STI tuning tips for reliable power
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.
If you have a 2015+ WRX be sure to check out our WRX specific article: Best WRX Modifications.
STI Cold Air Intake
The first mod for any EJ25 powered STI should always be an intake. At minimum a high flow drop in air filter used with the oem air box.
For those that want a bit more performance the Cobb Intakes are a perfect choice. Starting with the Cobb SF intake this budget friendly cold air intake set the industry standard for the Subaru market.
Those that want the best of the best should use the STI Cobb Redline Carbon Fiber Intake. The Cobb Redline intakes are hands down the best performing intakes on the market. Made from Carbon Fiber these intakes not only flow great they also look amazing in your engine bay and don’t heat soak like an aluminum, Titanium or steel intake tube does.
- STI Cobb SF Intake 2015+ Subaru STI
- STI Cobb Redline Carbon Fiber Intake 2015+ Subaru STI
- 08-14 STI/WRX SF Intake
- 02-07 STI/WRX SF Intake
Cat-back exhaust, downpipe and headers are 3 of the best ways to help your EJ25 breathe. 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!
- Perrin Headers STI All years
- Killer Bee headers STI All years
- Cobb Titanium exhaust STI/WRX 02-07
- Cobb Catback exhaust Quad tip 08-14 sti
- Cobb Bellmouth Downpipe w/highflow cat STI 08-21 STI
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.
Those looking for Injectors and fuel system parts to support over 500HP can check out our blog here for a complete Guide to The Best STI and WRX Fuel Injectors.
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.
- Cobb fuel system package STI 08-2021 STI
- ID1050x STI All years using top feed fuel rails
- AEM 340lph fuel pump STI All years
- Cobb 3 port boost solenoid 2015-2021 STI
- FP Green Turbo STI All years
- ETS STI Twin Scroll Turbo Kit This is hands down the best turbo kit on market, if you are looking for the best of the best this turbo kit is for you.
Rotated Mount Turbo Kits & Engine Packages
Those looking to push power past the 500WHP mark will want to use our IAG engine packages combined with our ETS Rotated Vband turbo kit, ID equipped fuel system and either our Motec, Haltech, Emtron or Link ECU standalone engine management systems.
We offer turn key packages for 400-1200HP on the EJ25 platform. If you want to build your subi right the first time around we are here to make it happen smooth and simple with the best pricing and services in the industry.
If you have any questions or request for your STI project don’t hesitate to contact us. We are here to support you and your build with all the parts, tech advice and tuning you need to get your STI running exactly the way you want.
For those building a 2015+ WRX with the FA20dit engine check out our WRX specific post here: WRX Best Mods FA20 in this article we breakdown all the basic bolt on modifications in detail to help ensure you choose the best possible parts to reach your power goals while matching your driving style.
Product on salePerrin Air Oil Separator Subaru WRX & STI$420.00
Product on saleETS Front Mount Intercooler and Piping Kit 08-14 Subaru WRX STI$1,544.00
Perrin Equal Length Headers 2004-2021 STi, 02-14 WRX$1,274.15
Link ECU STI & WRX 2007-2021 Plug in WRXLink V11$1,699.00
Product on saleMotec M150 2008+ STI Package$4,725.00
Clutch Masters 850 Series Street Twin Disk WRX STI 2004 – 2021$2,250.00