The purpose Perrin manifold headers serve is to increase exhaust performance. Most WRX/STI owners at one point or another look to give their turbo setup extra power. The factory configuration works but is not designed for the racetrack. Perrin manifold headers offer an efficient way to shuffle exhaust gases out, giving turbo engines a higher ceiling for potential horsepower. It is an upgrade that you used to mainly see on STI models, but WRX drivers are eligible for this part, as well. Perrin manifold headers also come in a “big tube” format, which offers wider diameter piping for added airflow.
The shape and design plays a big role in how it is effective. These are equal length headers, so there is no deviation in tubing on either side. This is for overall balance. Equal length headers connect to either a stock or aftermarket up pipe and turbo to offer smoother exhaust airflow. In turn, turbo spooling is quicker and boost is improved. In addition, equal length headers produce a more “revvy” exhaust tone. This is due to the airflow being spread out more evenly. It is not an overly aggressive sound, but it is distinctive.
Equal length headers are made with 1.5” diameter tubing to offer a higher rate of exhaust flow. The standard design is intended for WRX/STI models that top out at 400 WHP. Going with the big tube headers means even more power. The main difference here is the wider diameter. The big tube headers measure at 1.625” to open up even more airflow. However, this is not ideal on all vehicles. Perrin makes the big tube headers primarily for Subaru models with large turbos. Check your specifications before ordering.
Like most of their exhaust products, Perrin headers are made of stainless steel. To accommodate the higher flowing unit, the flanges are machined and ported for less turbulence and interference. This part takes up the space used by the 2.5L oil pan in order to initiate more exhaust flow. Due to this design, there is a fitment issue on some models. A 2.5L oil pan will have to be purchased in order for the Subaru steel header to fit on 2002-05 WRX versions.