pneumatically controlled, based on manifold pressure. Just like a throttlebody but in the exhaust pipe. I thought of this idea after noting the dramatic decrease in bottom end torque on Dee's car after he punched out the cats - and I mean it was night and day. It will also quiet down the tone of the exhaust at idle and cruising, as well as improve gas mileage during cruise (since there wont be as much fuel blow-through during valve overlap). I am planning to use a pair of wastagete actuators to control the butterfly valves, with an adjustable base setting to set the minimum closing as well as a full-open stop. We shall see if it works...
