2011 Subaru Impreza STI GVB Part 1

Subaru’s third-generation STI platform was released in the model year 2008 but was initially available only in the 5-door wagon configuration. This lack of choices had many Subaru enthusiasts holding off on purchases until the release of the GVB-coded sedan in 2011. With a few minor facelift and aero enhancements, the 2011-and-up STI models retained the same 2.5-liter EJ257 turbocharged boxer engine with its factory-rated 305 HP power output. The only notable difference between Gen 3A and Gen 3B STIs, outside of the availability of both the sedan and wagon platforms, was Subaru’s switch to a full-synthetic engine oil straight from the factory.

Text by Arnold Eugenio // Photos by Richard Fong // Dyno Testing and Tuning by Crawford Performance

DSPORT Issue #117


The Parts

test-tune-subaru-sti-117-004Our 2011 STI was delivered with just over 10,000 miles on the odometer. As the car was purchased used, the quality and frequency of oil changes was questionable at best. With this in mind, we opted to bring the car up to a full “stage zero” specification that would ensure the EJ257 would endure the forthcoming parts. While the factory spec oil is already a synthetic blend, Royal Purple’s XPR includes higher-levels of anti-friction chemicals and moderate detergents making it suitable for both race motors and street-only engines with a standard (non-high-mileage) replacement interval. Royal Purple’s Extended Life oil filters are claimed to have 99-percent filtration efficiency down to 25 microns with its synthetic micro-glass filtration media.


test-tune-subaru-sti-117-007Though it may seem like overkill to replace spark plugs on a stock engine with 10,000 miles, we opted to take the advice of Subaru specialists Crawford Performance and take the factory iridium spark plugs one step colder. “When you are making more power, the plug will need to be stepped down to a colder plug to avoid pre-detonation under higher loads. (The predetonation) would occur as the plug becomes too hot and sparks too early,” remarks Crawford’s Bill Knose. Under that advice, we opted for a set of NGK LFR7AIX iridium spark plugs.


test-tune-subaru-sti-117-008Factory fuel and ignition timing maps may make concessions for a wide variety of driving conditions, climates and instances of poor quality gasoline. In order to extract the full power potential from each upgrade and bolt-on part, we opted to install and utilize COBB Tuning’s AccessPORT early in the project. The popular plug-in engine management system allows for fine-tuning and complete overhaul of the factory fuel and ignition maps while offering additional control over other functions such as factory boost solenoid control, launch control and flat-foot shifting.

test-tune-subaru-sti-117-005As a preventative measure, we also chose to install a Crawford Performance Oil/Air Separator (OAS). While not typically a power-producing piece, we wanted to ensure the EJ257’s longevity and ability to withstand the upcoming full-throttle dyno pulls.


Turbocharged engines have a tendency to suffer from oil blow-by at earlier stages in their operating life. This is due to the increased cylinder head pressures under boost. While emissions laws require the recapture of the oil-soaked vapors, the constant and gradual build-up of contaminated oil in the intake tract where it re-enters the combustion cycle can lead to decreased performance, gasoline fouling, pre-ignition and pre-detonation. An air oil separator literally separates the contaminated oil from the vapors, allowing the gasses to cycle through the combustion process again. Air/oil separators can either collect the oil for disposal (as in an oil catch can) or return the collected oil to the oiling system like Crawford Performance’s unit.