2002-2009 Subaru Impreza WRX / STi (02-05 WRX requires STi oil pan)
Reaching back to lessons learned by tuners in Perrin's past, PERRIN has grabbed a dramatic power increase that was previously bottled up by the factory manifolds. Whether normally aspirated or turbocharged, proper exhaust gas scavenging is vastly important. The turbocharger relies on energy from the exhaust flow to rotate its blades. By freeing up energy that was otherwise restricted by the factory manifold, you can transfer that to the turbo to decrease spool up times and improve power. Perrin's R&D staff was able to manipulate the length and shape of each runner to allow easy installation and still maintain large power increases.
As shown in the dyno plot, this header makes power in all situations. In the past, headers were a trade-off: Some top end power was gained where some low end power and boost response was lost. Also, the minimal gains made the Cost vs. HP scenario not look so hot. The equal length design of the PERRIN header, gives you the best of both worlds. Tons of low end power gained and still the top end power. They find a minimum of 30Ft-lbs of torque gained at lower RPM, and around 15ft-lbs everywhere else. Same goes for Wheel HP: roughly 30 WHP at lower RPM, and about 15 AWHP every where else. Talk about the Cost vs. HP scenario looking good!
The design of the PERRIN equal length is very different from the rest. You will not find huge oversized tubing here just to make it look cool. You will find properly sized tubing designed for the perfect balance of response and HP for applications beyond 400WHP. All of the 2.5L turbo engines come with an oil pan with a large cutout in the side. This allows for a truly equal length, and free flowing header. Many other headers collect on the passenger side of the engine, and due to space constraints cant be truly equal length without compromising flow, and clearances. Because Perrin uses the added room around the oil pan, they can create a smooth transition of the header primaries to the collectors, and from collectors to the uppipe connection. This is why Perrin's header makes power across the entire RPM band.
A small but important feature to Perrin's header is that it is designed to fit to the factory uppipe. This allows for simple installation to either an OEM uppipe, aftermarket uppipe, and Perrin's rotated turbo kits. This is important because you can upgrade any part of the system when you choose to.
Because of the design of the PERRIN equal length header, boost response is also improved. Most all cars will see about 300RPM quicker spool. This does many good things for the car. More boost at lower RPM equals more torque and more power. At the drag strip you will notice quick 60ft times, 0-60 times will be greatly decrease, and the overall fun factor of the car is greatly improved.
The only downfall with the header is the loss of the Subaru sound. The lumpy, thumpy sound everyone has come to love becomes a nice smooth buttery sound, for everyone to fall in love with all over again. Because of the unequal nature of the OEM header, the exhaust pulses are paired together causing that lump sound. The PERRIN header changes the note of the exhaust because of it equal length design. The sound pulses from the exhaust are equalized and spread out, causing the smoother, more refined sound coming from the exhaust.
-321 Stainless Tubing
-Equal Length Runners for each cylinder
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