2015-2021 Subaru STI Engine Parts

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    The Power of the Subaru STI’s EJ257 Engine

    The 2015-2018 STI produced 305 horsepower and 290 lb-ft of torque. Subaru's limited-edition 2018 STI Type RA was the first to get an updated EJ257, and the change carried into the regular STI for 2019: a new air intake, a high-flow exhaust, a retuned ECU, and stronger pistons pushed output to 310 horsepower, while torque held at 290 lb-ft.

    The block underneath is a semi-closed deck aluminum design, stronger than the fully open deck used in some other Subaru turbo engines, though every EJ257 shares the same core architecture regardless of year. That consistency is why a Subaru STI engine from a 2016 car and a 2020 car can share most of the same parts, aside from year-specific electronics and boost hardware.

    Where the Stock Block Tops Out

    Every 2015-2021 STI ships from the factory with the same Subaru STI turbo, the IHI VF48 (OEM part number 14411AA700). It's a proven unit that supports roughly 350 wheel horsepower with supporting fuel and tuning, which covers most street builds without a turbo swap. 

    Push past that and the limiting factor becomes the block, not the turbo. The EJ257's semi-closed deck handles factory boost without issue, and most builders keep the stock STI short block reliable into the 400 hp range with the right supporting mods. Past that, a built short block with forged internals becomes the safer foundation, especially if you're planning to run higher cylinder pressure for an extended period.

    JDMuscle stocks turbos, short blocks, and every EJ257 support part your Subaru STI engine build needs, backed by same-day shipping and a price match guarantee.

    FAQs

    What engine does the 2015-2021 STI use?

    Every 2015-2021 STI runs the EJ257, a 2.5-liter turbocharged boxer-four. Subaru kept this engine through the STI's final model year in 2021, while the WRX switched to the smaller FA20 in 2015.

    How much horsepower does a stock STI make?

    The 2015-2018 STI makes 305 horsepower and 290 lb-ft of torque. Subaru raised that to 310 horsepower starting with the 2019 model year, matching the output the limited-edition 2018 Type RA introduced first.

    What Subaru STI turbo comes stock on 2015-2021 models?

    The IHI VF48 is the stock turbo across every Subaru STI engine built between 2015 and 2021. It supports around 350 wheel horsepower with supporting mods before a turbo upgrade makes sense.

    When should I upgrade to a built engine block?

    The factory semi-closed deck block reliably handles builds into the 400 hp range. Past that, or if you're running sustained high boost, a built block with forged internals protects against the failures that show up at the factory block's ceiling.