Specially developed for use on racetracks where lower noise levels are required Optional headers available for some models to improve torque and power, especially from the mid-range upwards PART #1811-4052 must be combined with either PART #1812-0325 link pipe for mounting on stock headers or PART #1812-0324 link pipe for mounting on the header set from the PART #1810-2344 Evolution Line kit. Evolution line PART #1810-2344 or Racing Line PART #1810-2758 (the collector and headers with associated fitting material (flanges, springs, inner sleeves and lambda plugs - please refer to schematics of the mentioned systems)). Fitting kit PART #1861-1254, including the muffler bracket and clamp, must be ordered and purchased separately to install PART #1811-4052.. MUFFLER TRACK DAY R1