I understand how a header would work by using the vacuum behind the first pulse to help pull out the second pulse. That's why primary length and diameter are so important. There is probably some forumala to figure out the ideal length for a given engine speed and size. Would splitting the exhaust 3 in front and 3 in back make the 2 primary pipes act like headers and the Y pipe a collector? Would this make more power or torque than just dual exhaust comming from a split manifold ? After all even the factory got into the act with the 79 to 84 truck engines. They probably went 2 into 1 because at the time the idea of 2 cats was unheard of. Jay6155
