Create your own Anti-Reverse system with our Torke Valves. They fit into the exhaust at header to cylinder head connection. It gives the correct back pressure within the system by creating a venturi. At low engine speeds the taper of the torke valve increases back pressure resulting in increased low RPM power and torque. At high engine speeds, the venturi increases exhaust gas velocity. This maximizes engine power by increasing the rate at which the exhaust gases are drawn from the exhaust ports. Fits all OEM and aftermarket pipes on all Evolution Sportsters, Evolution Big Twin and Twin Cams. Sold in sets of two.