Tansfer to a lower UAI course = usually internal and little more than paperwork
Transfer to a higher UAI course = external (as in has to be done though UAC rather than whatever uni you're in), a 50/50 weighting of your UAI and your uni marks, I'm pretty sure scaling for uni courses functions somewhat like scaling for HSC subjects so there is no simple formula (though not 100% on that).
Also consider carefully what majors you want because BEc is perfect if:
1. Economics was one of them.
2. You had one major in mind, which an economics major always complements very well.
Also 86 doesen't necessarily get you into BEc, last year was an unusual slump, and is likely to go back up this year.