For the Milwaukee Eight motor, Cobra modified their PowerPort by enlarging it to become a pulse chamber that accelerates exhaust scavenging to produce the kind of power riders expect, The round shape, bulging from between the heat shields gives a clue to the real power potential it offers, Includes 18mm bungs up near the heads, allowing the use of wideband oxygen sensors; Perfect for use with the new Harley-Davidson auto tuner, Stock H-D mufflers will not work with this head pipe because of the stock muffler*s internal construction. Most aftermarket mufflers will fit