Unitronic Unlocks the 2025 Audi RS3, With a Stage 2 E85 Tune Claiming 638 HP

The five-cylinder RS3 has always responded to a tune, but the facelifted car's newer ECU kept tuners waiting. Unitronic is now in. PASMAG reported on August 17 that Unitronic released ECU performance software for the 2025-and-newer Audi RS3 in North America, with its 2.5 TFSI EVO (DXH) engine and Bosch MG1CS164 ECU.

There are three tiers: Stage 1, Stage 1+ and Stage 2. The top number is the one getting attention. On E85, Stage 2 is rated at up to 638 hp and 534 lb-ft, which PASMAG says works out to gains of up to 201 hp and 152 lb-ft over stock.

Flex fuel without reflashing

The E85 numbers depend on UniFLEX, Unitronic's flex-fuel system. It adjusts automatically for ethanol content anywhere from gasoline to E85, so you do not need to reflash when you switch fuels. Ethanol content and fuel temperature show up in the UniE85 Manager app and in the RS3's Virtual Cockpit. An optional Advanced Features package adds app-adjustable standing and rolling launch control, exhaust overrun settings, exhaust flap control, an immobilizer function and valet mode.

The catch

Installing the software starts with unlocking the Bosch ECU, and right now Unitronic does that only at its headquarters. Owners ship the ECU in, and Unitronic says unlocks are typically completed the same day they arrive. After that, updates happen at home over the OBD-II port with UniCONNECT+. The important fine print: once the ECU is unlocked, it cannot be reflashed back to the stock calibration without overwriting the unlock, according to PASMAG's report. Think about warranty and resale before you send it out.

Support for other markets is planned. Pricing was not included in the report. For RS3 owners, the math is simple: the five-cylinder already sounds like nothing else in the class, and a tune that adds up to 201 horsepower on E85 turns a fast car into a genuinely silly one. Just make sure the fuel, the clutch packs in the transmission and the tires are up to the job before you plug into Stage 2.