The engine code for the Subaru WRX STI’s 2.5-liter turbocharged flat-four is EJ257.
The EJ257 belongs to Subaru’s EJ family of horizontally opposed four-cylinder engines. Its 2,457-cubic-centimeter displacement comes from a 99.5-millimeter bore and 79.0-millimeter stroke. In WRX STI applications, it was paired with turbocharging and Subaru’s symmetrical all-wheel-drive performance platform, giving the model its distinctive boxer-engine character and strong tuning following.
The code is easy to confuse with EJ20 and FA20. EJ20 generally identifies a 2.0-liter branch of the EJ family, while FA20 is a newer 2.0-liter Subaru boxer design used in later turbocharged WRX models. The regular 2.5-liter WRX in several markets commonly used the related EJ255 rather than the STI’s EJ257.
Engine codes can vary by market, model year, emissions equipment, and internal specification, so “EJ257” is the canonical answer for the familiar 2.5-liter WRX STI engine. It identifies the engine family and variant, not the turbocharger, transmission, or a complete vehicle trim level.