Improving The (2002-2007) Subaru WRX/STi Intake

A while ago I posted on Western Subaru Club about the GP Moto elbow and how it affected the STI boost/airflow.

This time I decided to test the stock intake, complete with the resonator, against the modified version that I have been using for the last few years. It replaces the resonator with a “velocity stack”, otherwise also known as subwoofer vent flare.

velocity stack

It can be bought here:

or here:

The stock intake system:
stock intake system

After making some baseline runs with the modified setup, I re-installed the resonator and collected several runs. This was done without taking the car off the dyno. I had intended to test the AEM intake after this but the 3rd gear in my transmission decided to call it quits and killed itself :-\

Install pics
Airbox mod 1

Airbox mod 2

Airbox mod 3
Red is the modified intake, Blue is the stock setup with the resonator.
resonator v velocity stack HP

resonator vs velocity stack boost

AFR was richer by ~2% with the resonator in place and there is a clear reduction in horsepower output above ~5000rpm.

Additional data from 07 STi, May 17th, 2011
2007 STI airbox mod

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