I have ran this kit with and without the bd box. I ran twins with a sno pro airbox then i changed it back to the single and stock air box. It ran great either way just didnt like messing with the bd box. Im not sure on the miles I bought it used and only put about 400 on it myself. Just looking at it, it doesnt have many miles. The 15:1 domes are for 10,000ft and up. You can get different domes for different elevations.