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Series: 2015+ Subaru WRX Modification (Pt.6 - Cat-Back Exhaust / AOS)

March 08, 2021

2015+ Subaru WRX Modification (Pt.6 - Cat-Back Exhaust / AOS)

Series: 2015+ Subaru WRX Modification (Pt.6)

     Hello and welcome to my Op-Ed on the 2015+ Subaru WRX! This is part 6 of a 10 part series that plans to encompass all of the information you will need to make informed decisions regarding the best upgrade path for your vehicle.

     This week, I will be giving an in-depth overview of Cat-Back Exhausts and Air-Oil Separators. This overview will consider the purpose of each component, how to account for it in a calibration file, as well as what specific brands I recommend.


     The statements made in the article below are subjective and based on my knowledge and experience gained from working with the VA WRX platform.  Please refer to your preferred tuner, or a trusted vendor, for recommendations on your specific set up.


     This Op-Ed is intended to help the user better understand how certain modifications affect the engine and performance, what tuning changes are necessary to account for these modifications, and what brand(s) I recommend for each modification category. This is NOT intended to be a tuning guide. I am NOT an expert in ANY category that will be discussed.


Modifications and Preferred Brands

Cat-Back Exhaust / Muffler Deletes

     Post catalyst exhaust components simply alter the sound characteristics of the exhaust as well as remove excess weight. However, a more free-flowing midpipe my net some positive throttle response as well. The OEM cat-back exhaust includes a non-resonated midpipe and two mufflers.

     Since post catalyst components do not have a noticeable effect on performance, the only considerations would be your own audible and visual approval as well as weight savings. However, it doesn’t hurt to stick with a name brand so as to preserve build quality, material choice, and fitment.

     Installing a CBE (Cat-Back Exhaust) or muffler deletes requires no general tuning changes.

     For post catalyst exhaust components, I’d recommend whatever fits your budget, look, sound preference, and desired weight. For dual exit, I prefer the Invidia Q300 or R400 depending on how aggressive of a sound you’re looking to achieve. For single exit, I prefer any system from Carven. Carven is made in the USA and offers superior weld quality and fitment when compared to other brands.

15+ WRX Catbacks 


Air Oil Separator

     An AOS (Air-Oil Separator) or catch cans serve the purpose of keeping blow-by and oil out of the intake tract and engine. As a result, installing one can help prevent carbon buildup, exhaust smoke, and detonation. It’s one of the most helpful supporting modifications out there for the FA20DIT and highly recommended by tuners and engine builders alike.

     Some key considerations to make when sourcing an AOS are as follows. Is a maintenance free experience important? Then an AOS is preferred over catch cans. What are the power goals? That will determine what type of AOS to install.

     For any type of recirculating AOS, there will be no tune required. This is because the factory PCV (Positive Crankcase Ventilation) functionality is retained. For any VTA (Vent To Atmosphere) AOS, tuning changes may be required to account for changes made to the PCV system. In either case, it is best to discuss the available options with your preferred tuner.

     For an AOS, I’d recommend the IAG street series unit for any engine build below 600 hp. For anything over 600 hp, I’d recommend the IAG competition series unit. This is per IAG and not based on personal preference. For catch cans, I’d recommend the Radium unit. It seems to be the most consistent and the most effective overall at keeping oil and vapors out of the intake and engine.

IAG V3 Street Series Air Oil Separator Black - 15-20 WRX 

IAG V3 Competition Series Air Oil Separator Black - 15-20 WRX 


     Tune in next week (03-15-2021 @ 12:00 EST) where I will be giving an in-depth overview of Powertrain / Drivetrain Bracing, Suspension, and Braking Upgrades. This overview will consider the purpose of each component as well as what specific brands I recommend.