Milltek GPF/OPF bypass system designed for vehicles with flange connection to OE downpipes. This system features 3.15-inch (80mm) pipework and requires a Stage 2 ECU remap or an OPF/GPF Bypass Module for optimal performance.3.15-inch / 80mm pipe diameterFits to OE Downpipes and OE OPF/GPF back syste..