HKS has released Phase 2 of its Mastery ECU reflash for the Subaru WRX S4 and Levorg, priced at ¥154,000 including tax. HKS lists output of up to 294 PS on the Levorg, with the WRX S4 gaining 52 Nm of torque and the Levorg 47 Nm.
The August 26 release covers the FA24 turbocharged cars — Japanese-market VBH-chassis WRX S4 and VNH Levorg models listed from November 2021 onward.
HKS Mastery ECU Phase 2 output and torque figures
All figures below are HKS-claimed values, as carried by Response's coverage — not independently measured.
| WRX S4 (VBH) | Levorg (VNH) | |
|---|---|---|
| Power | 267 → 278 PS (196 → 204 kW) | 277 → 294 PS (204 → 216 kW) |
| Torque | 377 → 429 Nm (38.4 → 43.7 kgf-m) | 376 → 423 Nm (38.3 → 43.1 kgf-m) |
| Boost | 103 → 135 kPa | 108 → 132 kPa |
| Price | ¥154,000 incl. tax | ¥154,000 incl. tax |
Beyond the peaks, Phase 2 revises the fuel, ignition and torque maps with a focus on mid-range torque, and raises the speed limiter from 180 km/h to 240 km/h. The original 180 km/h limit is electronically imposed, as is common on Japanese-market vehicles.
One hard restriction: HKS says the reflash must not be used together with its own Power Editor or Power Editor R piggyback controllers, citing the risk of conflicting control strategies causing engine trouble. This is an either/or product.
What this means for US-market WRX owners
The FA24 turbo four in these cars is from the same engine family fitted to the US-market WRX, which makes Japanese ECU development for it worth watching from abroad. That said, this is a Japanese-market product listed for the VBH and VNH chassis codes. US-market compatibility has not been announced, and differences in calibration and vehicle specification mean these figures should not be assumed to apply to a US-spec WRX.
The wider context is simple enough: with no current WRX STI in Subaru's Japanese lineup, aftermarket ECU calibrations like this remain one of the few routes to meaningfully more performance from the CVT-only WRX S4.