Normally, replacing a stock air cleaner with a Hypercharger will net you a 7-9 horsepower increase at the rear wheel, with no other modifications. Add a carb recalibration kit, a good performance exhaust system (not drag pipes) and a 12-14 horsepower increase is normal.
There is no need to purchase any additional components for this application
1991-06 XL with stock carb - For use with H-D breather 1 (late inlet)
H-D Breather for XL Refers to Harley-Davidson P/N 29281-91T
NOTE: Each application lists “early inlet”, “late inlet”, or “Marelli Inlet” in parenthesis. An early inlet air cleaner will bolt directly to a Keihin Butterfly, Bendix, or Zenith carburetor. A late inlet air cleaner will bolt directly to Harley’s 40mm or 44mm Keihin CV carburetor as well as the Delphi E.F.I. system found on 2001 Softails and all 2002-08 Twin Cams with E.F.I. (ex. 2008 Touring). A Marelli inlet air cleaner will bolt to the Magneti Marelli E.F.I. system found on 1995-01 Road Kings and Dressers.