Improves Horsepower and offers a louder sound  - These are Direct replacement Brentech performance H & X pipes - They are a direct bolt on to factory or aftermarket headers. They also has factory O2 sensor locations making the swap easy:  Please remember these are for Off Road Race use and are not for highway use due to the fact that they do not have any catalytic converters. H pipes are more suited to Flowmaster mufflers or a chambered muffler - X pipes are recommended for higher revving 4.6 applications and where a straight thru mffler is used like Magnaflow or Borla.