The 2008 Subaru STI is already a potent machine straight from the factory, but for true performance enthusiasts seeking to dominate the track, there’s always room for improvement. This journal details the transformation of a 2008 Sti into a dedicated track car, outlining the key modifications and upgrades implemented to maximize its on-track capabilities.
The journey began with addressing the suspension, a critical aspect for any serious track build. The factory struts were swapped out for BC-BR coilovers, offering adjustable ride height and damping for fine-tuning the handling. New Lower Control Arms (LCAs) were installed, along with stiffer Whiteline bushings at the front of the LCAs to minimize unwanted flex and maintain precise suspension geometry under hard cornering. Notably, the upgraded LCAs, identified by their red color and originally introduced by Subaru in 2011, were chosen for their enhanced durability. These were painted red to match the rear adjustable Agency Power arms, ensuring a consistent aesthetic. Seats and harnesses were also installed at this stage, crucial for driver safety and stability during high-G maneuvers on the track.
Engine performance was next on the list. “TGV deletes” were performed on the injector bodies to remove intake obstructions and smooth out airflow, optimizing engine breathing. The passages were meticulously matched to the manifold and heads for seamless flow. A Moroso aluminum oil pan was installed, providing increased oil capacity and improved oil control under track conditions, paired with stiffer motor mounts to minimize engine movement during aggressive driving. Installing the motor mounts proved to be a challenging task due to limited space. An oil filter bypass block was also attached, preparing for the enhanced oil cooling system.
To combat the high oil temperatures common in track driving, a substantial NOS Setrab oil cooler was sourced. This oversized cooler, measuring approximately 12x12x2 inches with 40 rows, offers significant cooling capacity. An Accusump, a pressurized oil reservoir, was integrated to provide supplemental oil pressure during demanding track sessions, safeguarding the engine against oil starvation in high-G corners. Fuel delivery was also addressed with a new, higher volume Walbro 255 fuel pump to ensure adequate fuel supply for increased power levels. An adapter kit was ordered to accommodate the Tial Blow-Off Valve to the front mount intercooler (FMIC).
Further engine enhancements built upon previous modifications. The heads and manifolds were ported and blueprinted, incorporating a racing valve job and radiused exhaust seats for optimized flow. Manley springs and titanium retainers were installed for improved valve train stability at high RPMs. A Blouch Dominator 2.5 XT-R turbocharger, featuring a 3″ air inlet and 8cm turbine A/R, was selected for its balanced performance. Injector Dynamics 1000cc injectors and an upgraded Walbro 450 fuel pump, along with an Aeromotive 13109 A1000-6 Injected Bypass Regulator, ensured sufficient fuel for the new turbo. An Agency Power 3″ polished aluminum hard turbo inlet and a KS Tech MegaMAF 73mm Big MAF Cold Air Intake were added to maximize airflow. A Turbo XS type FMIC and Grimmspeed EBCS were utilized for efficient boost control and cooling. NGK Iridium IX Spark Plugs, one step colder than stock STi plugs (LFR7AIX # 2309), were chosen to handle the increased heat.
The Setrab 40-row oil cooler was paired with a Mocal OT2 176°F thermostat bypass valve for optimal oil temperature control. A Canton 90-degree rotating remote oil filter adapter and remote oil filter mount were installed, using Ford-style filters like the K&N HP 3001. Mocal “Titanium” line AN hose ends and Racelight -10 AN hose were used throughout the oil system. The OEM oil heat exchanger was removed and replaced with a Subaru oil filter union (part # 15018aa050, superseded by 15018AA090) in conjunction with the Canton remote oil filter adapter. The Accusump was retained, and the Moroso aluminum pan was upgraded to a KillerB pan, windage tray, and pickup tube for superior oil management. A Crawford A/OS (Air/Oil Separator) replaced the Moroso unit, venting into a JEGS breather-catch tank. The Perrin crank pulley was upgraded to a Fluidamper. The TGV delete modification and port matching were also performed.
Initial track testing with the stock engine and EFI dyno tune revealed a weakness: ringland failure due to oil in the intake caused by an inadequate Moroso A/O separator. This led to the installation of a new OEM short block with CP forged pistons and ported heads with a valve job by Kiwi Engineering. This revised engine configuration produced 395WHP/391FPT on EFI’s dyno and briefly handled 26+ PSI of boost. All evap/emissions components were removed, and a fuel line loop with a check valve was implemented for fuel tank venting. A roll cage was installed for safety, and modifications to the front end were made to accommodate the Setrab oil cooler. The vapor collection system was removed in favor of a vent hose loop leading to the roof with a check valve. SPA Technique dual/digital gauges were installed to monitor vital parameters such as oil pressure, oil temperature, water temperature, and boost, providing crucial real-time feedback during track sessions. These modifications transformed the 2008 STI into a formidable and reliable track machine, ready to tackle any circuit.
