When I bought this car new in 2011, I really had no idea just how far the rabbit hole would go for me. This was my third Subaru, the first being a 2004 WRX and the second being a 2005 STi. The 2004 WRX was a great intro to the platform and a good way to get my feet wet. The 2005 STi was the step up and the plan was to build it up as far as possible but after just 6 months of owning it, it was lost when my wife and I were hit by a drunk driver at a stop light. A suitable GD chassis wasn't available at the time and Subaru had just brought back the STi in sedan form with the 2011 model year so we decided to go ahead and pick one up and start over from there.
Flash forward 6 years, and here we are today, way down the rabbit hole but still far from the bottom. The car evolved from a daily driver, to a balanced setup that was designed to be able to do everything as well as possible, which at the time, meant street use, light track duty and some occasional drag racing. Over the last couple years, the focus has shifted away from street and drag and onto heavier track use. The state of the car is a highly competitive Time Attack car built for the Street Modified class and currently being run in the GridLife Time Attack series.
What I am going to talk about in this post is mainly the current setup on the car and a focus on why it is setup the way it is and how it works well for what I am currently doing with it. To catch up to here, you can read my build thread on NASIOC if you are interested but it isn't up to date so this post will somewhat bridge that gap.
The heart of the car is an Outfront Motorsports closed deck engine that was spec'd out specific for road racing and E85 use. It uses CP 9:1 compression pistons for a small bump which helps add some area under the curve and makes the car more responsive coming back on the throttle. Rod selection was Wossner H beams due to being very strong but exceptionally light compared to other options. The idea was to keep the rotating assembly as light as possible since the car would see a lot of high rpm use on the track. Head stud selection is the custom APR 1/2" offering from Outfront and the bump in size keeps the heads down with the heavy use around the track. The heads were upgraded with +1 valves, springs and GSC S2 cams to suit this application well. This motor was dropped into the car in May of 2014 and is still running strong as ever this season even after 2 and 1/2 seasons of abuse.
The choo choo that moves this things comes from a Borg Warner EFR 8374 turbo. It utilizes the 1.05 a/r twin scroll exhaust housing with twin TiAL 38mm gates on the Full Race Motorsports turbo kit. This turbo was selected specifically for this application because it is big enough (62.6mm inducer) to make some big horsepower numbers when needed but reach the mid to upper 500's with moderate boost levels which keeps things really efficient for track use. The EFR series of turbos were designed for the Indy car series and Borg Warner was asked to completely re-engineer things to be as efficient as possible and that tech really does shine on the track. Despite the large size, this turbo comes alive well under 5000 rpms and has incredible transient response for it's size. What that means on the track is that the is never out of a strong, usable powerband and when coming back on the throttle between gears or corner exits, the power comes back in an instant with little to no discernible lag.