HKS 70020-AF108 Racing Suction Intake System for 2015-2021 Subaru WRX STI EJ25

Vehicle Fitment

• 2015-2021 Subaru WRX STI Sedan (VAF platform - EJ257 2.5L turbocharged flat-4, AWD - all trims)
• 2015-2018 Subaru WRX STI Hatchback (VAB platform - EJ257 2.5L turbocharged flat-4, AWD - all trims)

Fitment Notes

• Fits all EJ257-equipped VAB/VAF WRX STI variants - fitment does not vary by trim level for this intake system
• Does NOT fit the Subaru WRX (non-STI) VA body - the WRX uses the FA20DIT engine and a different intake layout
• With the air duct (air guide) installed: compatible with stock ECU tune on a standard vehicle or a vehicle with only a cat-back exhaust - no ECU recalibration required in this configuration
• With the air duct removed: ECU tune is required - removing the air guide increases airflow beyond the stock MAF calibration range and will cause fueling and boost issues without a recalibration
• When combined with a metal catalyzer (high-flow cat or catless downpipe): ECU setting is also required, regardless of air duct configuration
• This product is not CARB legal and is not for sale in California
• For the bundled kit including the 70029-AF005 airflow adapter guide, see HKS 70026-AF004; the 70029-AF005 adapter requires the 70020-AF108 as its base installation

Features

• Racing Suction system design - combines a Super Power Flow (SPF) open-element filter with a vehicle-specific aluminum suction pipe to address both stages of intake restriction on the VAB/VAF STI: the OEM airbox and the corrugated rubber hose between the airbox and the turbo inlet. The OEM corrugated hose creates internal turbulence as induction air strikes the ridges of the corrugation; the smooth-bore aluminum pipe eliminates this entirely, resulting in a measurable airflow improvement verified on HKS's flow bench
• Vehicle-specific aluminum suction pipe - the pipe angle, length, and bend radius are engineered specifically for the VAB/VAF engine bay geometry to maximize induction efficiency and airflow velocity at the turbo inlet. Polished / brushed aluminum finish improves the engine bay's appearance compared to the OEM rubber assembly
• Super Power Flow filter with Hyper Stealth Frame - the updated Reloaded-generation SPF filter features the Hyper Stealth Frame, which provides 27% more filter intake surface area than the previous Super Stealth Frame generation. Greater surface area increases the volume of air the filter can process simultaneously, reducing restriction at the filter face under high-load conditions
• Black anodized aluminum backplate with white HKS logo - the alumite-processed backplate provides superior rigidity and durability compared to a plastic backplate; the outer edge of the funnel is secured firmly to the backplate to prevent separation or deformation under sustained high-flow conditions
• Removable air duct (air guide) with wide-opening design - the newly designed air duct is a unique feature of this kit that allows it to be run on a stock ECU without recalibration when installed. The duct guides cooler ambient air toward the filter while moderating the total airflow increase to remain within the stock MAF's calibrated range. Removing the duct maximizes airflow performance but requires ECU tuning to take full advantage and avoid fueling issues
• HKS flow bench validated - the complete system has been tested on HKS's flow bench against the stock intake system, confirming a significant reduction in intake restriction across the airflow range
• Distinctive induction sound - the aluminum pipe and open-element SPF filter produce a characteristically sporty induction tone that amplifies the EJ257's turbo spool and mid-range character
• Engineered and manufactured in Japan by HKS

Specifications

• Part Number: 70020-AF108
• Series: Racing Suction
• Application: Subaru WRX STI VAB/VAF - EJ257 2.5L turbocharged flat-4
• Pipe Material: Aluminum (polished / brushed)
• Filter Type: Super Power Flow (SPF) - Hyper Stealth Frame, red element
• Backplate: Black anodized aluminum with white HKS logo print
• Air Duct: Included, removable
• ECU Tune Required (stock, air duct on): No
• ECU Tune Required (air duct removed or metal cat): Yes
• CARB Legal: No - not for sale in California
• UPC: 4957266275559
• Country of Manufacture: Japan

Included Components

• 1x vehicle-specific aluminum suction pipe
• 1x Super Power Flow filter assembly (Hyper Stealth Frame, red element, black anodized aluminum backplate)
• 1x removable air duct (air guide)
• Silicone couplers, worm clamps, brackets, and mounting hardware

Product Description

The HKS 70020-AF108 Racing Suction is a complete intake system for the 2015-2021 Subaru WRX STI (VAB/VAF) built around the EJ257 2.5L turbocharged flat-4. Racing Suction is HKS's highest-tier vehicle-specific intake line, combining a Super Power Flow open-element filter with an application-engineered aluminum suction pipe - addressing both the restrictive OEM airbox and the corrugated rubber hose that connects it to the turbo inlet. The corrugated OEM hose is a significant source of intake turbulence: as induction air travels over the internal ridges of the corrugation, it creates swirl and flow resistance that robs the turbocharger of the clean, high-velocity airflow it needs for efficient spool. The smooth-bore aluminum pipe eliminates this turbulence entirely, and HKS has validated the system's performance improvement at their in-house flow bench against the stock intake assembly.

The Super Power Flow filter uses the Hyper Stealth Frame from the Reloaded generation, which provides 27% more filter face surface area than the previous Super Stealth Frame - increasing the total volume of air the filter can process without raising restriction. The filter assembly is anchored to a black anodized aluminum backplate with the outer funnel edge firmly secured to the plate, providing the structural rigidity necessary to prevent separation or deformation under sustained high-flow operation. The alumite surface process on the funnel adds durability and contributes to the kit's distinctively purposeful JDM engine bay aesthetic alongside the polished or brushed aluminum suction pipe.

A key feature unique to this kit is the removable air duct (air guide). When installed, the air duct allows the system to operate within the stock MAF's calibrated airflow range, making the Racing Suction compatible with a stock ECU on a standard vehicle or one equipped with only a cat-back exhaust - no ECU recalibration is required in this configuration. Removing the air duct removes the flow limitation and delivers maximum intake performance, but does require ECU tuning to properly account for the increased airflow and extract the full power gain. ECU recalibration is also required when the system is paired with a metal catalyzer or high-flow downpipe. For owners looking to add an airflow adapter guide, the 70029-AF005 is a compatible add-on that requires this kit as its base; both the Racing Suction kit and the adapter guide are also available as a single bundle under HKS 70026-AF004.