Subaru Performance Modification Guide

For enthusiasts looking to enhance the performance of their Subaru, following a structured modification path ensures optimal gains, reliability, and drivability. This guide outlines typical upgrade paths for different generations of WRX and STI models, covering intake, exhaust, fueling, and when to prepare for engine builds.

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2002 WRX (GD Chassis)

Stage 1: Intake & Tuning

• High-flow panel filter or cold air intake (properly tuned)

• ECU tune (Cobb Accessport, Open Source tuning)

Stage 2: Exhaust & Supporting Mods

• Turbo-back exhaust (bellmouth downpipe for best gains)

• Upgraded intercooler (top-mount or front-mount for higher boost levels)

• High-flow fuel pump (Walbro 255lph or better)

• 3-port boost control solenoid for improved boost control

• Pro tune to optimize power and reliability

Stage 3: Fuel System & Turbo Upgrades

• Upgraded injectors (1000cc always recommended at first - save time later - 650cc+ for moderate boost, 1000cc+ for E85) - must have fuel pressure regulator, lines and rails to ensure proper fueling with minimal compensations.

• 16G, 18G, 20G, or larger turbo upgrade. Depends on your overall power goal and use for the car. Larger turbos will take longer to spool so a 68 trim turbo for example wouldn't be recommend for Autocross.

• External wastegate setup (optional but recommended for boost control)

• Pro tune required

Engine Build Prep

• When exceeding 350whp, consider forged pistons and rods

• ARP head studs for high boost levels

• Upgraded clutch and transmission reinforcement recommended

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2014 WRX & WRX STI (GR/GV Chassis)

Stage 1: Intake & Tuning

• Cobb Accessport or Opensource Tuning

• High-flow panel filter or cold air intake (must be tuned for MAF scaling)

Stage 2: Exhaust & Supporting Mods

• Turbo-back exhaust

• Upgraded fuel pump (DW65C, Walbro 255lph+)

• Upgraded top-mount intercooler (larger core for better cooling)

• Pro tune required

Stage 3: Fueling & Turbo Upgrade

• Larger injectors (ID1050X for pump gas, 1300cc+ for E85) - must have fuel pressure regulator, lines and rails to ensure proper fueling with minimal compensations. The fueling components should be done minimum stage 3 levels, but stage 2 very highly recommended.

• Blouch, Boostlabs, BCP Stock location turbos are great - many other brands with great capability are out there.

• E85 conversion with flex-fuel kit for increased power and knock resistance

• External wastegate (optional but beneficial)

Engine Build Prep

• Built short block recommended when surpassing 350-400whp

• Upgraded valve springs and cams for high-RPM applications

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2015 WRX (FA20DIT Engine)

Stage 1: Intake & Tuning

• Tuning is mandatory for any modification

• High-flow panel filter or intake (must match tuner specifications)

Stage 2: Exhaust & Intercooling

• J-pipe (downpipe replacement)

• Cat-back exhaust for sound enhancement

• Larger top-mount intercooler for lower intake temps - Verticooler is best for top mounted setups but front mounted intercoolers are the best overall especially in warmer climates.

• EBCS (electronic boost control solenoid) for better boost response and control

• Pro tune required

Stage 3: Fueling & Turbo Upgrade

• In tank fuel pump such as DW300C or AEM340 is required for up to E60. Upgraded HPFP (high-pressure fuel pump) by Nostrum is required for E85. E50/E60 will provide the best power possibility with the least amount of stress on the fuel system.

• Flex-fuel tuning for substantial power gains

• Turbo upgrade - Boostlabs, Tomioka, Steamspeed, Socal Upgrades have proven great stock location with big power capabiltiies.

Engine Build Prep

• FA20DIT engines suffer from weak connecting rods above 400whp

• Consider closed-deck block reinforcement and forged internals when pushing past this limit

• Port injection and larger turbo becomes an option for desired power levels exceeding 450-500whp. This can be done on Cobb Accessport or standalone ecu like Motec M1.

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2015+ STI (VA Chassis, EJ257 Engine)

Stage 1: Intake & Tuning

• Cobb Accessport or Opensource Tuning

• High-flow panel filter or intake (requires tuning)

Stage 2: Exhaust & Fueling

• Turbo-back exhaust (catless or high-flow)

• Upgraded fuel pump (DW300C or Walbro 450 for E85 setups)

• Injector upgrade (ID1050X for 450whp MAX on E85, 1300cc+ for higher boost on E85 - typically 550-600whp on base fuel pressure will be the limit on e85)- must have fuel pressure regulator, lines and rails to ensure proper fueling with minimal compensations.

• Front-mount intercooler for better heat management

• Pro tune required

Stage 3: Turbo & Built Engine Prep

• Turbo upgrade (Blouch Dom 1.5XTR, FP Green, or rotated turbo setup)

• E85 conversion for higher power and safety 

• External wastegate setup for precise boost control

Engine Build Prep

• Consider forged pistons and rods past 400whp

• Closed-deck conversion for extreme boost applications

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2022+ WRX (FA24DIT Engine)

Stage 1: Intake & Tuning

• ECU tune is essential for any performance modification

• High-flow panel filter or cold air intake (tuned accordingly)

• Cat-back exhaust for sound and slight flow improvements

Stage 2: Exhaust & Cooling

• J-pipe replacement (downpipe alternative)

• Intermediate Pipe

• TMIC or FMIC (highly recommended)

Stage 3: Fueling & Turbo Upgrades​

• Turbo upgrade ( BCP VB500 or other stock location turbos)

• Flex-fuel conversion for optimized power and knock resistance - In tank pump setup recommended due to fueling demand with higher boost levels.

Engine Build Prep

• Stock internals are stronger than FA20DIT, but rods and pistons should be upgraded past ~400-450whp to promote longevity.

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Conclusion

Following a structured modification path helps ensure reliability and maximizes gains at every stage. Whether you're aiming for a daily driver with improved response or a fully built track machine, understanding the best upgrade order prevents costly mistakes. For expert tuning, installation, and custom builds, contact us today!