STI 2006 Recipe for Power

STI 2006 Recipe for Power

August 14, 2023

STI 2006 Recipe for Power

When it comes to building an aggressive street car that commands respect on the road, power is the name of the game. But it’s not just about raw horsepower; the perfect recipe for power involves a delicate balance between performance and drivability. In this blog post, we’ll take a closer look at how the 2006 Subaru STI was transformed into a true powerhouse that leaves no room for doubts.

Power Package

The journey to unleash the true potential of the 2006 Subaru STI began with a formidable FLI Stage 4 power package. The heart of this package is a FP Green (49 lb. Wheel) turbo, working in harmony with a Perrin FMIC, APS 70mm CAI, APS header/up pipe, and APS 3.5-inch turbo-back exhaust. The power delivery is further enhanced with PE 850 cc injectors, a Walbro fuel pump, and a FLI custom factory ECU reflash saved on the Cobb AccessPort.

The initial results showed respectable numbers, with 369 wtq and 331 whp on 91 Octane fuel with 21 psi of boost. However, it was clear that this was just the beginning.

Long Block and Cylinder Heads

The goal was set to achieve a reliable 400 whp and 400 wtq, and to do that, the FLI Stage 3 closed deck short block was paired with FLI Stage 3 Port and Polish heads, housing Cosworth 264-degree camshafts. For improved airflow, Supertech 1mm oversized intake and exhaust valves, along with a FLI valve job, were added. The compression ratio of the long block engine is 8.2:1 using Cosworth 0.78mm head gaskets, ensuring maximum power and durability.

Turbo Kit and Reverse Front Mount Intercooler (RFMIC)

To make way for even more power, a custom Garrett ball bearing GT30 external wastegate setup was crafted by FLI. Additionally, the APS header and APS 3.5-inch turbo were coupled with heavy-duty V-band connectors. To compensate for the increased lag due to larger turbos, FLI rotated the intake manifold and designed custom piping for the reverse front mount intercooler (RFMIC). This RFMIC setup significantly reduced turbo spool time, providing more responsive power delivery.

ECU Upgrade

As the modifications reached the limits of the factory STI ECU, a Link G4 plug & play standalone ECU was integrated into the system. This upgrade allowed for complete control and tuning flexibility, unleashing the true potential of the engine.

Suspension and Drivetrain

To maintain the perfect balance between power and handling, a carefully chosen suspension setup was installed. The car was equipped with Tein Flex coilovers with EDFC, Cobb front and rear sway bars with upgraded mounts, Whiteline anti-lift kit, and a front Cusco 40mm top strut brace. The stock drivetrain was kept, with the exception of a Cobb Tuning short shifter and Exedy twin-disc Hyper clutch kit.


With these power-packed modifications, the STI now roared to life on the dyno, generating a maximum of 22 psi on 91 California Octane fuel, resulting in a staggering 427 whp and 397 wtq. Notably, the power graph revealed that the GT35R turbo could effectively supply the required volume of air to fill the ported and polished heads and camshaft setup.

Methanol Injection and 100 Octane Race Fuel

To push the boundaries even further, an Aquamist HFS-5 Methanol/H20 injection kit was added, and the car was run on 100 Octane race fuel. The results were impressive, with a substantial increase of 30 wtq. and whp throughout the power band. The Methanol injection system proved particularly effective during hot weather, showcasing noticeable power gains on a hot day.


After extensive trial and error, the 2006 Subaru STI now stands as a true testament to the perfect recipe for power. The combination of the FLI Stage 4 power package, custom turbo setup, standalone ECU, and well-balanced suspension has transformed the STI into a beastly machine, commanding respect on the streets and leaving a trail of impressed friends in its wake. Whether it’s for the thrill of the track or the everyday drive, this STI is the embodiment of power and drivability, ensuring its rightful place in the hall of automotive legends.

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