OBA stands for On Board Air, sorry this is my first post on a non Land Rover forum.
OBA is basically where we take an airconditioning compressor and switch it from its role of keeping you cool to giving you comprssed air on tap.
So if you have A/C and don't want/don't use it ten you can have all the air you need for your air ride system.
Here are a couple of links to land rover forums to show what we did but the pinciple is the same for any engine!
http://forums.lr4x4.com/index.php?showtopic=2115&hl=+board++air
Anyon here doing this yet?
Or will it inspire you to?