Soon after Impreza drivers leave the dealer they are already planning ways to customize their exhaust system. This usually involves going with a Perrin downpipe to replace the stock unit.
Turbo Subaru models come off the line with a naturally restrictive exhaust system. They only thing “turbo” about them is the presence of the part itself. But the tubing used in various locations is either undersized or narrow. That is mainly due to that these cars are not intended to be raced in sanctioned competition, but rather, as street vehicles. Installing a Perrin downpipe is often one of the very first upgrades made to an Impreza because of its immediate effectiveness.
It is predicated upon how exhaust works. The denser it is, the more it can maintain adequate speed and temperature when being distributed. A bone stock pipe is narrow inside the tubing, which elicits a choking effect on exhaust. The airflow cannot move through it freely, holding up its ability to exit. Because of this, performance is greatly hindered. Your car is missing out on opportunities to boost up. Throwing in a Perrin downpipe goes a long way towards improving acceleration and boost without making any other major additions to your exhaust format. It is also a crucial step for Impreza owners looking to engage in a full stage 2 exhaust system.
The key is getting rid of the restrictive influence. A Perrin downpipe does this due to the design of the tubing. Rather than portray a slim passageway for exhaust to clear through, instead there is a wide 3” diameter. That is a substantial increase in tubing size over the OEM. Thanks to the increase in room, exhaust is able to roam through the pipe at a higher velocity. It initiates a chain reaction that brings about more performance. Exhaust clears out quicker, giving the engine a little more “breathing room.” In addition, turbo spools in a heightened manner. For motorists who compete on the track it is a necessary improvement over the factory setup.
A main point of interest is always centered on how much of a performance increase a Perrin downpipe is responsible for. It can be difficult to generalize numbers due to certain circumstances. If a car is outfitted with numerous STI exhaust parts, the difference can be quite substantial. However, on a model that has yet to see other upgrades, it may not be as high. Perrin has conducted many dynamometer tests to conclude just how productive their downpipes are. The most common approximation is that you can expect an additional 15-25 added horses after installation.
One thing to take note of is legality. Adding a Perrin downpipe is against emissions control guidelines in most states. The reason for this has to do with the replacement of the OEM catalytic converters, which are responsible for filtering out exhaust gases. Whenever you take the cats out of a car you are essentially making your car “street illegal.” Because of this, a Perrin downpipe is manufactured solely for competitive or off-road usage. When used on residential streets drivers can be subjected to fines and/or failing motor vehicle inspection. Any other Subaru racing pipes that take away OEM catalytic converters also fall under this category.
When searching around for exhaust parts, stainless steel is the material preferred by most drivers. It is both strong and resistant to the consistently hot environment Perrin downpipes are subjected to. Other substances such as aluminum or even iron, to a degree, rust and radiate excessive heat. Perrin uses both T-304 stainless steel in the construction of their Subaru racing pipes. In order to make the precise bends the tubing needs, each part is placed in a mandrel-bender that is digitally gauged to create the appropriate angle for maximum airflow. It aids in maintaining structural integrity at the bend, as well.
Another benefit that comes with these down pipes is the 1/2” flanges. These are the endpoints that connect to other parts such as the turbo. Perrin specializes in giving their Subaru racing pipes very thick flanges in order to prevent cracking or fracturing due to stress at the ends. It is also important to stave off any exhaust leaks that can occur.