Best Modifications STI Ej25

The Subaru STI is one of the most popular “tuner cars” sold over the past 20 years. Featuring a turbo EJ25 engine the STI make great power from the factory and with a few basic mods evolve into a truly fun and fast car to drive in just about any condition. 

Below is a list of modifications that are proven to make reliable power on any STI. We have been using all or combinations of these parts regularly on hundreds of STI builds around the world with great success each and every time. 

STI Exhaust 

Cat-back exhaust, downpipe and headers are 3 of the best ways to help your EJ25 breath. The factory exhaust and cast manifolds are very restrictive to the exhaust flow. Upgrading to a Turbo back exhaust and headers will net 15-20% increase in power simply by allowing the engine to exhale do to the lower exhaust back pressure. Headers also make the EJ25 sound amazing! 

STI Fuel System & Turbo Upgrades

As you make more power with the STI the stock fuel system starts to reach its limits. Using ID1050x injectors and AEM 340lph fuel pump that come in the Cobb Fuel System package listed below flow enough to support over 500HP.

While the OEM STI turbo is a great little turbo that spools fast it lacks airflow up top and power falls off hard in the high RPM ranges. Using a Cobb 3 port boost solenoid will help to get the most accurate boost control out of any turbo but if you want more power than the stock STI turbo can support we have the FP green stock location upgrade for a simple bolt on upgrade. We also offer full rotated turbo kit from ETS and Perrin for those STI builds looking for 600+ WHP.