Responsible Modding

This last weekend I embarked on what was both an excellent learning experience, as well as, doing something I should have done a long time ago. I installed a Cobb AOS (Air Oil Separator) on my 2019 Wrx.

As a preface to those unfamiliar with air oil separators or the VA chassis WRX platform, I will take a second to explain why I chose this mod and why I should have done it sooner. The VA chassis (2015-2021) have Subaru’s DIT 2.0 liter flat-four known as the FA20. These engines were, upon release and still today, a step in the right direction for Subaru. It is not perfect by any means, which we will get into shortly, but it solved some issues plaguing previous models. One of the most significant issues that the FA20 faces commonly is excessive oil blow by partly due to the nature of turbo engines, flat-fours, and the poor PCV system. While there is of course, no way to deal with the engine being flat, or the high pressure from the turbo, you can enhance the PCV system. There are two ways to accomplish this goal. The first and most common in other vehicles is a catch can system. This essentially taps into the crankcase vent ports and catches the oil that has blown by. Storing in cans that can be emptied as needed. The other option is the air oil separator. This serves the same purpose but, with the added bonus of recycling that oil back into the system. This means no empty of the can is required. A catch-can system or AOS are beneficial because they can help prevent excessive early carbon build up which can reduce performance and cause damage if left unchecked. Because of the particularly poor PCV in the VA chassis WRX this really should be one of, if not the first, mod you make to the car.

I, like many others I imagine, did not start with this as my first mod. I opted for things that were more fun, and could help in some ways mitigate the extreme heat that we get in Texas. I added a cold air intake, a front mount intercooler, a new electronic boost controller, I got an E30 tune. All things to try and make the block and air entering it as cold as possible. And I finally decided to do what I should have from the start and install an AOS.

One of the reasons I’m making this post is both to explain to those who are new to the platform or maybe just curious, a bit about Air oil separators. And to describe my experience during the install. I am not a mechanic. I am a service writer and I do know a fair amount about how cars work but, I haven’t done too much wrenching myself. Mostly just simple stuff like fluid exchanges, exhaust work, wheels, intakes, etc. So this project was one of the most complex/difficult I have ever undertaken alone. And to be honest, it really wasn’t that bad. It took me roughly 5 hours from start to finish. Most of that time was spent fiddling with hose clamps. And triple checking to make sure I was running hoses to the proper spots. I felt really satisfied when I was done. I wish I would have done it sooner because it’s not that expensive, it can really help the car, and it was a great learning experience. I would highly recommend this mod to anyone with a forced induction vehicle but, more especially a Subaru.