I drilled a 1 3/8' hole in my stock filter and in my airbox. All I noticed was that my right pipe started to turn gold sooner than usual, which tells me that it was too lean. I selected 1 3/8" because I had some chrome button plugs that size. I now have one of those in the bottom of my airbox..... '03 America with 130 mains, no snorkel(s), TBike pipes, and TBS needles.
