As Subaru continues to flex its Boxer-derived muscle in the  import scene, the fourth-generation WRX STI continues to dominate both the rally and street arenas. Posted on ” target=”_blank”>Engineering Explained, we dive into the 2015 Subaru WRX STI and how it performs with a COBB Stage 1 flash tune installed.

There are some key changes that separate the newest model from previous generations. A stiffer chassis, larger front and rear ant-roll bars, and stiff unibody anchors with a stiffer track-tuned, high-performance suspension provide even more precise handling and 0.96g of acceleration to the highly nimble WRX STI.

The turbocharged EJ257 2.5 liter boxer engine with dual AVCS, and its 305 horsepower and 290 lb-ft of torque are carry overs from the previous generation. The rev limit was also increased to 7,100 rpm in order to give the car more power at higher rev ranges.

Only one gearbox is available, which is a six-speed manual transmission. The transmission is described as notchy combined with a stiff clutch that requires a considerable amount of effort.

The newest STI has Active Torque Vectoring, which modulates the inside tire to help the car rotate around corners with almost zero body roll and reduced understeer during spirited driving. Not to mention, the tight 13 to 1 steering ratio keeps turning in the hydraulic powered steering system precise and true in the STI as to the WRX that uses a new electric-assisted rack steering configuration.

Before flashing COBB’s Stage 1 tune, the company tested the STI’s 0 to 60 mph on a slight downhill grade, which lasted just 5.53 seconds. Using COBB Access Port Version 3, the STI received a flash tune right from its OBD port, making the upgrade a simple and easy process.

After the Stage 1 flash tune was uploaded, the car was taken out for a run to see if there were any considerable changes. From second gear, they said there was more power and torque, especially in the lower rev range compared to before.

They also noted less turbo lag, which is always a huge thumbs up for the tuning enthusiast. When it came down to the 0 to 60 mph test, the WRX STI did not disappoint.

With COBB’s Stage 1 flash tune, the STI was now pulling 0 to 60 mph in just 5.07 seconds. Being .43 seconds faster after just the first ECU flash, we are wondering how much better the STI can get with subsequent stages added on.

A joy to drive by any means, Subaru’s latest iteration of the WRX STI does not disappoint and will meet the apex of any tuner’s turn with speed and aggression. To say the least, the WRX STI may have gone through being a hot hatch and back, but we can’t argue with the results. Combining power and handling into one package is no easy task and the WRX STI is truly a driver’s car, one to tear up in the canyon roads and open country.

To see if there is a flash tune kit for your Subaru, visit the COBB Tuning website here to view all their available applications. Subaru’s WRX STI is no stranger to the import scene and with the car’s handling improving each model year, it is no wonder as to why the Impreza and its boxer engine dominate the rally motorsports world.