The airbox eliminator kits open the air flow up tremendously. The stock airbox and filter are like a giant rag stuffed into the carb intakes. BUT once you open the air up, you should also give it more gas to compensate. (bigger mains and open the exhaust while you're at it)
The drilling of the bottom of the air box will also allow for a big increase in air flow and costs zero and is reversable. The destructions are in the tech vault in the How-To's.
