the STi platform reminded us of the fact that the particular design of an intake can affect the volume, speed, and angle at which the incoming charge air hits the MAF sensor, causing erratic readings and, occasionally, check engine light conditions. While this is definitely something to consider when reviewing the dyno graphs, also bear in mind that the graphs used to represent the power changes in this LAB section are actual dyno runs, albeit the ones most representative (meaning repeatable) of the samples taken for each particular intake.

Testing both "short" style and "cold air" style intakes in this test begs the question, "Which is more effective at producing power?" Again, keep in mind that specific intake pipe diameters, routing paths, and in- filter accelerators tend to cause erratic turbulence in this particular application which, as we've already mentioned, often throws the MAF sensor and ECU for a loop, so to speak. Therefore, these tests cannot be the sole indicator of which type of intake performs better.

In addition to the MAF problem, other factors - such as intake diameter and filter element type - will affect the power readings. (A true "cold air" versus "short ram" intake test would keep all other factors the same, changing only the placement of - and subsequently the length of pipe leading to - the air filter.) Finally, it should be noted that another run with the stock airbox in place but with the OE filter element removed netted a gain in low-mid end power but a severe loss in top-end (post 5000rpm) power.

SHORT TYPES:

APEXi, Blitz, HKS Each of these setups were as quick and simple to fit as they appear. Simply remove the factory unit and corresponding lines, install the new units and brackets, and reattach the lines. As the integration point from OE to aftermarket intake is similar in all three of these intakes, their performance was expected to differ only by the ability of each of the filter elements to allow air to pass through.

BOX TYPES:

ARC, K&N Like the short ram style intakes, the box types were also particularly easy to install, with just a minimal extra effort to align the enclosure unit. Some might argue that the K&N unit is not a true box type, but if installed properly, the hood liner should form an effective seal with the K&N's shield walls, creating a barrier, while open on one end, should be see enough incoming air pressure to create a "virtual" enclosure.

COLD AIR TYPES:

Fujita, Injen These intakes also weren't particularly difficult to install. By simply popping off the lower splash shield and the fog light cover/panel, it was easy to access the end of the intake pipe to attach the filter and hose clamp. A ratcheting socket and a long reach extension should do the trick.