BMW X3M F97 & X4M F98 S58 JB4 Tuning Box

The JB4 for S58-powered X3M F97 and X4M F98 is a plug-and-play piggyback tuner that delivers real-world gains: up to 150whp on E85, or 80whp on UK 99 RON. No ECU flashing, no coding, no cutting.

• Eight S58-specific maps including ethanol, competition and launch-optimised
• JB4PRO app for iOS/Android: switch maps, log 20+ parameters, update firmware
• Fully reversible - retains OEM drivability, safety systems and factory diagnostics
• 5-year warranty; assembled and S58-tested in the USA for UK-spec engines

Optional JB4PRO board adds Bluetooth, onboard logging and flex fuel support via plug-and-play harnesses.