The factory turbocharger on the updated B48 engine pushes serious air to achieve 201bhp in the Cooper S and 231bhp in the JCW. However, as you increase boost pressures with tuning boxes or future ECU calibrations, boost holding becomes critical. Swap out the factory diverter for an uprated Diverter Valves (dump valves) unit to ensure your engine holds maximum pressure securely without leaking during rapid acceleration, keeping your forced induction system operating flawlessly.