Stock 2015-2021 STI approx: 250whp and 260tq
300whp club
Find your EJ power plant a little underwhelming? This level of power gives you the performance to match its' rally heritage. This level of performance makes your EJ motor come alive.
Tuning Path - Street
Cobb Accessport – Tried and true, lots of extra features, and still supporting flex fuel for a lot of different packages. The Cobb Accessport gets the job done and done well. It gives you a display to monitor your state of tune, and also allows for logging if you encounter some kind of issue. Working with the factory ECU and carefully chosen components will keep excellent drivability.
A simple “Stage 1 Map” will give you some extra boost, and will allow for selecting between octane levels.
Cobb’s upgrade path makes modifying your Subaru simple. Select your package, load your tune, and enjoy your car. Custom tuning is beneficial, but not strictly necessary until you want to get the most out of your car.
Stage 1
- Includes accessport and pre-loaded maps
- Approx 260whp and 300tq
Stage 1+ Power Package
- Includes Accessport and pre-loaded maps
- Approx 270whp and 320tq
- Includes COBB SF Intake and Air Box
NEXGEN Stage 2 Package
- Includes accessport and pre-loaded maps
- Approx +25whp and 50tq over stock
- Includes COBB SF Intake and Air Box
- Includes AEM 340LPH Fuel Pump
- Includes ID1050X Injectors
- Includes COBB Fuel Rails and Lines
- Includes COBB Silicone Inlet
- Includes 1 Step Colder Plugs
Injector Dynamics ID1050X Injectors WRX-16B Bottom Adaptors 11mm (Red) Adaptors (Set of 4)
NEXGEN Stage 2 Redline Carbon Fiber Power Package
- Includes accessport and pre-loaded maps
- Approx +25whp and 50tq over stock
- Includes COBB REDLINE Carbon Fiber Intake
- Includes AEM 340LPH Fuel Pump
- Includes ID1050X Injectors
- Includes COBB Fuel Rails and Lines
- Includes COBB Silicone Inlet
- Includes 1 Step Colder Plugs
NEXGEN Stage 2 + Flex Fuel Package
- This package will get you approx +50-60whp and around +100tq over stock
- Includes everything in Stage 2 Packages plus the
- Subaru NEXGEN Flex Fuel Ethanol Sensor Kit
- Subaru Fuel Pressure Sensor Kit
- Custom tuning
- Additional performance or gains can be had with custom tuning or for different parts combinations (e.g. intake of your choice)
Limitations and caveats
- Limited DTC suppression means many modifications are not doable with the activation of a DTC.
- You cannot do TGV Deletes (immediate DTC)
- Air Pump Deletes (immediate DTC)
- Catless or aftermarket downpipes (delayed DTC)
- Any modifications that would affect emissions systems
Downpipe
- Adding an aftermarket downpipe really opens up the exhaust and turbine flow on the VF turbochargers allowing for more horsepower.
- KEEP IN MIND – even GESI catted downpipes can still get DTCs for catalyst efficiency codes and these codes can no longer be suppressed tuning with COBB Accessport.
- Make sure to follow local laws regarding any emissions devices when modifying your car.
- Full Exhaust, Intake, Silicone Inlet, Fuel System, and Flex Fuel can net you over 350whp and 400+tq with custom tuning on our dyno.
Intercooler
- Adding an upgraded intercooler is not absolutely required at this stage, but is helpful, especially when running pump fuel.
- Upgraded TMIC’s (top mount intercoolers) allow for greater cooling capacity and are simple to change and cost effective.
- Upgraded FMIC’s (front mount intercoolers) allow for greater cooling capacity, improved airflow through the core and nearly eliminates heat soak. This is one of my favourite modifications for my Subarus.
Exhaust Manifold
- An aftermarket exhaust manifold will increase flow and exhaust scavenging.
- If you want Subie rumble you need an unequal length manifold.
- RCM manifold
- For the best performance or if you prefer the smoother sound an equal length manifold is your choice.
- We really like the RCM equal length manifold
- Killer B Equal length manifold is a great performer and suits higher power levels well.
Air Oil Separator
- As power and airflow increase on EJ engines, so does the blow by. This can cause issues with oil consumption, oil pooling in the intercooler and intake manifold, carbon build up, and reduced longevity.
- Our favourite AOS to install and use is the Radium AOS. We do have a particular installation which helps ensure reliability and proper operation in colder climates.
- Great care should still be taken to ensure your AOS does not freeze unknowingly during cold weather operation.
Tuning Path - Racer
- Link Engine Management or Motec
- Choosing to upgrade your car with a standalone ECU gives you a much more flexible upgrade path.
- An endless list of features are available to suit you from 300whp to 1000whp+
- Data is king and you can get all the data you want from a standalone ECU including accelerometer data, GPS data, steering angle, brake pressure, and more.
- This can be incredibly valuable for a track car or race car.
- Safety can be worked in the tune in new ways, including oil pressure based rev-limiters, internal logging up to 1000hz, lambda/afr protection strategies, and more.
- The tuning path for a standalone ECU managed EJ Subaru to 300whp is similar but more breathing modifications can be taken advantage of. Keep in mind local laws when modifying your vehicle.“Stage 1” - approx 265whp and 310tq
- Standalone ECU and Tune – approx 265whp and 310tq
- Fast acting IAT sensor and install.
- FBO – Up to 300whp and 360tq
- Everything included in “Stage 1” plus:
- Intake of choice
- Full exhaust of choice including downpipe (can be catless) and catback
- Silicone Inlet
- TGV Deletes
- Intercooler (TMIC or FMIC)
- FBO + Injectors and Fuel System - approx 320whp 360+tq
- Everything included in “Stage 1” and “FBO” plus:
- ID1050X (Max 400whp E85) or ID1300X (Max 500whp E85)
- Fuel rails and regulator of choice (Radium recommended)
- RCM 340lph pump
- FBO + Flex – approx 360+whp and 400+tq
- Everything in FBO + Injectors and Fuel System plus:
- AFR ethanol sensor kit
- Requires E85 and Pump Tuning (Tunes x2)
- Intercooler
- Adding an upgraded intercooler is not absolutely required at this stage, but is helpful, especially when running pump fuel.
- Upgraded TMIC’s (top mount intercoolers) allow for greater cooling capacity and are simple to change and cost effective.
- Upgraded FMIC’s (front mount intercoolers) allow for greater cooling capacity, improved airflow through the core and nearly eliminates heat soak. This is one of my favourite modifications for my Subarus.
- Exhaust Manifold
- An aftermarket exhaust manifold will increase flow and exhaust scavenging.
- If you want Subie rumble you need an unequal length manifold.
- RCM manifold
- For the best performance or if you prefer the smoother sound an equal length manifold is your choice.
- We really like the RCM equal length manifold
- Killer B Equal length manifold is a great performer and suits higher power levels well.
- Air Oil Separator
- As power and airflow increase on EJ engines, so does the blow by. This can cause issues with oil consumption, oil pooling in the intercooler and intake manifold, carbon build up, and reduced longevity.
- Our favourite AOS to install and use is the Radium AOS. We do have a particular installation which helps ensure reliability and proper operation in colder climates.
- Great care should still be taken to ensure your AOS does not freeze unknowingly during cold weather operation.
400-500whp Club
Looking to surprise some quick cars and punch well above your weight class? A 400whp Subaru is a lot of fun, both on the street or the track.
An upgraded turbo is needed to get to this power range and should be carefully selected based on your goals.
If you want to reach this power on pump fuel the parts selection will be different than if you want to make the power on flex fuel.
If you have plans of going in to the engine, Kelford camshafts and springs are a great idea at this power level, and really help the power band and peak power. The Kelford 264 camshafts work expetionally well with any of these turbo options. Camshafts will make a bigger turbo feel like a smaller turbo but pull even harder up top.
If you are still on stock clutch, now is a great time to upgrade. Our recommended clutch for anyone shooting over 400whp is the Exedy Ceramic Twin-Plate clutch. ETS TMIC or FMIC are required for this power level.
- Tuning Path – Street – approx 390+whp and 340tq on pump fuel
- Everything in NEXGEN Stage 2, Plus:
- FMIC
- 93 Octane Shell Fuel
- Downpipe
- Turbo Upgrade
- Tomioka 3076 or equivalent
- 21-24psi boost typically depending on car and other mods.
- Radium AOS
- Tuning Path – Street – Flex Fuel – approx 400whp and 360+tq on E85
- Everything in NEXGEN Stage 2 + Flex, Plus:
- TMIC or FMIC
- Turbo Upgrade
- Tomioka 3076 or equivalent
- Radium AOS
- Notes:
- You will run out of fuel around 400whp on E85 with ID1050X (about 90% duty cycle depending on base pressure).
- Very safe 400whp, meaning low boost and you can stay away from the “knock threshold”
- If you are keeping the stock downpipe, flex fuel really helps reach this power level.
Tuning Path – Racer – Pump Fuel - approx 400-440whp and 370+tq
- Everything in “FBO + Injectors and Fuel System”, plus:
- 93 Shell
- TMIC or FMIC
- Tomioka 3076, Precision 58mm Gen 2 (3” inlet), TPC G30-900 Twin Scroll (3” Inlet)
- Radium AOS
- With Kelford 264 cams, this setup will make 420whp+ on Shell 93 with quicker spool.
Tuning Path – Racer – Flex Fuel – up to 500-560whp and up to 500+tq
- Everything in “FBO + Injectors and Fuel System”, plus:
We recommend an Outfront Motorsports closed deck short block with ½” head studs to take full advantage of these turbos on E85
- E85
- TMIC or FMIC
- Radium AOS
- ID1700X Injectors
- Radium in tank dual pump hanger with twin pumps (ECU controlled secondary)
- Tomioka 3076, Precision 58mm Gen 2 (3” inlet), TPC G30-900 Twin Scroll (3” Inlet), RCM/PTE 58mm Gen 2 (Twin Scroll)
- 3” Inlet turbos like the Precision Gen 2 58mm (Open Scroll), TPC G30-900 (Twin Scroll), or RCM/PTE Gen 2 58mm (Twin Scroll) really shine on the top end.
- A Killer B – Holy header or ETS V2 Max Flow (If plans for higher power)
- Killer B Super G – Oil Pan
- Kelford 264 camshafts for best response or Kelford 272 camshafts for best top end power.
- We have made around and over 550whp many times with similar combos, torque is typically limited based on shortblock and head sealing used.
- Notes:
- At this power level, every choice you have made with your build starts to make bigger differences. Exhaust manifold, down-pipe (is it catted/catless), catback (full 3” with no restrictive sections), wastegate spring selection for turbo (external vs internal and selected spring pressure), turbo inlet pipe, intercooler (ETS 4” FMIC recommended).
- Engine should be built to optimize your setup or future plans. We like to keep torque around 450wtq max on semi-closed deck blocks. Closed deck blocks begin to be limited be head sealing. 11mm ARP 2000 studs with MLS can be pushed, but we recommend staying around 450wtq for head gasket integrity. ½” studs we like to keep to 550wtq range on an RCM head gasket. If wanting north of 550wtq we recommend a cut-ring gasket to improve head sealing.
600whp+
This is getting in to serious power production.
- Tuning path – Racer – Flex fuel
- Everything in “Tuning Path – Racer – Flex Fuel – up to 500-560whp and up to 500tq” Plus:
- Rotated turbo setup, picked based on your particular power goals. Precision 6266 or bigger is our pick when shooting for north of 600whp.
- Extreme Turbo Systems is our go to for rotated turbo setups on LHD Subarus
- RHD Subarus we recommend the kits from Roger Clark Motorsports
- Kelford 272 or 280 camshafts and springs – power goal dependant.
- AFR Autoworks CNC Ported Cylinder Head Package and +1mm Ferrea valves.
- Closed Deck Block.
- Notes:
- At this power level, every choice you have made with your build starts to make big differences. Exhaust manifold, down-pipe (is it catted/catless), catback (full 3” with no restrictive sections), wastegate spring selection for turbo (external vs internal and selected spring pressure), turbo inlet pipe, intercooler (ETS 4” FMIC recommended).
- Engine should be built to optimize your setup or future plans. Closed deck blocks begin to be limited by head sealing.
- 11mm ARP 2000 studs with MLS can be pushed, but we recommend staying around 450wtq for head gasket integrity.
- ½” studs we like to keep to 550wtq range on an RCM head gasket. If wanting north of 550wtq we recommend a cut-ring gasket to improve head sealing.
- Up to 800whp – ½” ARP 2000 Studs with Cut Ring Gaskets
- 800whp+ ½” ARP 625 Studs with Cut Ring Gaskets