Cooper S Convertible
B48 / B46 (US)

Stage 1 on the F57 Cooper S Convertible moves the B48 / B46 (US) from 189–192 bhp · 280 Nm at the factory to 245–260 bhp · 360–400 Nm — no hardware required. The map goes in over OBD on BM3, MHD or MG Flasher in around 15 minutes. Torque spreads significantly through the mid-range, and throttle response is noticeably sharper from the standard hardware.

This page covers the F57 — the Convertible body only. The F57 shares the B48 / B46 (US) 2.0-litre turbo with the F54 Clubman, F55 5-door, F56 3-door, and F60 Countryman; all run the same core calibration and the same stage targets. Every map Samuel delivers is built to the specific car — fuel grade, hardware, VIN — not pulled from a shared base file.

Stage 2 on the F57 targets 270–285 bhp · 420–460 Nm and requires an intercooler, decat or sports cat, and intake — cooler plugs are also advised. The standard turbo and fuel system hold within Stage 2 figures on the B48 / B46 (US); no fuel pump upgrade is needed at this stage.

On the right hardware, the B48 / B46 (US) in the F57 reaches around 400 bhp. Stage 1 and Stage 2 both run the stock turbo. Beyond Stage 2, a hybrid or full big-turbo conversion is required alongside supporting fuelling — the calibration at that point is bespoke to the specific build spec. One reliability note for the Cooper S: the standard B48 runs a weaker piston than the JCW spec, so forged internals come before high Stage 3 power figures are safe long-term.

The F57 Convertible runs the Aisin/ZF automatic, which responds well to xHP calibration as torque increases. At Stage 2 — where torque reaches 420–460 Nm — xHP is strongly recommended to handle the extra load cleanly through the gearbox. At Stage 1 it's optional, but most owners notice a clear difference in shift character. Manual-gearbox variants don't need it.